Hard braking down hill blowouts

[Ben Kaufman]

Is it normal to have blow-outs on a road bike from prolonged hard braking going
about one mile down a steep hill or should superior wheels and tires be able
to deal with the generated heat? I have an old panasonic but keep the tires and
tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
not the best in the world but a heck of a lot better than what my LBS sold me.
It is a 27 inch rim and I could not find any better quality tires). But is it
the tire/wheel quality at issue? I have been thinking about getting a new bike
rather than trying to upgrade this one for a number of reasons (I don't think
it's even possible to switch to the current wheel size) but the blow-outs are
my biggest justification of expenditure to my wife.

Thanks.

Ben

[jobst.brandt@stanfordalumni.org]

Ben Kaufman wrote:

> Is it normal to have blow-outs on a road bike from prolonged hard
> braking going about one mile down a steep hill or should superior
> wheels and tires be able to deal with the generated heat? I have an
> old Panasonic but keep the tires and tubes up to date
> (Performance Bike GT2 Kevlar, rated at 105 lbs, 26TPI, which are not
> the best in the world but a heck of a lot better than what my LBS
> sold me. It is a 27 inch rim and I could not find any better
> quality tires). But is it the tire/wheel quality at issue? I have
> been thinking about getting a new bike rather than trying to upgrade
> this one for a number of reasons (I don't think it's even possible
> to switch to the current wheel size) but the blow-outs are my
> biggest justification of expenditure to my wife.

This is a traditional problem, so much so that bicycles are prohibited
down certain roads in the Alps. Zirlerberg above Innsbruck is a
classic with six runaway escape ramps for brake failures of trucks.
The Würzen Pass from Slovenia to Austria has a long 18% grade.

Locally in the Santa Clara Valley we have several tire blow-off
descents on Metcalf Road and Hicks and Almaden Roads, each of which
has had fatalities on descents. Tandems are noted for this problem,
especially if the driver isn't careful to use front and rear brakes
equally. For this reason tandems used for mountain touring are best
equipped with hub brakes (drums or disks).

In the days of tubular tires, that were glued onto rims, glue melted
allowing tires to creep and tear off the inflation stem causing rapid
deflation. I experienced that effect in the alps ans later had
clincher blow-offs on the same stretch of the Gotthard Pass.

I instrumented a wheel with pressure sensor and temperature
thermocouple to monitor a blow-off but was unsuccessful getting the
tire to separate even though temperature reached 150 degC and pressure
125 psi. The mechanism for blow-off is still unclear but it seams the
bead material softens and creeps of the hooked bead of the rim.

On steep descents after riding through water, I have generated steam
that came hissing out of the rim from around the stem as I braked for
successive hairpin turns on the Nufenen Pass in the Alps.

Jobst Brandt

[Ben C]

On 2008-03-28, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-dollars@pobox.com> wrote:
> Is it normal to have blow-outs on a road bike from prolonged hard
> braking going about one mile down a steep hill or should superior
> wheels and tires be able to deal with the generated heat? I have an
> old panasonic but keep the tires and tubes up to date (PerfomanceBike
> GT2 Kevlar, rated at 105 lbs, 26TPI, which are not the best in the
> world but a heck of a lot better than what my LBS sold me. It is a
> 27 inch rim and I could not find any better quality tires). But is it
> the tire/wheel quality at issue? I have been thinking about getting a
> new bike rather than trying to upgrade this one for a number of
> reasons (I don't think it's even possible to switch to the current
> wheel size) but the blow-outs are my biggest justification of
> expenditure to my wife.

Some math I did earlier:

http://groups.google.co.uk/group/uk.rec.cycling/msg/991d32532f671264

It's probably all wrong off course, but my tentative conclusion from it
is that the rims act as heat sinks-- they can soak up quite a lot of
energy, enough for most purposes, but they can't really cope with
sustained braking.

Disks on the other hand have much less heat capacity (because they're
smaller) and probably work hotter, so I reckon they might get up to
temperature quite quickly and then dissipate more because of the bigger
temperature difference with the surrounding air. This would mean they
should be better for continuous braking. In any case they won't make the
tyres pop off.

[Hobbes@spnb&s.com]

On Thu, 27 Mar 2008 22:06:48 -0400, Ben Kaufman
<spaXm-mXe-anXd-paXy-5000-dollars@pobox.com> wrote:

>Is it normal to have blow-outs on a road bike from prolonged hard braking going
>about one mile down a steep hill or should superior wheels and tires be able
>to deal with the generated heat? I have an old panasonic but keep the tires and
>tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
>not the best in the world but a heck of a lot better than what my LBS sold me.
>It is a 27 inch rim and I could not find any better quality tires). But is it
>the tire/wheel quality at issue? I have been thinking about getting a new bike
>rather than trying to upgrade this one for a number of reasons (I don't think
>it's even possible to switch to the current wheel size) but the blow-outs are
>my biggest justification of expenditure to my wife.

Actual blow outs or is the tire moving on the rim and tearing the stem?

Just asking because the latter is more common but the former more often blamed.

[SMS]

Ben Kaufman wrote:
> Is it normal to have blow-outs on a road bike from prolonged hard braking going
> about one mile down a steep hill or should superior wheels and tires be able
> to deal with the generated heat?

It's normal. Pump your brakes rather than having them on all the time,
and stop occasionally to let them cool. That said, it does vary with rim
and tires. It's not the air in the tube expanding because of the heat
that causes the blow out, it's the rim getting too hot.

Are your rims straight side or hook edge? What kind of bead does the GT2
tire have (steel or kevlar)? Sheldon's shop sells some 27" steel bead
tires. See "http://www.sheldonbrown.com/harris/tires/630.html"

Also, for a good and amusing tutorial by Sheldon about folding steel
bead tires, see "http://www.sheldonbrown.com/video/tire-folding.html".
Remember, red is the only color that works, LOL.

On tandems, there was (or is) often a drum brake to use as a drag break
when descending steep hills. A disc brake doesn't work well as a drag
brake, as the rotor will warp and the pad will quickly be worn down.

I have an old panasonic but keep the tires and
> tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
> not the best in the world but a heck of a lot better than what my LBS sold me.
> It is a 27 inch rim and I could not find any better quality tires). But is it
> the tire/wheel quality at issue? I have been thinking about getting a new bike
> rather than trying to upgrade this one for a number of reasons (I don't think
> it's even possible to switch to the current wheel size) but the blow-outs are
> my biggest justification of expenditure to my wife.

It's a good justification. Get a road bike with disc brakes. It will
eliminate the blow outs, but if you ride with the brakes constantly on
you'll go through a lot of pads and rotors.

[datakoll]

On Mar 27, 10:06*pm, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-
doll...@pobox.com> wrote:
> Is it normal to have blow-outs on a road bike from prolonged hard braking going
> about one mile down *a *steep hill *or should superior wheels and tires be able
> to deal with the generated heat? *I have an old panasonic but keep the tires and
> tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, *which are
> not the best in the world but *a heck of a lot better than what my LBS sold me.
> It is a *27 inch rim and I could not find any better quality tires). *But is it
> the tire/wheel quality at issue? *I have been thinking about getting a new bike
> rather than trying to *upgrade this one for a number of reasons (I don't think
> it's even possible to switch to the current wheel size) but *the blow-outs are
> my biggest justification of expenditure to my wife.
>
> Thanks.
>
> Ben

How many times do you bake from X to Y ? and how long are the times
from braking point A to BP B?

I wrote the following last night. Sidewall dirt at the bead is
relatively invisible under normal shop conditions.
a thorough all surfaces cleaning before reassembly helps (and before
disassembly) then pull and push nipple in and out to seat and pinch
pinch pinch sidewalls inward thoroughly all around before and then
maybe during the first pounds going in.
once in a while when placing a new tube in, I'll soap, soak and brush
sidewalls clean. I cover the sidewalls with FL teflon wax on the bead
then overspray the area with belt conditioner as brake prep so the
dirt is on that surface, floats away when soaping. after it gets
beaten with a stick.

[datakoll]

On Mar 27, 10:06*pm, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-
doll...@pobox.com> wrote:
> Is it normal to have blow-outs on a road bike from prolonged hard braking going
> about one mile down *a *steep hill *or should superior wheels and tires be able
> to deal with the generated heat? *I have an old panasonic but keep the tires and
> tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, *which are
> not the best in the world but *a heck of a lot better than what my LBS sold me.
> It is a *27 inch rim and I could not find any better quality tires). *But is it
> the tire/wheel quality at issue? *I have been thinking about getting a new bike
> rather than trying to *upgrade this one for a number of reasons (I don't think
> it's even possible to switch to the current wheel size) but *the blow-outs are
> my biggest justification of expenditure to my wife.
>
> Thanks.
>
> Ben

btw. BEN, do you know what reconditioned Panasonics are fetching on
Ebay?

[Ron George]

On Mar 27, 10:06 pm, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-
doll...@pobox.com> wrote:
> Is it normal to have blow-outs on a road bike from prolonged hard braking going
> about one mile down a steep hill or should superior wheels and tires be able
> to deal with the generated heat? I have an old panasonic but keep the tires and
> tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
> not the best in the world but a heck of a lot better than what my LBS sold me.
> It is a 27 inch rim and I could not find any better quality tires). But is it
> the tire/wheel quality at issue? I have been thinking about getting a new bike
> rather than trying to upgrade this one for a number of reasons (I don't think
> it's even possible to switch to the current wheel size) but the blow-outs are
> my biggest justification of expenditure to my wife.
>
> Thanks.
>
> Ben

Ben,

Here are some tubulars popping off wheels. Famous accidents of the
Tour de France. http://cozybeehive.blogspot.com/2007/11/tubulars-exploding-and-peeling-off.html

This is an interesting discussion, I'm watching where its leading.

Ron
http://cozybeehive.blogspot.com

[jobst.brandt@stanfordalumni.org]

Zirlerberg:

http://www.sagen.at/texte/gegenwart/oesterreich/tirol/allgemein/picknickamzirlerberg.htm

Jobst Brandt

[sergio]

On 28 Mar, 06:35, jobst.bra...@stanfordalumni.org wrote:

> In the days of tubular tires, that were glued onto rims, glue melted
> allowing tires to creep and tear off the inflation stem causing rapid
> deflation. *I experienced that effect in the alps ans later had
> clincher blow-offs on the same stretch of the Gotthard Pass.

Not to dispute or anything, but where was that?
Down the south side of the old Tremola, perhaps?

Sergio
Pisa

[dustoyevsky@mac.com]

On Mar 28, 12:35*am, jobst.bra...@stanfordalumni.org wrote:

> I instrumented a wheel with pressure sensor and temperature
> thermocouple to monitor a blow-off but was unsuccessful getting the
> tire to separate even though temperature reached 150 degC and pressure
> 125 psi. *The mechanism for blow-off is still unclear but it seams the
> bead material softens and creeps of the hooked bead of the rim.

Some people, more successful than you (by report) (ha ha) (sorry, that
one kinda just popped out) in getting tires to blow off, use the
advantage of starting with much higher pressures. "I run 140". Yo!
Obeying the advertising...

At some point, I saw HED warning against use of a certain tire brand.
Seemed to imply that prolonged braking might not be entirely necessary
to provoke a blowoff.

Since I had some of each in the fleet, I looked at a Specialized/HED
Trispoke rim and a (IMS) Brand C tire. I noticed the bead was much too
large to fit all the way, so to speak, into the hooked bead area in
the rim.

"Already on the way out?" when inflated-- or was that over-inflated? A
nice, rounded slope on the tire bead, not much to hook into there.

