pinch flats 180 degrees out of phase

[meb]

I recently hopped a curb from a parking lot to a paved trail into a
woods on a road bike-I mistook the curb for a ramp. I had 27x1 1/4 on
the front and 27 x 1 on the rear. In addition to the wider front, I
pulled up on the front handlebars to unload the front wheel whilst
traversing onto the trail. The rear received 2 pairs of pinch flats,
each pair of fang marks 180 degrees apart on the wheel. Any idea what
phenominon might pinch the tube twice?

i.e., might the rear have bounced or was something else likely going
on?


--
meb

[catzz66]

meb wrote:
> I recently hopped a curb from a parking lot to a paved trail into a
> woods on a road bike-I mistook the curb for a ramp. I had 27x1 1/4 on
> the front and 27 x 1 on the rear. In addition to the wider front, I
> pulled up on the front handlebars to unload the front wheel whilst
> traversing onto the trail. The rear received 2 pairs of pinch flats,
> each pair of fang marks 180 degrees apart on the wheel. Any idea what
> phenominon might pinch the tube twice?
>
> i.e., might the rear have bounced or was something else likely going
> on?
>
>

My guess would be that you may have just gotten lucky once before and
crimped the tube, but not enough to cause a failure. I top off my tires
every time I get ready to go out and still have hit some pretty mean
potholes that caused me to worry about pinch flats.

[carlfogel@comcast.net]

On Tue, 5 Feb 2008 19:53:11 +1100, meb
<meb.34aw30@no-mx.forums.cyclingforums.com> wrote:

>
>I recently hopped a curb from a parking lot to a paved trail into a
>woods on a road bike-I mistook the curb for a ramp. I had 27x1 1/4 on
>the front and 27 x 1 on the rear. In addition to the wider front, I
>pulled up on the front handlebars to unload the front wheel whilst
>traversing onto the trail. The rear received 2 pairs of pinch flats,
>each pair of fang marks 180 degrees apart on the wheel. Any idea what
>phenominon might pinch the tube twice?
>
>i.e., might the rear have bounced or was something else likely going
>on?

Dear Meb,

You could get a second pinch flat by hitting something a moment or two
after the first pinch flat let the air out of the tube.

A much smaller impact and obstacle can pinch the deflated tube.

Where the second pinch occurred would be pure chance.

Cheers,

Carl Fogel

[meb]

catzz66 Wrote:
> meb wrote:
> > I recently hopped a curb from a parking lot to a paved trail into a
> > woods on a road bike-I mistook the curb for a ramp. I had 27x1 1/4
> on
> > the front and 27 x 1 on the rear. In addition to the wider front, I
> > pulled up on the front handlebars to unload the front wheel whilst
> > traversing onto the trail. The rear received 2 pairs of pinch
> flats,
> > each pair of fang marks 180 degrees apart on the wheel. Any idea
> what
> > phenominon might pinch the tube twice?
> >
> > i.e., might the rear have bounced or was something else likely going
> > on?
> >
> >
>
> My guess would be that you may have just gotten lucky once before and
> crimped the tube, but not enough to cause a failure. I top off my
> tires
> every time I get ready to go out and still have hit some pretty mean
> potholes that caused me to worry about pinch flats.

An interesting hypothesis but I think I can rule this out via a repair
that would have made Laurel and Hardy proud. Seeing the first spotted
pair had one hole big enough as to let me fill the presta tube with
Slime, I elected to make the best of a bad situation and dumped a half
bottle of Slime in the tube before patching. The next day, I tested the
tube prior to replacing in the tire to see if the patch held. The patch
job held. However, the newly added Slime went shooting through my
kitchen via the opposite pair of holes I had not yet discovered. Both
pairs of pinches were open. Hence a thread I started elsewhere a few
weeks ago inquring about the effects of Slime on clothing.


--
meb

[meb]

carlfogel@comcast.net Wrote:
> On Tue, 5 Feb 2008 19:53:11 +1100, meb
> <meb.34aw30@no-mx.forums.cyclingforums.com> wrote:
>
> >
> >I recently hopped a curb from a parking lot to a paved trail into a
> >woods on a road bike-I mistook the curb for a ramp. I had 27x1 1/4
> on
> >the front and 27 x 1 on the rear. In addition to the wider front, I
> >pulled up on the front handlebars to unload the front wheel whilst
> >traversing onto the trail. The rear received 2 pairs of pinch flats,
> >each pair of fang marks 180 degrees apart on the wheel. Any idea
> what
> >phenominon might pinch the tube twice?
> >
> >i.e., might the rear have bounced or was something else likely going
> >on?
>
> Dear Meb,
>
> You could get a second pinch flat by hitting something a moment or two
> after the first pinch flat let the air out of the tube.
>
> A much smaller impact and obstacle can pinch the deflated tube.
>
> Where the second pinch occurred would be pure chance.
>
> Cheers,
>
> Carl Fogel

Beyond the curb the paved trail was pretty smooth. I wondered about
whether a deflated tube might be more vulnerable and hence inquired
about the possibility of a bounce. I suppose it might also a simple
spreading of the deflated tube over the rim prior to dismounting. The
hiss was so unmistakeable that I knew the tube was flat and quickly
dismounted, though perhaps not quick enough. It's a steep uphill
climb, I think I've only completed it once onboard a road bike (I
usually use a 26/34 or 26/26 on my mountain bike and have gone over
backwards on this climb) so I was trying not to slow too much and in
hindsite had too much speed in view of the curb transition.


--
meb