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?

 

[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.

 

[[email protected]]

On Tue, 5 Feb 2008 19:53:11 +1100, meb
<[email protected]> 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]

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]

On Tue, 5 Feb 2008 19:53:11 +1100, meb
<[email protected]> 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.