Other tires, with much smaller beads, seemed to fit nicely, with the
rim perhaps (no x-ray machine on the premises) finding purchase where
the bead stops and the sidewall begins, as would seem to be the intent
of the design. --D-y

[Larry Dickman]

jobst.brandt@stanfordalumni.org wrote in news:47ec8385$0$36349
$742ec2ed@news.sonic.net:

> I instrumented a wheel with pressure sensor and temperature
> thermocouple to monitor a blow-off but was unsuccessful getting the
> tire to separate even though temperature reached 150 degC and pressure
> 125 psi. The mechanism for blow-off is still unclear but it seams the
> bead material softens and creeps of the hooked bead of the rim.
>
> On steep descents after riding through water, I have generated steam
> that came hissing out of the rim from around the stem as I braked for
> successive hairpin turns on the Nufenen Pass in the Alps.

A good reason to not use plastic rim strips. I've had these red plastic rim
strips extrude into the spoke holes causing the tube to rupture.

--
Larry Dickman <LDickman@comcast.net>

[Ben Kaufman]

On 28 Mar 2008 05:35:01 GMT, jobst.brandt@stanfordalumni.org wrote:

>Ben Kaufman wrote:
>
>> Is it normal to have blow-outs on a road bike from prolonged hard
>> braking going about one mile down a steep hill or should superior
>> wheels and tires be able to deal with the generated heat? I have an
>> old Panasonic but keep the tires and tubes up to date
>> (Performance Bike GT2 Kevlar, rated at 105 lbs, 26TPI, which are not
>> the best in the world but a heck of a lot better than what my LBS
>> sold me. It is a 27 inch rim and I could not find any better
>> quality tires). But is it the tire/wheel quality at issue? I have
>> been thinking about getting a new bike rather than trying to upgrade
>> this one for a number of reasons (I don't think it's even possible
>> to switch to the current wheel size) but the blow-outs are my
>> biggest justification of expenditure to my wife.
>
>This is a traditional problem, so much so that bicycles are prohibited
>down certain roads in the Alps. Zirlerberg above Innsbruck is a
>classic with six runaway escape ramps for brake failures of trucks.
>The Würzen Pass from Slovenia to Austria has a long 18% grade.
>
>Locally in the Santa Clara Valley we have several tire blow-off
>descents on Metcalf Road and Hicks and Almaden Roads, each of which
>has had fatalities on descents. Tandems are noted for this problem,
>especially if the driver isn't careful to use front and rear brakes
>equally. For this reason tandems used for mountain touring are best
>equipped with hub brakes (drums or disks).
>
>In the days of tubular tires, that were glued onto rims, glue melted
>allowing tires to creep and tear off the inflation stem causing rapid
>deflation. I experienced that effect in the alps ans later had
>clincher blow-offs on the same stretch of the Gotthard Pass.
>
>I instrumented a wheel with pressure sensor and temperature
>thermocouple to monitor a blow-off but was unsuccessful getting the
>tire to separate even though temperature reached 150 degC and pressure
>125 psi. The mechanism for blow-off is still unclear but it seams the
>bead material softens and creeps of the hooked bead of the rim.
>
>On steep descents after riding through water, I have generated steam
>that came hissing out of the rim from around the stem as I braked for
>successive hairpin turns on the Nufenen Pass in the Alps.
>
>Jobst Brandt

Darn, I may just have to avoid this hill in warmer weather :-)

Ben

[Bill Bushnell]

jobst.brandt@stanfordalumni.org wrote:
> I instrumented a wheel with pressure sensor and temperature
> thermocouple to monitor a blow-off but was unsuccessful getting the
> tire to separate even though temperature reached 150 degC and pressure
> 125 psi. The mechanism for blow-off is still unclear but it seams the
> bead material softens and creeps of the hooked bead of the rim.

I stopped getting blowoffs when I reduced cold inflation pressure from 85 to 75
psi (Ritchey Tom Slick, 559x36 on Ritchey rim). I believe that the likelihood of
blowoff may be especially sensitive to inflation pressure because even though
I've been riding around lately with an extra 45 lbs. on the bike, I still don't
get blowoffs, even on the roads where they are likely to occur (Hicks, Vista
Verde/Ramona, etc.)

Perhaps you would consider repeating your test with incrementally more air
pressure in your tire.

--
Bill Bushnell
http://pobox.com/~bushnell/

[jobst.brandt@stanfordalumni.org]

Sergio Servadio wrote:

>> In the days of tubular tires, that were glued onto rims, glue
>> melted allowing tires to creep and tear off the inflation stem
>> causing rapid deflation. Â*I experienced that effect in the alps ans
>> later had clincher blow-offs on the same stretch of the Gotthard
>> Pass.

> Not to dispute or anything, but where was that? Down the south side
> of the old Tremola, perhaps?

Yes, on the last hairpin turn leading to the Fortezza.

Jobst Brandt

[sergio]

On Mar 28, 9:49 am, Ben C <spams...@spam.eggs> wrote:

> Disks on the other hand have much less heat capacity

Nor do they exchannge heat with the tyre.

Sergio
Pisa

[Marz]

On Mar 28, 3:49 am, Ben C <spams...@spam.eggs> wrote:
> On 2008-03-28, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-doll...@pobox.com> wrote:
>
> > Is it normal to have blow-outs on a road bike from prolonged hard
> > braking going about one mile down a steep hill or should superior
> > wheels and tires be able to deal with the generated heat? I have an
> > old panasonic but keep the tires and tubes up to date (PerfomanceBike
> > GT2 Kevlar, rated at 105 lbs, 26TPI, which are not the best in the
> > world but a heck of a lot better than what my LBS sold me. It is a
> > 27 inch rim and I could not find any better quality tires). But is it
> > the tire/wheel quality at issue? I have been thinking about getting a
> > new bike rather than trying to upgrade this one for a number of
> > reasons (I don't think it's even possible to switch to the current
> > wheel size) but the blow-outs are my biggest justification of
> > expenditure to my wife.
>
> Some math I did earlier:
>
> http://groups.google.co.uk/group/uk.rec.cycling/msg/991d32532f671264
>
> It's probably all wrong off course, but my tentative conclusion from it
> is that the rims act as heat sinks-- they can soak up quite a lot of
> energy, enough for most purposes, but they can't really cope with
> sustained braking.
>
> Disks on the other hand have much less heat capacity (because they're
> smaller) and probably work hotter, so I reckon they might get up to
> temperature quite quickly and then dissipate more because of the bigger
> temperature difference with the surrounding air. This would mean they
> should be better for continuous braking. In any case they won't make the
> tyres pop off.

Disk brakes have their own problems with heat and can 'fade' (fail) on
long downhill sections.

From hayes...

"Brake Fluid Fade - This type of fade occurs when the brake fluid
inside a hydraulic caliper boils. An important characteristic of
brake fluid is that it is incompressible. When a brake fluid boils,
gas is formed within the system that is compressible and any lever
stroke available goes toward compressing the gas instead of generating
brake power. Interestingly enough, when a fluid is under pressure, it
is very difficult for the fluid to boil. If a brake system is under
pressure, the fluid temperature can rise above the boiling temperature
without the fluid actually boiling. Once the pressure is released,
the fluid will instantly boil and fade will occur."

A common practice for long downhill sections when using disk brakes is
to brake hard and release as opposed to constant braking to control
speed. The idea being, that when you release you allow the disk to
cool slighty.

I've experienced disk brake fade more often than rim brake blow outs
and that the disk brake fade occurs quicker during a descent than a
rim brake blow out. But, the offroad trails I ride are on average alot
steeper than the roads I ride and also require alot more braking.

Laters,

Marz

[Ben C]

On 2008-03-28, sergio <servadio@df.unipi.it> wrote:
> On Mar 28, 9:49 am, Ben C <spams...@spam.eggs> wrote:
>
>> Disks on the other hand have much less heat capacity
>
> Nor do they exchannge heat with the tyre.

Indeed. I wonder if they ever melt the grease in the hub though.

[jobst.brandt@stanfordalumni.org]

Ben C? wrote:

>>> Disks on the other hand have much less heat capacity

>> Nor do they exchange heat with the tyre.

> Indeed. I wonder if they ever melt the grease in the hub though.

Most bicycle disks are mounted on support spiders so flimsy that heat
conduction to the bearings is insignificant.

Jobst Brandt

[jim beam]

jobst.brandt@stanfordalumni.org wrote:
> Ben C? wrote:
>
>>>> Disks on the other hand have much less heat capacity
>
>>> Nor do they exchange heat with the tyre.
>
>> Indeed. I wonder if they ever melt the grease in the hub though.
>
> Most bicycle disks are mounted on support spiders so flimsy that heat
> conduction to the bearings is insignificant.
>

"flimsy"??? is that stanford parlance for "stainless [disk] steel is a
poor conductor"? or is it presumptive nonsense from someone that
doesn't know what they're talking about?

[Marz]

On Mar 28, 9:03*am, jim beam <spamvor...@bad.example.net> wrote:
> jobst.bra...@stanfordalumni.org wrote:
> > Ben C? wrote:
>
> >>>> Disks on the other hand have much less heat capacity
>
> >>> Nor do they exchange heat with the tyre.
>
> >> Indeed. *I wonder if they ever melt the grease in the hub though.
>
> > Most bicycle disks are mounted on support spiders so flimsy that heat
> > conduction to the bearings is insignificant.
>
> "flimsy"??? *is that stanford parlance for "stainless [disk] steel is a
> poor conductor"? *or is it presumptive nonsense from someone that
> doesn't know what they're talking about?

Disks are very flimsy and are not constructed to resist side to side
forces. They're only 'stiff' in the direction of the rotating wheel.
And not all disks are contructed with stainless steel spiders (see
Hope).

For example you could poor water on a hot rim to cool it, but the same
action on a disk may (and has for me) warp the bloody thing.

laters,

Marz

[Jay Beattie]

On Mar 28, 8:26*am, Marz <marzjenni...@gmail.com> wrote:
> On Mar 28, 3:49 am, Ben C <spams...@spam.eggs> wrote:
>
>
>
>
>
> > On 2008-03-28, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-doll...@pobox.com> wrote:
>
> > > Is it normal to have blow-outs on a road bike from prolonged hard
> > > braking going about one mile down *a *steep hill *or should superior
> > > wheels and tires be able to deal with the generated heat? *I have an
> > > old panasonic but keep the tires and tubes up to date (PerfomanceBike
> > > GT2 Kevlar, rated at 105 lbs, 26TPI, *which are not the best in the
> > > world but *a heck of a lot better than what my LBS sold me. It is a
> > > 27 inch rim and I could not find any better quality tires). *But is it
> > > the tire/wheel quality at issue? *I have been thinking about getting a
> > > new bike rather than trying to *upgrade this one for a number of
> > > reasons (I don't think it's even possible to switch to the current
> > > wheel size) but *the blow-outs are my biggest justification of
> > > expenditure to my wife.
>
> > Some math I did earlier:
>
> >http://groups.google.co.uk/group/uk.rec.cycling/msg/991d32532f671264
>
> > It's probably all wrong off course, but my tentative conclusion from it
> > is that the rims act as heat sinks-- they can soak up quite a lot of
> > energy, enough for most purposes, but they can't really cope with
> > sustained braking.
>
> > Disks on the other hand have much less heat capacity (because they're
> > smaller) and probably work hotter, so I reckon they might get up to
> > temperature quite quickly and then dissipate more because of the bigger
> > temperature difference with the surrounding air. This would mean they
> > should be better for continuous braking. In any case they won't make the
> > tyres pop off.
>
> Disk brakes have their own problems with heat and can 'fade' (fail) on
> long downhill sections.
>
> From hayes...
>
> "Brake Fluid Fade - This type of fade occurs when the brake fluid
> inside a hydraulic caliper boils. *An important characteristic of
> brake fluid is that it is incompressible. *When a brake fluid boils,
> gas is formed within the system that is compressible and any lever
> stroke available goes toward compressing the gas instead of generating
> brake power. *Interestingly enough, when a fluid is under pressure, it
> is very difficult for the fluid to boil. *If a brake system is under
> pressure, the fluid temperature can rise above the boiling temperature
> without the fluid actually boiling. *Once the pressure is released,
> the fluid will instantly boil and fade will occur."
>
> A common practice for long downhill sections when using disk brakes is
> to brake hard and release as opposed to constant braking to control
> speed. The idea being, that when you release you allow the disk to
> cool slighty.
>
> I've experienced disk brake fade more often than rim brake blow outs
> and that the disk brake fade occurs quicker during a descent than a
> rim brake blow out. But, the offroad trails I ride are on average alot
> steeper than the roads I ride and also require alot more braking.

