Crank ID req. on Singlespeed CX bike

[Kinky Cowboy]

Nice singlespeed CX bike here
http://img149.imagevenue.com/img.php?image=86313_Don_Cristina6_04_06LARGE_122_9 01lo.jpg

but what are the cranks? Look BMX-ish, and as far as I can see they're
a T-section beam. Odd.
Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary
** Posted from http://www.teranews.com **

[Chalo]

Kinky Cowboy wrote:
>
> Nice singlespeed CX bike here
>
> http://img149.imagevenue.com/img.php?image=86313_Don_Cristina6_04_06L...
>
> but what are the cranks? Look BMX-ish, and as far as I can see they're
> a T-section beam. Odd.

Those are taper-fitted cranks, not much like the BMX cranks I'm
familiar with. They look more reminiscent of CNC-era mountain bike
stuff.

Perhaps she used alkali to strip off the Rasta tricolor anodizing.

Structurally speaking, it would probably be better to load the web in
tension and the flat in compression. If she gets a left-hand drive
rear wheel, she'll be all sorted out.

Chalo

[James Thomson]

"Kinky Cowboy" <user@domain.com> a écrit:

> Nice singlespeed CX bike here
> http://img149.imagevenue.com/img.php?image=86313_Don_Cristina6_04_06LARGE_122_9 01lo.jpg
>
> but what are the cranks?

XLR8?:

http://www.retrobike.co.uk/forum/files/xlr8crank_631.jpg

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220227665875

James Thomson

[Kinky Cowboy]

On Tue, 22 Apr 2008 16:11:57 -0700 (PDT), Chalo
<chalo.colina@gmail.com> wrote:

>Kinky Cowboy wrote:
>>
>> Nice singlespeed CX bike here
>>
>> http://img149.imagevenue.com/img.php?image=86313_Don_Cristina6_04_06L...
>>
>> but what are the cranks? Look BMX-ish, and as far as I can see they're
>> a T-section beam. Odd.
>
>Those are taper-fitted cranks, not much like the BMX cranks I'm
>familiar with. They look more reminiscent of CNC-era mountain bike
>stuff.
>

BMX-ish in the sense of junior BMX kit, where aluminium alloy square
taper cranks are common. The fact that the spider is a: separate and
b: looks familiar from something I've seen on a BMX site also suggests
BMX rather than MTB origin.

The T section might be the wrong way round, but the mystery is why
it's a T instead of an H in the first place. The even bigger mystery
is why all cranks aren't tubular, like the BMX CroMo cranks you're
familiar with, as a crank is a torsion bar, not a beam :-)

Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary
** Posted from http://www.teranews.com **

[Kinky Cowboy]

On Wed, 21 May 2008 19:17:24 +0200, "James Thomson"
<yosnappyj@hotmail.com> wrote:

>"Kinky Cowboy" <user@domain.com> a ?crit:
>
>> Nice singlespeed CX bike here
>> http://img149.imagevenue.com/img.php?image=86313_Don_Cristina6_04_06LARGE_122_9 01lo.jpg
>>
>> but what are the cranks?
>
>XLR8?:
>
>http://www.retrobike.co.uk/forum/files/xlr8crank_631.jpg
>
>http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220227665875
>
>James Thomson
>

That would seem to be it. Thanks.
Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary
** Posted from http://www.teranews.com **

[jobst.brandt@stanfordalumni.org]

someone wrote:

>>> Nice singlespeed CX bike here

http://img149.imagevenue.com/img.php?image=86313_Don_Cristina6_04_06LARGE_122_9 01lo.jpg

>>> but what are the cranks?

>> XLR8?:

http://www.retrobike.co.uk/forum/files/xlr8crank_631.jpg

There is another excellent example of a finely finished product
designed by someone who doesn't understand the function. The largest
load cranks transmit is torsion from the outboard position of the foot
on the pedal, although in a side view is not apparent.

The crank is a lever that is loaded off axis so that its shaft has far
higher (about 5x) torsional stress than it has in lever bending.
Torsional strength is given by the largest inscribed circular cross
section of the lever, which in this model is tiny, all the flat and
flashy part being unstressed.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220227665875

> That would seem to be it. Thanks.

This has been a design problem that has caused many crank failures and
ultimately got Campagnolo to get rid of the vanity groove on the
outside of their cranks that cost them durability.

Jobst Brandt

[Kinky Cowboy]

On 22 May 2008 18:49:24 GMT, jobst.brandt@stanfordalumni.org wrote:

>someone wrote:
>
>>>> Nice singlespeed CX bike here
>
> http://img149.imagevenue.com/img.php?image=86313_Don_Cristina6_04_06LARGE_122_9 01lo.jpg
>
>>>> but what are the cranks?
>
>>> XLR8?:
>
> http://www.retrobike.co.uk/forum/files/xlr8crank_631.jpg
>
>There is another excellent example of a finely finished product
>designed by someone who doesn't understand the function. The largest
>load cranks transmit is torsion from the outboard position of the foot
>on the pedal, although in a side view is not apparent.
>
>The crank is a lever that is loaded off axis so that its shaft has far
>higher (about 5x) torsional stress than it has in lever bending.
>Torsional strength is given by the largest inscribed circular cross
>section of the lever, which in this model is tiny, all the flat and
>flashy part being unstressed.
>

True; I was interested in it as a curiosity, for actual riding it's
hard to beat tubular BMX cranks in a stiffness/weight showdown. The
853 ones on my MTB aren't even much heavier than a good forged
aluminium crankset, although the BB spindle is all but solid and has 4
bearings, so total weight is a bit porky.

Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary
** Posted from http://www.teranews.com **