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Old 06-14-05, 04:57 PM   #1
TheRCF
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Pinch flats

I need to get some views of others here to see if I have the wrong idea about pinch flats.

I do get more than my fair share of flats and, as I guess is usual, some I can't find the cause.

Well, today another rider I know said he was driving on a road I use and said he wasn't surprised that I get so many flats. When I asked him why, he said because the road is so bumpy, causing pinch flats.

Well, the road overall isn't so bad, but it does have some spots you can't avoid consisting of patched holes that will bounce you a little when you hit them. But it isn't like dropping into a pothole or anything. I always considered this to be pretty normal stuff for bike riders.

Anyway, I figured that since I keep my tires up to 120 lbs, I wouldn't get a pinch flat from hitting these little bumps, but am I wrong?

Statistics: Total weight of bike, me, and everythnig I carry in my backpack - approximately 200 lbs. Speed when hitting these patches probably doesn't exceed 15-16 mph on a good day.

Bob
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Old 06-14-05, 04:59 PM   #2
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how big are your tires? Are you using the proper size tube?
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Old 06-14-05, 05:10 PM   #3
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Tire are 700x23. I have various tubes, but all are in the proper range according to the boxes.
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Old 06-14-05, 05:16 PM   #4
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A pinch flat has a very distinctive signature: Two holes side by side, like this :
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Old 06-14-05, 05:25 PM   #5
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At your size (and mine...) you do have to be careful of those sharp edges. Potholes, steel construction covers, that sort of thing.

If your streets are an obstacle course, you might try heavier tubes and/or reinforced tires.
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Old 06-14-05, 05:57 PM   #6
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What tire pressure? Do you check pressures daily/every ride, or wait 'til they feel soft before you top off?
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Old 06-14-05, 07:48 PM   #7
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Quote:
Originally Posted by JavaMan
A pinch flat has a very distinctive signature: Two holes side by side, like this :
No, I don't have "snake bite" punctures - but I wasn't sure whether or not a pinch flat ALWAYS resulted in that.
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Old 06-14-05, 07:50 PM   #8
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Quote:
Originally Posted by Bikewer
At your size (and mine...) you do have to be careful of those sharp edges. Potholes, steel construction covers, that sort of thing.

If your streets are an obstacle course, you might try heavier tubes and/or reinforced tires.
I'm not dealing with sharp edges, just patchwork on the roads that will make for some bumping. There is a place they recently put in those big steel covers, but they all have blacktop around them, eliminating the sharp points.
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Old 06-14-05, 07:53 PM   #9
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Quote:
Originally Posted by BostonFixed
What tire pressure? Do you check pressures daily/every ride, or wait 'til they feel soft before you top off?
Pressure is 120 lbs. I don't always check EVERY ride, but usually top it off, ride, rest a day, ride again, and then top it off again before the next ride.

I have found that generally when I top it off the next time, the pressure is still close to 115.

I do feel them, just in case a small leak was working against me, but that's all. I know that the "feel" approach isn't all that reliable beyond catching a flat coming on early.
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Old 06-15-05, 04:59 AM   #10
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Quote:
Originally Posted by TheRCF
I do get more than my fair share of flats and, as I guess is usual, some I can't find the cause....Anyway, I figured that since I keep my tires up to 120 lbs, I wouldn't get a pinch flat from hitting these little bumps, but am I wrong?
Curious: What pressure are your tires rated for? Assuming you align the tire label with the valve hole, when you can't find the cause of the flat, do you submerge the tube to find the leak, then look to the corresponding spot on the tire for the source?
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Old 06-15-05, 12:01 PM   #11
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Strange, I know I've seen the figures for the pressure, but looking at the tires just now, I can't find it. Maybe the pressure was on the box, but I thought all tires had them labeled on the tire itself. Anyway, it was either 120 or 125.

As for finding leaks, if I don't see the problem right away, I do pump up the tube to see where it is leaking and then line it up with the tire so I can search that area more carefully and sometimes I have to use water to find really slow leaks.

Of course, sometimes the cause of a flat simply falls out or something so you never know. I simply hope to find out whether or not a pinch flat is possible even with tires pumped up to 120 lbs if the only impacts the tire receives are from road patches (not pot holes, etc, that have sharp edges).
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Old 06-15-05, 12:08 PM   #12
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Quote:
Originally Posted by TheRCF
No, I don't have "snake bite" punctures - but I wasn't sure whether or not a pinch flat ALWAYS resulted in that.
Are the holes in the tread side of wheel side of the tube?

Are you sure it's not a sharp edge on the rim or dodgy rim tape?

What brand/model of tire? Might just not be very resilient...
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Old 06-15-05, 12:23 PM   #13
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The holes are on the tread side. The present wheels don't use rim tape and I can't find sharp edges either, but like I said, the holes are on the tread side anyway.

The guy was referring to my general record of flats over several years and I've used various tires (Hutchinson Carbon Comps, Conti 4-season, Conti GP 3000).

I liked the carbon comps - light and fast - but they had two problems. One was the soft rubber cut easily. But I could get them at a good price so replacement wasn't a big deal. However, I also found that when they did get damaged from glass or something, that apparently they were far more likely to cause more flats from the damage, apparently, than other tires I've used. But the conti tires I've gone back too cost so much more!
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Old 06-15-05, 12:25 PM   #14
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If I may repeat my basic question - is a pinch flat possible or probably just from riding over some road patches (no sharp edges - just a bump) if the tire is inflated to 120 lbs?
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Old 06-15-05, 12:29 PM   #15
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Quote:
Originally Posted by TheRCF
If I may repeat my basic question - is a pinch flat possible or probably just from riding over some road patches (no sharp edges - just a bump) if the tire is inflated to 120 lbs?
Possible, yes. Probable, no.

In any case, your flats don't sound like pinch flats.
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Old 06-15-05, 02:13 PM   #16
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Quote:
Originally Posted by TheRCF
If I may repeat my basic question - is a pinch flat possible or probably just from riding over some road patches (no sharp edges - just a bump) if the tire is inflated to 120 lbs?
It's not likely that road patches would cause pinch flats, even if you ran 100 psi in your tires.

I don't get pinch flats often, but when I do, it's from running over small rocks in the road.
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Old 06-15-05, 02:49 PM   #17
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Quote:
Originally Posted by TheRCF
I simply hope to find out whether or not a pinch flat is possible even with tires pumped up to 120 lbs if the only impacts the tire receives are from road patches (not pot holes, etc, that have sharp edges).
I just re-read Jobst Brandt's article on snakebite (pinch) flats.

Based on that analysis, it would appear that is possible but not probable that you're getting a series of pinch flats from that road. Something would need to be causing the rim to bottom out, and the small bumps you've described wouldn't seem enough.

Also, you said you weren't seeing the snakebite pattern. If it's pinholes you're finding, it's probably not pinch flats. Around here, I get holes from these stubby thorns that live in the grass. They are tough and long enough to puncture, but they fall out. Maybe it's something like that. Try cutting an old tube in half and using it as a tire liner.
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