I think that is an important point -- road versus trail. I have done
long road descents on my mechanical disk equiped cross bike without
any brake fade. In fact, in the rain, the disks are far better than
my rim brakes. There is a local 14 mile descent that I did in the
rain/snow on my cross bike with good stopping all the way to the
bottom -- which was a good thing because my hands were frozen, and I
couldn't generate much force on my levers. -- Jay Beattie.

[Ben C]

On 2008-03-28, Marz <marzjennings@gmail.com> wrote:
> On Mar 28, 3:49 am, Ben C <spams...@spam.eggs> wrote:
>> On 2008-03-28, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-doll...@pobox.com> wrote:
[...]
> Disk brakes have their own problems with heat and can 'fade' (fail) on
> long downhill sections.
>
> From hayes...
>
> "Brake Fluid Fade - This type of fade occurs when the brake fluid
> inside a hydraulic caliper boils. An important characteristic of
> brake fluid is that it is incompressible. When a brake fluid boils,
> gas is formed within the system that is compressible and any lever
> stroke available goes toward compressing the gas instead of generating
> brake power. Interestingly enough, when a fluid is under pressure, it
> is very difficult for the fluid to boil. If a brake system is under
> pressure, the fluid temperature can rise above the boiling temperature
> without the fluid actually boiling. Once the pressure is released,
> the fluid will instantly boil and fade will occur."
>
> A common practice for long downhill sections when using disk brakes is
> to brake hard and release as opposed to constant braking to control
> speed. The idea being, that when you release you allow the disk to
> cool slighty.
>
> I've experienced disk brake fade more often than rim brake blow outs
> and that the disk brake fade occurs quicker during a descent than a
> rim brake blow out. But, the offroad trails I ride are on average alot
> steeper than the roads I ride and also require alot more braking.

I have heard of fluid fade affecting bicycle brakes before. It is
shocking in my opinion because that's the easiest kind of fade to fix--
you just need brake fluid that doesn't boil, which exists. There's no
tradeoff or anything, it's a win-win no-brainer. Cars haven't suffered
from fluid fade for years with modern decent brake fluid.

I mentioned this before and someone said it's because bicycle brakes use
crappy brake fluid because it doesn't strip the paint. My advice: use
proper car brake fluid in your bike brakes but pour it in carefully and
don't spill it.

[Michael Press]

In article
<04d83991-8e34-4954-9882-dd742be9b56a@f63g2000hsf.googlegroups.com>,
Marz <marzjennings@gmail.com> wrote:

> A common practice for long downhill sections when using disk brakes is
> to brake hard and release as opposed to constant braking to control
> speed. The idea being, that when you release you allow the disk to
> cool slighty.

Yes. The idea is to heat the disc quickly and very
hot. The convective cooling to the air is faster at
higher temperature. The heat transfer to the hub and
brake assemblies is reduced because the disc can cool
to a lower temperature before it is heated again, and
the brake assembly can also cool.

--
Michael Press

[jim beam]

Marz wrote:
> On Mar 28, 9:03�am, jim beam <spamvor...@bad.example.net> wrote:
>> jobst.bra...@stanfordalumni.org wrote:
>>> Ben C? wrote:
>>>>>> Disks on the other hand have much less heat capacity
>>>>> Nor do they exchange heat with the tyre.
>>>> Indeed. �I wonder if they ever melt the grease in the hub though.
>>> Most bicycle disks are mounted on support spiders so flimsy that heat
>>> conduction to the bearings is insignificant.
>> "flimsy"??? �is that stanford parlance for "stainless [disk] steel is a
>> poor conductor"? �or is it presumptive nonsense from someone that
>> doesn't know what they're talking about?
>
> Disks are very flimsy and are not constructed to resist side to side
> forces. They're only 'stiff' in the direction of the rotating wheel.
> And not all disks are contructed with stainless steel spiders (see
> Hope).

stiffness has absolutely nothing to do with thermal conductivity. or
surface thermal transfer to air.


>
> For example you could poor water on a hot rim to cool it, but the same
> action on a disk may (and has for me) warp the bloody thing.
>
> laters,
>
> Marz

[Hank]

On Mar 28, 9:30 am, Jay Beattie <jbeat...@lindsayhart.com> wrote:
> On Mar 28, 8:26 am, Marz <marzjenni...@gmail.com> wrote:
>
>
>
> > On Mar 28, 3:49 am, Ben C <spams...@spam.eggs> wrote:
>
> > > On 2008-03-28, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-doll...@pobox.com> wrote:
>
> > > > Is it normal to have blow-outs on a road bike from prolonged hard
> > > > braking going about one mile down a steep hill or should superior
> > > > wheels and tires be able to deal with the generated heat? I have an
> > > > old panasonic but keep the tires and tubes up to date (PerfomanceBike
> > > > GT2 Kevlar, rated at 105 lbs, 26TPI, which are not the best in the
> > > > world but a heck of a lot better than what my LBS sold me. It is a
> > > > 27 inch rim and I could not find any better quality tires). But is it
> > > > the tire/wheel quality at issue? I have been thinking about getting a
> > > > new bike rather than trying to upgrade this one for a number of
> > > > reasons (I don't think it's even possible to switch to the current
> > > > wheel size) but the blow-outs are my biggest justification of
> > > > expenditure to my wife.
>
> > > Some math I did earlier:
>
> > >http://groups.google.co.uk/group/uk.rec.cycling/msg/991d32532f671264
>
> > > It's probably all wrong off course, but my tentative conclusion from it
> > > is that the rims act as heat sinks-- they can soak up quite a lot of
> > > energy, enough for most purposes, but they can't really cope with
> > > sustained braking.
>
> > > Disks on the other hand have much less heat capacity (because they're
> > > smaller) and probably work hotter, so I reckon they might get up to
> > > temperature quite quickly and then dissipate more because of the bigger
> > > temperature difference with the surrounding air. This would mean they
> > > should be better for continuous braking. In any case they won't make the
> > > tyres pop off.
>
> > Disk brakes have their own problems with heat and can 'fade' (fail) on
> > long downhill sections.
>
> > From hayes...
>
> > "Brake Fluid Fade - This type of fade occurs when the brake fluid
> > inside a hydraulic caliper boils. An important characteristic of
> > brake fluid is that it is incompressible. When a brake fluid boils,
> > gas is formed within the system that is compressible and any lever
> > stroke available goes toward compressing the gas instead of generating
> > brake power. Interestingly enough, when a fluid is under pressure, it
> > is very difficult for the fluid to boil. If a brake system is under
> > pressure, the fluid temperature can rise above the boiling temperature
> > without the fluid actually boiling. Once the pressure is released,
> > the fluid will instantly boil and fade will occur."
>
> > A common practice for long downhill sections when using disk brakes is
> > to brake hard and release as opposed to constant braking to control
> > speed. The idea being, that when you release you allow the disk to
> > cool slighty.
>
> > I've experienced disk brake fade more often than rim brake blow outs
> > and that the disk brake fade occurs quicker during a descent than a
> > rim brake blow out. But, the offroad trails I ride are on average alot
> > steeper than the roads I ride and also require alot more braking.
>
> I think that is an important point -- road versus trail. I have done
> long road descents on my mechanical disk equiped cross bike without
> any brake fade.

Well, yeah - if it's mechanical, the fluid definitely won't boil!

[SMS]

Jay Beattie wrote:
> On Mar 28, 8:26 am, Marz <marzjenni...@gmail.com> wrote:

>> I've experienced disk brake fade more often than rim brake blow outs
>> and that the disk brake fade occurs quicker during a descent than a
>> rim brake blow out. But, the offroad trails I ride are on average alot
>> steeper than the roads I ride and also require alot more braking.
>
> I think that is an important point -- road versus trail. I have done
> long road descents on my mechanical disk equiped cross bike without
> any brake fade. In fact, in the rain, the disks are far better than
> my rim brakes. There is a local 14 mile descent that I did in the
> rain/snow on my cross bike with good stopping all the way to the
> bottom -- which was a good thing because my hands were frozen, and I
> couldn't generate much force on my levers. -- Jay Beattie.

Yeah, the problem with disk brake fade is more common with hydraulic
disk brakes than mechanical disk brakes. Always use non-hydraulic disk
brakes if retro-fitting, and look for mechanical disk brakes on new
bicycles as well.

[sergio]

On Mar 28, 5:29 pm, Hobbes@spnb&s.com wrote:

> Actual blow outs or is the tire moving on the rim and tearing the stem?

It certainly depends on whether one has clinchers or tubular tyres.

Sergio
Pisa

[Ben Kaufman]

On Fri, 28 Mar 2008 12:29:10 -0400, Hobbes@spnb&s.com wrote:

>On Thu, 27 Mar 2008 22:06:48 -0400, Ben Kaufman
><spaXm-mXe-anXd-paXy-5000-dollars@pobox.com> wrote:
>
>>Is it normal to have blow-outs on a road bike from prolonged hard braking going
>>about one mile down a steep hill or should superior wheels and tires be able
>>to deal with the generated heat? I have an old panasonic but keep the tires and
>>tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
>>not the best in the world but a heck of a lot better than what my LBS sold me.
>>It is a 27 inch rim and I could not find any better quality tires). But is it
>>the tire/wheel quality at issue? I have been thinking about getting a new bike
>>rather than trying to upgrade this one for a number of reasons (I don't think
>>it's even possible to switch to the current wheel size) but the blow-outs are
>>my biggest justification of expenditure to my wife.
>
>Actual blow outs or is the tire moving on the rim and tearing the stem?
>
>Just asking because the latter is more common but the former more often blamed.

No, the tire stayed on the rim. I heard the bang but at first could not tell
which tire had blown - fortunately, I was going under 10mph at the time. The
location of the failure on the tube was about 1/3 of the way around from the
stem and was a 2 inch appearing "slit." In other blowouts I have felt a tell
tale "thump thump" before it blew, and usually in those the tire is taken off
the rim, which makes the tube replacement process that much faster :-)

Ben

[Larry Dickman]

Ben C <spamspam@spam.eggs> wrote in
news:slrnfuqb03.1fs.spamspam@bowser.marioworld:

> I have heard of fluid fade affecting bicycle brakes before. It is
> shocking in my opinion because that's the easiest kind of fade to
> fix-- you just need brake fluid that doesn't boil, which exists.
> There's no tradeoff or anything, it's a win-win no-brainer. Cars
> haven't suffered from fluid fade for years with modern decent brake
> fluid.
>
> I mentioned this before and someone said it's because bicycle brakes
> use crappy brake fluid because it doesn't strip the paint. My advice:
> use proper car brake fluid in your bike brakes but pour it in
> carefully and don't spill it.

Many (probably most) hydraulic disc brakes for bikes use DOT 3 or 4 brake
fluids. The problem still exists, especially if there is water in the
system. Also, one should never put DOT fluid in a system designed for
mineral oil and vice versa. The seals may not be compatible. All this said,
I've never had any problems on my mountain bike equipped with hydraulic
brakes.

--
Larry Dickman <LDickman@comcast.net>

[jim beam]

Ben C wrote:
> On 2008-03-28, Marz <marzjennings@gmail.com> wrote:
>> On Mar 28, 3:49 am, Ben C <spams...@spam.eggs> wrote:
>>> On 2008-03-28, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-doll...@pobox.com> wrote:
> [...]
>> Disk brakes have their own problems with heat and can 'fade' (fail) on
>> long downhill sections.
>>
>> From hayes...
>>
>> "Brake Fluid Fade - This type of fade occurs when the brake fluid
>> inside a hydraulic caliper boils. An important characteristic of
>> brake fluid is that it is incompressible. When a brake fluid boils,
>> gas is formed within the system that is compressible and any lever
>> stroke available goes toward compressing the gas instead of generating
>> brake power. Interestingly enough, when a fluid is under pressure, it
>> is very difficult for the fluid to boil. If a brake system is under
>> pressure, the fluid temperature can rise above the boiling temperature
>> without the fluid actually boiling. Once the pressure is released,
>> the fluid will instantly boil and fade will occur."
>>
>> A common practice for long downhill sections when using disk brakes is
>> to brake hard and release as opposed to constant braking to control
>> speed. The idea being, that when you release you allow the disk to
>> cool slighty.
>>
>> I've experienced disk brake fade more often than rim brake blow outs
>> and that the disk brake fade occurs quicker during a descent than a
>> rim brake blow out. But, the offroad trails I ride are on average alot
>> steeper than the roads I ride and also require alot more braking.
>
> I have heard of fluid fade affecting bicycle brakes before. It is
> shocking in my opinion because that's the easiest kind of fade to fix--
> you just need brake fluid that doesn't boil, which exists. There's no
> tradeoff or anything, it's a win-win no-brainer. Cars haven't suffered
> from fluid fade for years with modern decent brake fluid.
>
> I mentioned this before and someone said it's because bicycle brakes use
> crappy brake fluid because it doesn't strip the paint. My advice: use
> proper car brake fluid in your bike brakes but pour it in carefully and
> don't spill it.

or if you do, wash it off immediately with water. wash, never wipe.

[Jay Beattie]

On Mar 28, 11:59*am, Hank <h...@wirtznet.net> wrote:
> On Mar 28, 9:30 am, Jay Beattie <jbeat...@lindsayhart.com> wrote:
>
>
>
>
>
> > On Mar 28, 8:26 am, Marz <marzjenni...@gmail.com> wrote:
>
> > > On Mar 28, 3:49 am, Ben C <spams...@spam.eggs> wrote:
>
> > > > On 2008-03-28, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-doll...@pobox.com> wrote:
>
> > > > > Is it normal to have blow-outs on a road bike from prolonged hard
> > > > > braking going about one mile down *a *steep hill *or should superior
> > > > > wheels and tires be able to deal with the generated heat? *I have an
> > > > > old panasonic but keep the tires and tubes up to date (PerfomanceBike
> > > > > GT2 Kevlar, rated at 105 lbs, 26TPI, *which are not the best in the
> > > > > world but *a heck of a lot better than what my LBS sold me. It is a
> > > > > 27 inch rim and I could not find any better quality tires). *But is it
> > > > > the tire/wheel quality at issue? *I have been thinking about getting a
> > > > > new bike rather than trying to *upgrade this one for a number of
> > > > > reasons (I don't think it's even possible to switch to the current
> > > > > wheel size) but *the blow-outs are my biggest justification of
> > > > > expenditure to my wife.
>
> > > > Some math I did earlier:
>
> > > >http://groups.google.co.uk/group/uk.rec.cycling/msg/991d32532f671264
>
> > > > It's probably all wrong off course, but my tentative conclusion from it
> > > > is that the rims act as heat sinks-- they can soak up quite a lot of
> > > > energy, enough for most purposes, but they can't really cope with
> > > > sustained braking.
>
> > > > Disks on the other hand have much less heat capacity (because they're
> > > > smaller) and probably work hotter, so I reckon they might get up to
> > > > temperature quite quickly and then dissipate more because of the bigger
> > > > temperature difference with the surrounding air. This would mean they
> > > > should be better for continuous braking. In any case they won't make the
> > > > tyres pop off.
>
> > > Disk brakes have their own problems with heat and can 'fade' (fail) on
> > > long downhill sections.
>
> > > From hayes...
>
> > > "Brake Fluid Fade - This type of fade occurs when the brake fluid
> > > inside a hydraulic caliper boils. *An important characteristic of
> > > brake fluid is that it is incompressible. *When a brake fluid boils,
> > > gas is formed within the system that is compressible and any lever
> > > stroke available goes toward compressing the gas instead of generating
> > > brake power. *Interestingly enough, when a fluid is under pressure, it
> > > is very difficult for the fluid to boil. *If a brake system is under
> > > pressure, the fluid temperature can rise above the boiling temperature
> > > without the fluid actually boiling. *Once the pressure is released,
> > > the fluid will instantly boil and fade will occur."
>
> > > A common practice for long downhill sections when using disk brakes is
> > > to brake hard and release as opposed to constant braking to control
> > > speed. The idea being, that when you release you allow the disk to
> > > cool slighty.
>
> > > I've experienced disk brake fade more often than rim brake blow outs
> > > and that the disk brake fade occurs quicker during a descent than a
> > > rim brake blow out. But, the offroad trails I ride are on average alot
> > > steeper than the roads I ride and also require alot more braking.
>
> > I think that is an important point -- road versus trail. *I have done
> > long road descents on my mechanical disk equiped cross bike without
> > any brake fade.
>
> Well, yeah - if it's mechanical, the fluid definitely won't boil!- Hide quoted text -

My cables boil! I was thinking of friction material fade. I totally
glossed over the brake fluid boiling issue. It would seem to me that
you could divert brake fluid heat in to a radiant loop to power a
steam generator for the ride up the other side of the hill. Carl can
probably find a filed patent for that. -- Jay Beattie.

[carlfogel@comcast.net]

On Fri, 28 Mar 2008 12:15:25 -0700 (PDT), Jay Beattie
<jbeattie@lindsayhart.com> wrote:

>My cables boil! I was thinking of friction material fade. I totally
>glossed over the brake fluid boiling issue. It would seem to me that
>you could divert brake fluid heat in to a radiant loop to power a
>steam generator for the ride up the other side of the hill. Carl can
>probably find a filed patent for that. -- Jay Beattie.

Dear Jay,

Alas, re-generative braking systems are notoriously inefficient, so
early inventors concentrated on worthier steam-powered bicycles:

http://www.dself.dsl.pipex.com/MUSEUM/TRANSPORT/steambike/steambike.htm

The Michaux steam velocipede is the epitome of elegance and good
looks, but the Roper was far more efficient.

Details on the Roper, whose inventor died while riding it:
http://motorcyclemuseum.org/classics/bike.asp?id=3

Movie with exciting sound track of a Roper replica chugging along:
http://www.lindsaybks.com/gallery/Jorg/cycle/Jorgbike.mov

Cheers,

Carl Fogel

[SMS]

Jay Beattie wrote:

> My cables boil! I was thinking of friction material fade. I totally
> glossed over the brake fluid boiling issue. It would seem to me that
> you could divert brake fluid heat in to a radiant loop to power a
> steam generator for the ride up the other side of the hill.

I use the steam to power a generator that operates by lights.

[Ben Kaufman]

On Fri, 28 Mar 2008 12:47:50 -0700, SMS <scharf.steven@geemail.com> wrote:

>Ben Kaufman wrote:
>> Is it normal to have blow-outs on a road bike from prolonged hard braking going
>> about one mile down a steep hill or should superior wheels and tires be able
>> to deal with the generated heat?
>
>It's normal. Pump your brakes rather than having them on all the time,
>and stop occasionally to let them cool. That said, it does vary with rim
>and tires. It's not the air in the tube expanding because of the heat
>that causes the blow out, it's the rim getting too hot.
>
>Are your rims straight side or hook edge? What kind of bead does the GT2
>tire have (steel or kevlar)? Sheldon's shop sells some 27" steel bead
>tires. See "http://www.sheldonbrown.com/harris/tires/630.html"

Wow, I see they do still have some name brand 27" tires. Thanks.
>
My rims are straight. The tire has a wire bead, I just checked the specs.
When I get them from performance they were "folded" but they spring back when
unleashed. The tires that my LBS put on were terrible. I think they were Kenda
brand and they would unseat and blow without provocation.


>Also, for a good and amusing tutorial by Sheldon about folding steel
>bead tires, see "http://www.sheldonbrown.com/video/tire-folding.html".
>Remember, red is the only color that works, LOL.
>
>On tandems, there was (or is) often a drum brake to use as a drag break
>when descending steep hills. A disc brake doesn't work well as a drag
>brake, as the rotor will warp and the pad will quickly be worn down.
>
> I have an old panasonic but keep the tires and
>> tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
>> not the best in the world but a heck of a lot better than what my LBS sold me.
>> It is a 27 inch rim and I could not find any better quality tires). But is it
>> the tire/wheel quality at issue? I have been thinking about getting a new bike
>> rather than trying to upgrade this one for a number of reasons (I don't think
>> it's even possible to switch to the current wheel size) but the blow-outs are
>> my biggest justification of expenditure to my wife.
>
>It's a good justification. Get a road bike with disc brakes. It will
>eliminate the blow outs, but if you ride with the brakes constantly on
>you'll go through a lot of pads and rotors.

I didn't know they made road bikes with disk brakes, I was thinking of something
like a Giant OCR C3..hmm I will have to look around some more. It is only this
one steep hill that gives me problems because of the hazards that I must keep
speed down, and of course I tend to keep it braking even harder for fear of
going too fast if I do have a blow out. My assumption, based upon the square of
velocity for kinetic energy is that it would generate less heat if I kept the
speed down to 10mph rather than 20mph (i would be going close to 50 mph without
braking).

Ben

[Garry Lee]

I've had about 3 such blowoffs. One in Gran Canaria, one on the
descent from Neuschwannstein Castle in Germany and one somewhere in
Ireland. Can't remember where.

[Michael Press]

In article <19hsu35n17mk38m2nujoqtghutpv8s88kf@4ax.com>,
Ben Kaufman <spaXm-mXe-anXd-paXy-5000-dollars@pobox.com> wrote:

> On Fri, 28 Mar 2008 12:47:50 -0700, SMS <scharf.steven@geemail.com> wrote:
>
> >Ben Kaufman wrote:
> >> Is it normal to have blow-outs on a road bike from prolonged hard braking going
> >> about one mile down a steep hill or should superior wheels and tires be able
> >> to deal with the generated heat?
> >
> >It's normal. Pump your brakes rather than having them on all the time,
> >and stop occasionally to let them cool. That said, it does vary with rim
> >and tires. It's not the air in the tube expanding because of the heat
> >that causes the blow out, it's the rim getting too hot.
> >
> >Are your rims straight side or hook edge? What kind of bead does the GT2
> >tire have (steel or kevlar)? Sheldon's shop sells some 27" steel bead
> >tires. See "http://www.sheldonbrown.com/harris/tires/630.html"
>
> Wow, I see they do still have some name brand 27" tires. Thanks.
> >
> My rims are straight. The tire has a wire bead, I just checked the specs.
> When I get them from performance they were "folded" but they spring back when
> unleashed. The tires that my LBS put on were terrible. I think they were Kenda
> brand and they would unseat and blow without provocation.
>
>
> >Also, for a good and amusing tutorial by Sheldon about folding steel
> >bead tires, see "http://www.sheldonbrown.com/video/tire-folding.html".
> >Remember, red is the only color that works, LOL.
> >
> >On tandems, there was (or is) often a drum brake to use as a drag break
> >when descending steep hills. A disc brake doesn't work well as a drag
> >brake, as the rotor will warp and the pad will quickly be worn down.
> >
> > I have an old panasonic but keep the tires and
> >> tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
> >> not the best in the world but a heck of a lot better than what my LBS sold me.
> >> It is a 27 inch rim and I could not find any better quality tires). But is it
> >> the tire/wheel quality at issue? I have been thinking about getting a new bike
> >> rather than trying to upgrade this one for a number of reasons (I don't think
> >> it's even possible to switch to the current wheel size) but the blow-outs are
> >> my biggest justification of expenditure to my wife.
> >
> >It's a good justification. Get a road bike with disc brakes. It will
> >eliminate the blow outs, but if you ride with the brakes constantly on
> >you'll go through a lot of pads and rotors.
>
> I didn't know they made road bikes with disk brakes, I was thinking of something
> like a Giant OCR C3..hmm I will have to look around some more. It is only this
> one steep hill that gives me problems because of the hazards that I must keep
> speed down, and of course I tend to keep it braking even harder for fear of
> going too fast if I do have a blow out. My assumption, based upon the square of
> velocity for kinetic energy is that it would generate less heat if I kept the
> speed down to 10mph rather than 20mph (i would be going close to 50 mph without
> braking).

Best to get going fast so that convective cooling is greatest.
Convective cooling increases linearly with temperature difference
and much more rapidly than linearly with speed.

Get up to high speed, brake rapidly to low speed. Stop altogether
if you feel hinky. On a regular route you could stop at different
times and check rim temperature. Use the _back_ of you hand, and
swipe it across the rim.

--
Michael Press

[jobst.brandt@stanfordalumni.org]

Ben Kaufman wrote:

>>> Is it normal to have blow-outs on a road bike from prolonged hard
>>> braking going about one mile down a steep hill or should superior
>>> wheels and tires be able to deal with the generated heat? I have
>>> an old Panasonic but keep the tires and tubes up to date
>>> (Performance Bike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
>>> not the best in the world but a heck of a lot better than what my
>>> LBS sold me. It is a 27 inch rim and I could not find any better
>>> quality tires). But is it the tire/wheel quality at issue? I
>>> have been thinking about getting a new bike rather than trying to
>>> upgrade this one for a number of reasons (I don't think it's even
>>> possible to switch to the current wheel size) but the blow-outs
>>> are my biggest justification of expenditure to my wife.

>> This is a traditional problem, so much so that bicycles are
>> prohibited down certain roads in the Alps. Zirlerberg above
>> Innsbruck is a classic with six runaway escape ramps for brake
>> failures of trucks. The Würzen Pass from Slovenia to Austria has a
>> long 18% grade.

>> Locally in the Santa Clara Valley we have several tire blow-off
>> descents on Metcalf Road and Hicks and Almaden Roads, each of which
>> has had fatalities on descents. Tandems are noted for this
>> problem, especially if the driver isn't careful to use front and
>> rear brakes equally. For this reason tandems used for mountain
>> touring are best equipped with hub brakes (drums or disks).

>> In the days of tubular tires, that were glued onto rims, glue
>> melted allowing tires to creep and tear off the inflation stem
>> causing rapid deflation. I experienced that effect in the alps ans
>> later had clincher blow-offs on the same stretch of the Gotthard
>> Pass.

>> I instrumented a wheel with pressure sensor and temperature
>> thermocouple to monitor a blow-off but was unsuccessful getting the
>> tire to separate even though temperature reached 150 degC and
>> pressure 125 psi. The mechanism for blow-off is still unclear but
>> it seams the bead material softens and creeps of the hooked bead of
>> the rim.

>> On steep descents after riding through water, I have generated
>> steam that came hissing out of the rim from around the stem as I
>> braked for successive hairpin turns on the Nufenen Pass in the
>> Alps.

> Darn, I may just have to avoid this hill in warmer weather :-)

I didn't mention it but this was with tubular tires on socketed rims,
so a rim strip had no part in this. Evaporative cooling is so fast
that as soon as the brake was released, the hissing steam ceased. At
first I thought I had a puncture and I was hearing air escaping from
the tire.

The lesson learned here is that there is much kinetic energy going
into the rim from braking. That it can produce steam reveals how hot
rims become even in cold weather. Water got into the rim crossing the
San Giacomo pass walking and sliding in deep snow and crossing a creek
to get on the plowed Nufenen Pass, the San Giacomo pass was still
snowed shut from winter.

http://www.goyellow.de/map/?lon=8.38788&lat=46.47754&z=14&mt=aerial

Passo della Novena := Nufenen Pass

Jobst Brandt

[Ben Kaufman]

On Sat, 29 Mar 2008 12:21:05 -0700 (PDT), datakoll <datakoll@yahoo.com> wrote:

>On Mar 27, 10:06*pm, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-
>doll...@pobox.com> wrote:
>> Is it normal to have blow-outs on a road bike from prolonged hard braking going
>> about one mile down *a *steep hill *or should superior wheels and tires be able
>> to deal with the generated heat? *I have an old panasonic but keep the tires and
>> tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, *which are
>> not the best in the world but *a heck of a lot better than what my LBS sold me.
>> It is a *27 inch rim and I could not find any better quality tires). *But is it
>> the tire/wheel quality at issue? *I have been thinking about getting a new bike
>> rather than trying to *upgrade this one for a number of reasons (I don't think
>> it's even possible to switch to the current wheel size) but *the blow-outs are
>> my biggest justification of expenditure to my wife.
>>
>> Thanks.
>>
>> Ben
>
>How many times do you bake from X to Y ? and how long are the times
>from braking point A to BP B?

This is a continuous downhill slope for about 1 mile. To keep my speed at about
10mph braking is continuous using a pulsing technique. The longest the brakes
are off is about (roughly) 5 seconds. At the steepest part they are off for
perhaps 1 second.
>
>I wrote the following last night. Sidewall dirt at the bead is
>relatively invisible under normal shop conditions.
>a thorough all surfaces cleaning before reassembly helps (and before
>disassembly) then pull and push nipple in and out to seat and pinch
>pinch pinch sidewalls inward thoroughly all around before and then
>maybe during the first pounds going in.
>once in a while when placing a new tube in, I'll soap, soak and brush
>sidewalls clean. I cover the sidewalls with FL teflon wax on the bead
>then overspray the area with belt conditioner as brake prep so the
>dirt is on that surface, floats away when soaping. after it gets
>beaten with a stick.

How does dirt on the bead and lubricating the bead help avoid this type of
blow-out? Wouldn't a lubricant actually make it easier for a tube bubble to
get around the bead?

Ben

[Tom Sherman]

datakoll aka gene daniels wrote:
>
> btw. BEN, do you know what reconditioned Panasonics are fetching on
> Ebay?

$795 for a 2007 "packable" Panasonic touring frameset, including
headset, fenders and racks: <http://www.yellowjersey.org/posd7.html>?

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Ben Kaufman]

On Sat, 29 Mar 2008 12:40:24 -0700 (PDT), datakoll <datakoll@yahoo.com> wrote:

>On Mar 27, 10:06*pm, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-
>doll...@pobox.com> wrote:
>> Is it normal to have blow-outs on a road bike from prolonged hard braking going
>> about one mile down *a *steep hill *or should superior wheels and tires be able
>> to deal with the generated heat? *I have an old panasonic but keep the tires and
>> tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, *which are
>> not the best in the world but *a heck of a lot better than what my LBS sold me.
>> It is a *27 inch rim and I could not find any better quality tires). *But is it
>> the tire/wheel quality at issue? *I have been thinking about getting a new bike
>> rather than trying to *upgrade this one for a number of reasons (I don't think
>> it's even possible to switch to the current wheel size) but *the blow-outs are
>> my biggest justification of expenditure to my wife.
>>
>> Thanks.
>>
>> Ben
>
>btw. BEN, do you know what reconditioned Panasonics are fetching on
>Ebay?

No idea. I have two of them. While mine can pass for heavily used my wife's
(sport - model below mine) has about 25 miles and the original Panasonic brand
tires.

Ben

[Ben Kaufman]

On Sat, 29 Mar 2008 13:06:22 -0700, Michael Press <rubrum@pacbell.net> wrote:

>In article <19hsu35n17mk38m2nujoqtghutpv8s88kf@4ax.com>,
> Ben Kaufman <spaXm-mXe-anXd-paXy-5000-dollars@pobox.com> wrote:
>
>> On Fri, 28 Mar 2008 12:47:50 -0700, SMS <scharf.steven@geemail.com> wrote:
>>
>> >Ben Kaufman wrote:
>> >> Is it normal to have blow-outs on a road bike from prolonged hard braking going
>> >> about one mile down a steep hill or should superior wheels and tires be able
>> >> to deal with the generated heat?
>> >
>> >It's normal. Pump your brakes rather than having them on all the time,
>> >and stop occasionally to let them cool. That said, it does vary with rim
>> >and tires. It's not the air in the tube expanding because of the heat
>> >that causes the blow out, it's the rim getting too hot.
>> >
>> >Are your rims straight side or hook edge? What kind of bead does the GT2
>> >tire have (steel or kevlar)? Sheldon's shop sells some 27" steel bead
>> >tires. See "http://www.sheldonbrown.com/harris/tires/630.html"
>>
>> Wow, I see they do still have some name brand 27" tires. Thanks.
>> >
>> My rims are straight. The tire has a wire bead, I just checked the specs.
>> When I get them from performance they were "folded" but they spring back when
>> unleashed. The tires that my LBS put on were terrible. I think they were Kenda
>> brand and they would unseat and blow without provocation.
>>
>>
>> >Also, for a good and amusing tutorial by Sheldon about folding steel
>> >bead tires, see "http://www.sheldonbrown.com/video/tire-folding.html".
>> >Remember, red is the only color that works, LOL.
>> >
>> >On tandems, there was (or is) often a drum brake to use as a drag break
>> >when descending steep hills. A disc brake doesn't work well as a drag
>> >brake, as the rotor will warp and the pad will quickly be worn down.
>> >
>> > I have an old panasonic but keep the tires and
>> >> tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
>> >> not the best in the world but a heck of a lot better than what my LBS sold me.
>> >> It is a 27 inch rim and I could not find any better quality tires). But is it
>> >> the tire/wheel quality at issue? I have been thinking about getting a new bike
>> >> rather than trying to upgrade this one for a number of reasons (I don't think
>> >> it's even possible to switch to the current wheel size) but the blow-outs are
>> >> my biggest justification of expenditure to my wife.
>> >
>> >It's a good justification. Get a road bike with disc brakes. It will
>> >eliminate the blow outs, but if you ride with the brakes constantly on
>> >you'll go through a lot of pads and rotors.
>>
>> I didn't know they made road bikes with disk brakes, I was thinking of something
>> like a Giant OCR C3..hmm I will have to look around some more. It is only this
>> one steep hill that gives me problems because of the hazards that I must keep
>> speed down, and of course I tend to keep it braking even harder for fear of
>> going too fast if I do have a blow out. My assumption, based upon the square of
>> velocity for kinetic energy is that it would generate less heat if I kept the
>> speed down to 10mph rather than 20mph (i would be going close to 50 mph without
>> braking).
>
>Best to get going fast so that convective cooling is greatest.
>Convective cooling increases linearly with temperature difference
>and much more rapidly than linearly with speed.
>
>Get up to high speed, brake rapidly to low speed. Stop altogether
>if you feel hinky. On a regular route you could stop at different
>times and check rim temperature. Use the _back_ of you hand, and
>swipe it across the rim.

Unfortunately, I have to keep the speed down on this particular hill due to the
curves, unpredictability of cars and road debris, including fallen rock. It is
also so steep that coasting speed gets back up very quickly so there is little
time before I have to reapply the brakes, especially towards the bottom where it
is steepest and there is the greatest danger of cars blowing a stop sign.
However, I do what you suggest on another hill (Harriman St. Park, NY) where I
can coast up to 40mph and not have to worry about anything (other than a crazy
deer) until a hairpin turn and then back up hill.

Ben

[datakoll]

Tom, do you work for the State?

[Tom Sherman]

datakoll aka gene daniels wrote:
>
> Tom, do you work for the State?

I do not have the connections to even get interviewed for a government job.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Hank]

On Mar 29, 6:06 pm, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-
doll...@pobox.com> wrote:
> On Sat, 29 Mar 2008 12:21:05 -0700 (PDT), datakoll <datak...@yahoo.com> wrote:
> >On Mar 27, 10:06 pm, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-
> >doll...@pobox.com> wrote:
> >> Is it normal to have blow-outs on a road bike from prolonged hard braking going
> >> about one mile down a steep hill or should superior wheels and tires be able
> >> to deal with the generated heat? I have an old panasonic but keep the tires and
> >> tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
> >> not the best in the world but a heck of a lot better than what my LBS sold me.
> >> It is a 27 inch rim and I could not find any better quality tires). But is it
> >> the tire/wheel quality at issue? I have been thinking about getting a new bike
> >> rather than trying to upgrade this one for a number of reasons (I don't think
> >> it's even possible to switch to the current wheel size) but the blow-outs are
> >> my biggest justification of expenditure to my wife.
>
> >> Thanks.
>
> >> Ben
>
> >How many times do you bake from X to Y ? and how long are the times
> >from braking point A to BP B?
>
> This is a continuous downhill slope for about 1 mile. To keep my speed at about
> 10mph braking is continuous using a pulsing technique. The longest the brakes
> are off is about (roughly) 5 seconds. At the steepest part they are off for
> perhaps 1 second.
>
>
>
> >I wrote the following last night. Sidewall dirt at the bead is
> >relatively invisible under normal shop conditions.
> >a thorough all surfaces cleaning before reassembly helps (and before
> >disassembly) then pull and push nipple in and out to seat and pinch
> >pinch pinch sidewalls inward thoroughly all around before and then
> >maybe during the first pounds going in.
> >once in a while when placing a new tube in, I'll soap, soak and brush
> >sidewalls clean. I cover the sidewalls with FL teflon wax on the bead
> >then overspray the area with belt conditioner as brake prep so the
> >dirt is on that surface, floats away when soaping. after it gets
> >beaten with a stick.
>
> How does dirt on the bead and lubricating the bead help avoid this type of
> blow-out? Wouldn't a lubricant actually make it easier for a tube bubble to
> get around the bead?
>
> Ben

Why 10mph? Even if it's winding, surely 15 doesn't seem too out of the
realm of sanity, IMO. I guess I'd have to see the road before passing
judgment on that, but 10mph just seems you're trading one danger for
another, if you're having frequent blowouts.

[A Muzi]

>> Ben Kaufman <spaXm-mXe-anXd-paXy-5000-doll...@pobox.com> wrote:
>>> Is it normal to have blow-outs on a road bike from prolonged hard braking going
>>> about one mile down a steep hill or should superior wheels and tires be able
>>> to deal with the generated heat? I have an old panasonic but keep the tires and
>>> tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
>>> not the best in the world but a heck of a lot better than what my LBS sold me.
>>> It is a 27 inch rim and I could not find any better quality tires). But is it
>>> the tire/wheel quality at issue? I have been thinking about getting a new bike
>>> rather than trying to upgrade this one for a number of reasons (I don't think
>>> it's even possible to switch to the current wheel size) but the blow-outs are
>>> my biggest justification of expenditure to my wife.

> datakoll <datakoll@yahoo.com> wrote:
>> How many times do you bake from X to Y ? and how long are the times
>>from braking point A to BP B?

Ben Kaufman wrote:
> This is a continuous downhill slope for about 1 mile. To keep my speed at about
> 10mph braking is continuous using a pulsing technique. The longest the brakes
> are off is about (roughly) 5 seconds. At the steepest part they are off for
> perhaps 1 second.

>> I wrote the following last night. Sidewall dirt at the bead is
>> relatively invisible under normal shop conditions.
>> a thorough all surfaces cleaning before reassembly helps (and before
>> disassembly) then pull and push nipple in and out to seat and pinch
>> pinch pinch sidewalls inward thoroughly all around before and then
>> maybe during the first pounds going in.
>> once in a while when placing a new tube in, I'll soap, soak and brush
>> sidewalls clean. I cover the sidewalls with FL teflon wax on the bead
>> then overspray the area with belt conditioner as brake prep so the
>> dirt is on that surface, floats away when soaping. after it gets
>> beaten with a stick.

Ben Kaufman wrote:
> How does dirt on the bead and lubricating the bead help avoid this type of
> blow-out? Wouldn't a lubricant actually make it easier for a tube bubble to
> get around the bead?

Unless something's awry with your particular equipment (torn tire,
dented rim), a nondestructive lubricant just makes proper, even seating
quicker. Car shops use soapy water on a brush which works equally well,
albeit messy. Once the tire is mounted straight, the manufacturer's
pressure ratings become relevant; If uneven, tires will creep over the edge.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

[Ben Kaufman]

On Sat, 29 Mar 2008 21:39:19 -0700 (PDT), Hank <hank@wirtznet.net> wrote:

>On Mar 29, 6:06 pm, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-
>doll...@pobox.com> wrote:
>> On Sat, 29 Mar 2008 12:21:05 -0700 (PDT), datakoll <datak...@yahoo.com> wrote:
>> >On Mar 27, 10:06 pm, Ben Kaufman <spaXm-mXe-anXd-paXy-5000-
>> >doll...@pobox.com> wrote:
>> >> Is it normal to have blow-outs on a road bike from prolonged hard braking going
>> >> about one mile down a steep hill or should superior wheels and tires be able
>> >> to deal with the generated heat? I have an old panasonic but keep the tires and
>> >> tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
>> >> not the best in the world but a heck of a lot better than what my LBS sold me.
>> >> It is a 27 inch rim and I could not find any better quality tires). But is it
>> >> the tire/wheel quality at issue? I have been thinking about getting a new bike
>> >> rather than trying to upgrade this one for a number of reasons (I don't think
>> >> it's even possible to switch to the current wheel size) but the blow-outs are
>> >> my biggest justification of expenditure to my wife.
>>
>> >> Thanks.
>>
>> >> Ben
>>
>> >How many times do you bake from X to Y ? and how long are the times
>> >from braking point A to BP B?
>>
>> This is a continuous downhill slope for about 1 mile. To keep my speed at about
>> 10mph braking is continuous using a pulsing technique. The longest the brakes
>> are off is about (roughly) 5 seconds. At the steepest part they are off for
>> perhaps 1 second.
>>
>>
>>
>> >I wrote the following last night. Sidewall dirt at the bead is
>> >relatively invisible under normal shop conditions.
>> >a thorough all surfaces cleaning before reassembly helps (and before
>> >disassembly) then pull and push nipple in and out to seat and pinch
>> >pinch pinch sidewalls inward thoroughly all around before and then
>> >maybe during the first pounds going in.
>> >once in a while when placing a new tube in, I'll soap, soak and brush
>> >sidewalls clean. I cover the sidewalls with FL teflon wax on the bead
>> >then overspray the area with belt conditioner as brake prep so the
>> >dirt is on that surface, floats away when soaping. after it gets
>> >beaten with a stick.
>>
>> How does dirt on the bead and lubricating the bead help avoid this type of
>> blow-out? Wouldn't a lubricant actually make it easier for a tube bubble to
>> get around the bead?
>>
>> Ben
>
>Why 10mph? Even if it's winding, surely 15 doesn't seem too out of the
>realm of sanity, IMO. I guess I'd have to see the road before passing
>judgment on that, but 10mph just seems you're trading one danger for
>another, if you're having frequent blowouts.

I could handle the road at 20 mph but my assumption has been that higher speeds
generate greater rim temperatures due to the square of the velocity for the
kinetic energy formula. If the hill wasn't so steep then taking it faster would
probably require a lot less use of the brakes but based upon other safer hills
that take me to about 40 mph, I would say this should be a significantly faster
decent.

Ben

[sergio]

On Mar 31, 7:17 am, Bill Bushnell <mrb...@pobox.com> wrote:

> Perhaps you would consider repeating your test with incrementally more air
> pressure in your tire.

Obviously unecessary.
What matters is the ultimate, not the starting, pressure.

Sergio
Pisa

[Tom Sherman]

Bill Bushnell wrote:
> jobst.brandt@stanfordalumni.org wrote:
>> I instrumented a wheel with pressure sensor and temperature
>> thermocouple to monitor a blow-off but was unsuccessful getting the
>> tire to separate even though temperature reached 150 degC and pressure
>> 125 psi. The mechanism for blow-off is still unclear but it seams the
>> bead material softens and creeps of the hooked bead of the rim.
>
> I stopped getting blowoffs when I reduced cold inflation pressure from 85 to 75
> psi (Ritchey Tom Slick, 559x36 on Ritchey rim). I believe that the likelihood of
> blowoff may be especially sensitive to inflation pressure because even though
> I've been riding around lately with an extra 45 lbs. on the bike, I still don't
> get blowoffs, even on the roads where they are likely to occur (Hicks, Vista
> Verde/Ramona, etc.)
>

Any past blowoffs on the (ISO 406-mm?/451-mm?) front wheel?

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

[Bill Bushnell]

Bill Bushnell <mrbill@pobox.com> wrote:
> jobst.brandt@stanfordalumni.org wrote:
> > I instrumented a wheel with pressure sensor and temperature
> > thermocouple to monitor a blow-off but was unsuccessful getting the
> > tire to separate even though temperature reached 150 degC and pressure
> > 125 psi. The mechanism for blow-off is still unclear but it seams the
> > bead material softens and creeps of the hooked bead of the rim.

> I stopped getting blowoffs when I reduced cold inflation pressure from 85 to 75
> psi (Ritchey Tom Slick, 559x36 on Ritchey rim). I believe that the likelihood of
> blowoff may be especially sensitive to inflation pressure because even though
> I've been riding around lately with an extra 45 lbs. on the bike, I still don't
> get blowoffs, even on the roads where they are likely to occur (Hicks, Vista
> Verde/Ramona, etc.)

> Perhaps you would consider repeating your test with incrementally more air
> pressure in your tire.

One further thought. Shortly after I began inflating my tires to 75 psi and
observed no more blow offs, I switched from the tan wall version of the Tom Slick
to the black wall version. Could the black coating on the bead hold better to a
hot rim than the tan bead?

--
Bill Bushnell
http://pobox.com/~bushnell/

[Bill Bushnell]

sergio <servadio@df.unipi.it> wrote:
> On Mar 31, 7:17 am, Bill Bushnell <mrb...@pobox.com> wrote:

> > Perhaps you would consider repeating your test with incrementally more air
> > pressure in your tire.

> Obviously unecessary.
> What matters is the ultimate, not the starting, pressure.

Both are interesting. The cold pressure matters because it's something the user
can easily measure and set. I know that if I inflate my tire to no more than 75
psi I'm unlikely to have a blowoff on any local descent. This is useful
information.

Based on my own experience (1 sample), I found I no longer had blowoffs on my
particular tire/rim combination after reducing my cold inflation pressure from 85
to 75 psi. Even after I started carrying more weight on the bike, and presumably
generating more rim heat on the descents, I still did not get any blowoffs. Jobst
doesn't say what cold pressure he started with, but I'm suggesting that he might
yet achieve a blowoff if he were to start with more pressure in the tire.

--
Bill Bushnell
http://pobox.com/~bushnell/

[Michael Press]

In article <0qk1v3tc5btvkopmcg8s611eq3h0m5hai2@4ax.com>,
Ben Kaufman <spaXm-mXe-anXd-paXy-5000-dollars@pobox.com> wrote:

> On Sat, 29 Mar 2008 21:39:19 -0700 (PDT), Hank <hank@wirtznet.net> wrote:
> >Why 10mph? Even if it's winding, surely 15 doesn't seem too out of the
> >realm of sanity, IMO. I guess I'd have to see the road before passing
> >judgment on that, but 10mph just seems you're trading one danger for
> >another, if you're having frequent blowouts.
>
> I could handle the road at 20 mph but my assumption has been that higher speeds
> generate greater rim temperatures due to the square of the velocity for the
> kinetic energy formula. If the hill wasn't so steep then taking it faster would
> probably require a lot less use of the brakes but based upon other safer hills
> that take me to about 40 mph, I would say this should be a significantly faster
> decent.

I explained this several times. The amount of energy dissipated
is the same for a given descent and initial and terminal speeds.
Forget kinetic energy as a function of speed. Concentrate on
total energy dissipated. The goal is to reduce the heating of
the tire bead and the air in the tube. If the rim is always hot
as with constant braking you are guaranteed to heat the bead
an inflation air. If you allow for free runs downhill with no
braking, the rim will cool quickly, very much more quickly if
you allow the free runs to have maximum speed before braking.
Heavy braking decreases the amount of time to heat the rim.
Then you get off the brakes and allow the rim to cool. The
energy dissipation rate for a hot rim increases with the
temperature, so you are spending more time dissipating heat to
the air at a high rate; dissipating heat that will not go to
heating the bead and inflation air. Another thing you have not
considered is that when coasting downhill at speed you dissipate
more energy to wind drag the faster you go; the rate of dissipation
increases more than linearly with speed.

--
Michael Press

[Ben C]

On 2008-03-31, Michael Press <rubrum@pacbell.net> wrote:
> In article <0qk1v3tc5btvkopmcg8s611eq3h0m5hai2@4ax.com>,
> Ben Kaufman <spaXm-mXe-anXd-paXy-5000-dollars@pobox.com> wrote:
>
>> On Sat, 29 Mar 2008 21:39:19 -0700 (PDT), Hank <hank@wirtznet.net> wrote:
>> >Why 10mph? Even if it's winding, surely 15 doesn't seem too out of the
>> >realm of sanity, IMO. I guess I'd have to see the road before passing
>> >judgment on that, but 10mph just seems you're trading one danger for
>> >another, if you're having frequent blowouts.
>>
>> I could handle the road at 20 mph but my assumption has been that higher speeds
>> generate greater rim temperatures due to the square of the velocity for the
>> kinetic energy formula. If the hill wasn't so steep then taking it faster would
>> probably require a lot less use of the brakes but based upon other safer hills
>> that take me to about 40 mph, I would say this should be a significantly faster
>> decent.
>
> I explained this several times. The amount of energy dissipated
> is the same for a given descent and initial and terminal speeds.

Yes, but the rate at which it is dissipated (power) is not. I think Ben
has a point: braking power is minimized by descending as slowly as
possible, even though total braking energy will be higher (the air will
do less for you at a lower speed, and you will have less k.e. at the
bottom).

If the brakes are overheating, going slowly will help I think. Yes if
you get them hotter they will cool faster, but with rim brakes I suspect
that's a losing battle-- the temperature at which the tyres blow off is
not that high.

[Ben C]

On 2008-03-31, Michael Press <rubrum@pacbell.net> wrote:
> In article <0qk1v3tc5btvkopmcg8s611eq3h0m5hai2@4ax.com>,
> Ben Kaufman <spaXm-mXe-anXd-paXy-5000-dollars@pobox.com> wrote:
>
>> On Sat, 29 Mar 2008 21:39:19 -0700 (PDT), Hank <hank@wirtznet.net> wrote:
>> >Why 10mph? Even if it's winding, surely 15 doesn't seem too out of the
>> >realm of sanity, IMO. I guess I'd have to see the road before passing
>> >judgment on that, but 10mph just seems you're trading one danger for
>> >another, if you're having frequent blowouts.
>>
>> I could handle the road at 20 mph but my assumption has been that
>> higher speeds generate greater rim temperatures due to the square of
>> the velocity for the kinetic energy formula. If the hill wasn't so
>> steep then taking it faster would probably require a lot less use of
>> the brakes but based upon other safer hills that take me to about 40
>> mph, I would say this should be a significantly faster decent.
>
> I explained this several times. The amount of energy dissipated
> is the same for a given descent and initial and terminal speeds.

Yes. But the power at which the rim is heated and at which it cools is
not.

> Forget kinetic energy as a function of speed.

Why? It seems to me it is quite important.

> Concentrate on total energy dissipated. The goal is to reduce the
> heating of the tire bead and the air in the tube. If the rim is always
> hot as with constant braking you are guaranteed to heat the bead an
> inflation air.

If you heat the rim at the same rate at which it is also cooling, then
you're going to be all right aren't you?

> If you allow for free runs downhill with no braking, the rim will cool
> quickly, very much more quickly if you allow the free runs to have
> maximum speed before braking.

Yes. But it might not be safe to descend with no braking.

> Heavy braking decreases the amount of time to heat the rim.
> Then you get off the brakes and allow the rim to cool. The
> energy dissipation rate for a hot rim increases with the
> temperature, so you are spending more time dissipating heat to
> the air at a high rate; dissipating heat that will not go to
> heating the bead and inflation air.

I agree that non-continuous braking may help.

> Another thing you have not considered is that when coasting downhill
> at speed you dissipate more energy to wind drag the faster you go; the
> rate of dissipation increases more than linearly with speed.

This is all good advice, but it doesn't answer the question: is it
better to brake continuously to maintain 10mph or continuously to
maintain 20mph on a hill with a coasting speed of 50mph?

If my tyre blows off either way, do I get further before it blows off if
I go at 10mph or if I go at 20mph?

[Ben Kaufman]

On Mon, 31 Mar 2008 11:29:49 -0700, Michael Press <rubrum@pacbell.net> wrote:

>In article <0qk1v3tc5btvkopmcg8s611eq3h0m5hai2@4ax.com>,
> Ben Kaufman <spaXm-mXe-anXd-paXy-5000-dollars@pobox.com> wrote:
>
>> On Sat, 29 Mar 2008 21:39:19 -0700 (PDT), Hank <hank@wirtznet.net> wrote:
>> >Why 10mph? Even if it's winding, surely 15 doesn't seem too out of the
>> >realm of sanity, IMO. I guess I'd have to see the road before passing
>> >judgment on that, but 10mph just seems you're trading one danger for
>> >another, if you're having frequent blowouts.
>>
>> I could handle the road at 20 mph but my assumption has been that higher speeds
>> generate greater rim temperatures due to the square of the velocity for the
>> kinetic energy formula. If the hill wasn't so steep then taking it faster would
>> probably require a lot less use of the brakes but based upon other safer hills
>> that take me to about 40 mph, I would say this should be a significantly faster
>> decent.
>
>I explained this several times. The amount of energy dissipated
>is the same for a given descent and initial and terminal speeds.
>Forget kinetic energy as a function of speed. Concentrate on
>total energy dissipated. The goal is to reduce the heating of
>the tire bead and the air in the tube. If the rim is always hot
>as with constant braking you are guaranteed to heat the bead
>an inflation air. If you allow for free runs downhill with no
>braking, the rim will cool quickly, very much more quickly if
>you allow the free runs to have maximum speed before braking.
>Heavy braking decreases the amount of time to heat the rim.
>Then you get off the brakes and allow the rim to cool. The
>energy dissipation rate for a hot rim increases with the
>temperature, so you are spending more time dissipating heat to
>the air at a high rate; dissipating heat that will not go to
>heating the bead and inflation air. Another thing you have not
>considered is that when coasting downhill at speed you dissipate
>more energy to wind drag the faster you go; the rate of dissipation
>increases more than linearly with speed.

As I have explained in previous messages, I cannot to go very fast due to
concerns about cars.

Ben.

[Michael Press]

In article <slrnfv2cjf.hn7.spamspam@bowser.marioworld>,
Ben C <spamspam@spam.eggs> wrote:

> On 2008-03-31, Michael Press <rubrum@pacbell.net> wrote:
> > In article <0qk1v3tc5btvkopmcg8s611eq3h0m5hai2@4ax.com>,
> > Ben Kaufman <spaXm-mXe-anXd-paXy-5000-dollars@pobox.com> wrote:
> >
> >> On Sat, 29 Mar 2008 21:39:19 -0700 (PDT), Hank <hank@wirtznet.net> wrote:
> >> >Why 10mph? Even if it's winding, surely 15 doesn't seem too out of the
> >> >realm of sanity, IMO. I guess I'd have to see the road before passing
> >> >judgment on that, but 10mph just seems you're trading one danger for
> >> >another, if you're having frequent blowouts.
> >>
> >> I could handle the road at 20 mph but my assumption has been that higher speeds
> >> generate greater rim temperatures due to the square of the velocity for the
> >> kinetic energy formula. If the hill wasn't so steep then taking it faster would
> >> probably require a lot less use of the brakes but based upon other safer hills
> >> that take me to about 40 mph, I would say this should be a significantly faster
> >> decent.
> >
> > I explained this several times. The amount of energy dissipated
> > is the same for a given descent and initial and terminal speeds.
>
> Yes, but the rate at which it is dissipated (power) is not. I think Ben
> has a point: braking power is minimized by descending as slowly as
> possible, even though total braking energy will be higher (the air will
> do less for you at a lower speed, and you will have less k.e. at the
> bottom).
>
> If the brakes are overheating, going slowly will help I think. Yes if
> you get them hotter they will cool faster, but with rim brakes I suspect
> that's a losing battle-- the temperature at which the tyres blow off is
> not that high.

Why do you choose to silently excise the technical material in
the message to which you replied?

--
Michael Press

[carlfogel@comcast.net]

On Mar 31, 12:50*pm, Ben C <spams...@spam.eggs> wrote:
> On 2008-03-31, Michael Press <rub...@pacbell.net> wrote:
>
> > In article <0qk1v3tc5btvkopmcg8s611eq3h0m5h...@4ax.com>,
> > *Ben Kaufman <spaXm-mXe-anXd-paXy-5000-doll...@pobox.com> wrote:
>
> >> On Sat, 29 Mar 2008 21:39:19 -0700 (PDT), Hank <h...@wirtznet.net> wrote:
> >> >Why 10mph? Even if it's winding, surely 15 doesn't seem too out of the
> >> >realm of sanity, IMO. I guess I'd have to see the road before passing
> >> >judgment on that, but 10mph just seems you're trading one danger for
> >> >another, if you're having frequent blowouts.
>
> >> I could handle the road at 20 mph but my assumption has been that higher speeds
> >> generate greater rim temperatures due to the square of the velocity for the
> >> kinetic energy formula. *If the hill wasn't so steep then taking it faster would
> >> probably require a lot less use of the brakes but based upon other safer *hills
> >> that take me to about 40 mph, I would say this should be a significantly *faster
> >> decent. *
>
> > I explained this several times. The amount of energy dissipated
> > is the same for a given descent and initial and terminal speeds.
>
> Yes, but the rate at which it is dissipated (power) is not. I think Ben
> has a point: braking power is minimized by descending as slowly as
> possible, even though total braking energy will be higher (the air will
> do less for you at a lower speed, and you will have less k.e. at the
> bottom).
>
> If the brakes are overheating, going slowly will help I think. Yes if
> you get them hotter they will cool faster, but with rim brakes I suspect
> that's a losing battle-- the temperature at which the tyres blow off is
> not that high

Dear Ben,

A few years ago, I wondered about fixie braking downhill.

On the same hill, the braking watts needed to maintain a particular
speed rise and fall in a curve, up from 0 watts at a standstill (no
movement) to a maximum value and then back to 0 watts again at top
speed (no braking).

For a 40 mph coasting-speed hill, the peak of the braking power curve
was around 23 mph. Faster or slower than 23 mph meant less braking
effort. It would take considerable (and impractical) calculations to
discover which two points on either side of the peak of the curve
correspond to each other.

That is, for 15 mph on the hill, the same braking power is needed at
some speed between 23 mph and 40 mph, but the precise speed is not
practical.

Here's where Peter Cole cleared things up:
http://groups.google.com/group/rec.bicycles.tech/msg/20e679ab31dbf07d

Even going very slowly, Jobst blew a tire off. I did the same thing,
even though I'd read his post:

http://groups.google.com/group/rec.bicycles.tech/msg/e7b83b9ccefa849f

Cheers,

Carl Fogel

[Ben Kaufman]

On Mon, 31 Mar 2008 13:50:08 -0500, Ben C <spamspam@spam.eggs> wrote:

>On 2008-03-31, Michael Press <rubrum@pacbell.net> wrote:
>> In article <0qk1v3tc5btvkopmcg8s611eq3h0m5hai2@4ax.com>,
>> Ben Kaufman <spaXm-mXe-anXd-paXy-5000-dollars@pobox.com> wrote:
>>
>>> On Sat, 29 Mar 2008 21:39:19 -0700 (PDT), Hank <hank@wirtznet.net> wrote:
>>> >Why 10mph? Even if it's winding, surely 15 doesn't seem too out of the
>>> >realm of sanity, IMO. I guess I'd have to see the road before passing
>>> >judgment on that, but 10mph just seems you're trading one danger for
>>> >another, if you're having frequent blowouts.
>>>
>>> I could handle the road at 20 mph but my assumption has been that higher speeds
>>> generate greater rim temperatures due to the square of the velocity for the
>>> kinetic energy formula. If the hill wasn't so steep then taking it faster would
>>> probably require a lot less use of the brakes but based upon other safer hills
>>> that take me to about 40 mph, I would say this should be a significantly faster
>>> decent.
>>
>> I explained this several times. The amount of energy dissipated
>> is the same for a given descent and initial and terminal speeds.
>
>Yes, but the rate at which it is dissipated (power) is not. I think Ben
>has a point: braking power is minimized by descending as slowly as
>possible, even though total braking energy will be higher (the air will
>do less for you at a lower speed, and you will have less k.e. at the
>bottom).
>
>If the brakes are overheating, going slowly will help I think. Yes if
>you get them hotter they will cool faster, but with rim brakes I suspect
>that's a losing battle-- the temperature at which the tyres blow off is
>not that high.

Next time I am going to try 5mph. I am game for anything that will get me to
crash slower.

Ben

[Ben C]

On 2008-03-31, Michael Press <rubrum@pacbell.net> wrote:
> In article <slrnfv2cjf.hn7.spamspam@bowser.marioworld>,
> Ben C <spamspam@spam.eggs> wrote:
>
>> On 2008-03-31, Michael Press <rubrum@pacbell.net> wrote:
>> > In article <0qk1v3tc5btvkopmcg8s611eq3h0m5hai2@4ax.com>,
>> > Ben Kaufman <spaXm-mXe-anXd-paXy-5000-dollars@pobox.com> wrote:
>> >
>> >> On Sat, 29 Mar 2008 21:39:19 -0700 (PDT), Hank <hank@wirtznet.net> wrote:
>> >> >Why 10mph? Even if it's winding, surely 15 doesn't seem too out of the
>> >> >realm of sanity, IMO. I guess I'd have to see the road before passing
>> >> >judgment on that, but 10mph just seems you're trading one danger for
>> >> >another, if you're having frequent blowouts.
>> >>
>> >> I could handle the road at 20 mph but my assumption has been that higher speeds
>> >> generate greater rim temperatures due to the square of the velocity for the
>> >> kinetic energy formula. If the hill wasn't so steep then taking it faster would
>> >> probably require a lot less use of the brakes but based upon other safer hills
>> >> that take me to about 40 mph, I would say this should be a significantly faster
>> >> decent.
>> >
>> > I explained this several times. The amount of energy dissipated
>> > is the same for a given descent and initial and terminal speeds.
>>
>> Yes, but the rate at which it is dissipated (power) is not. I think Ben
>> has a point: braking power is minimized by descending as slowly as
>> possible, even though total braking energy will be higher (the air will
>> do less for you at a lower speed, and you will have less k.e. at the
>> bottom).
>>
>> If the brakes are overheating, going slowly will help I think. Yes if
>> you get them hotter they will cool faster, but with rim brakes I suspect
>> that's a losing battle-- the temperature at which the tyres blow off is
>> not that high.
>
> Why do you choose to silently excise the technical material in
> the message to which you replied?

I often excise material if it doesn't seem relevant to the particular
quibble I am making.

But since you mention it, I have just posted another followup with no
snipping which I hope will be clearer.

[Ben C]

On 2008-03-31, carlfogel@comcast.net <carlfogel@comcast.net> wrote:
> On Mar 31, 12:50*pm, Ben C <spams...@spam.eggs> wrote:
[...]
>> Yes, but the rate at which it is dissipated (power) is not. I think Ben
>> has a point: braking power is minimized by descending as slowly as
>> possible, even though total braking energy will be higher (the air will
>> do less for you at a lower speed, and you will have less k.e. at the
>> bottom).
>>
>> If the brakes are overheating, going slowly will help I think. Yes if
>> you get them hotter they will cool faster, but with rim brakes I suspect
>> that's a losing battle-- the temperature at which the tyres blow off is
>> not that high
>
> Dear Ben,
>
> A few years ago, I wondered about fixie braking downhill.
>
> On the same hill, the braking watts needed to maintain a particular
> speed rise and fall in a curve, up from 0 watts at a standstill (no
> movement) to a maximum value and then back to 0 watts again at top
> speed (no braking).
>
> For a 40 mph coasting-speed hill, the peak of the braking power curve
> was around 23 mph. Faster or slower than 23 mph meant less braking
> effort. It would take considerable (and impractical) calculations to
> discover which two points on either side of the peak of the curve
> correspond to each other.
>
> That is, for 15 mph on the hill, the same braking power is needed at
> some speed between 23 mph and 40 mph, but the precise speed is not
> practical.
>
> Here's where Peter Cole cleared things up:
> http://groups.google.com/group/rec.bicycles.tech/msg/20e679ab31dbf07d
>
> Even going very slowly, Jobst blew a tire off. I did the same thing,
> even though I'd read his post:
>
> http://groups.google.com/group/rec.bicycles.tech/msg/e7b83b9ccefa849f

Thanks for the links. From what I can understand of that, the 23mph peak
arises because of wind drag. If you go faster you get more help from the
wind. But if you go slower, you are dumping the given amount of
gravitational potential energy you have into the brakes at a lower rate,
which helps them not to get so hot.

The OP's hill is good for 50mph coasting-speed and he's talking about
going 10mph rather than 20mph. I think he might be better off at 10mph,
although he might be doomed either way (see below).

You overheated a wheel descending at 10mph, but would the situation have
been better at 20mph? It depends on the hill-- if it was very steep,
10mph might have been better than 20mph.

But there is one factor I'm not sure of here, which is the rate of
cooling of a rim. The fastest you can safely descend (given that you
want to be on the slow side of the peak) is the speed at which the rim
can remain constantly at the temperature just below that required to
give you tyre problems. In other words the speed at which which braking
power is equal to cooling power.

You can also ask what's the slowest speed at which you can stably
descend while being on the fast side of the peak. But if the peak is too
fast for safety, then you'll have to choose the slow side.

There is a slow and a fast stable descending speed for any given
indefinitely long hill and given bike+rider mass. I suspect that the
slow stable descending speed is rather low, but I don't know what it is.

If you go faster than the slow stable speed (but less than the peak, or
slower than the fast stable speed but faster than the peak) then it's
only a matter of time before heat builds up to dangerous levels. So it
depends how long the hill goes on for.

It would be interesting to know just what that the slow stable speed is
for a typical steep hill. It might be unreasonably slow, in which case
the OP is doomed unless the hill is short and will have to bite the
bullet and go at the fast stable speed, get disk brakes, or walk.

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/steam-engineering-principles-and-heat-transfer/heat-transfer.asp#head33

or

http://tinyurl.com/2vpv7v

describes a "general heat transfer equation" which looks quite easy to
deal with.

Does anyone know the "overall heat transfer coefficient" for aluminium
in air?

[Ben Kaufman]

On Mon, 31 Mar 2008 12:19:06 -0700 (PDT), carlfogel@comcast.net wrote:

>On Mar 31, 12:50*pm, Ben C <spams...@spam.eggs> wrote:
>> On 2008-03-31, Michael Press <rub...@pacbell.net> wrote:
>>
>> > In article <0qk1v3tc5btvkopmcg8s611eq3h0m5h...@4ax.com>,
>> > *Ben Kaufman <spaXm-mXe-anXd-paXy-5000-doll...@pobox.com> wrote:
>>
>> >> On Sat, 29 Mar 2008 21:39:19 -0700 (PDT), Hank <h...@wirtznet.net> wrote:
>> >> >Why 10mph? Even if it's winding, surely 15 doesn't seem too out of the
>> >> >realm of sanity, IMO. I guess I'd have to see the road before passing
>> >> >judgment on that, but 10mph just seems you're trading one danger for
>> >> >another, if you're having frequent blowouts.
>>
>> >> I could handle the road at 20 mph but my assumption has been that higher speeds
>> >> generate greater rim temperatures due to the square of the velocity for the
>> >> kinetic energy formula. *If the hill wasn't so steep then taking it faster would
>> >> probably require a lot less use of the brakes but based upon other safer *hills
>> >> that take me to about 40 mph, I would say this should be a significantly *faster
>> >> decent. *
>>
>> > I explained this several times. The amount of energy dissipated
>> > is the same for a given descent and initial and terminal speeds.
>>
>> Yes, but the rate at which it is dissipated (power) is not. I think Ben
>> has a point: braking power is minimized by descending as slowly as
>> possible, even though total braking energy will be higher (the air will
>> do less for you at a lower speed, and you will have less k.e. at the
>> bottom).
>>