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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 01-27-07, 11:23 AM   #1
kcorwin
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Air pressure in cold weather?

I just got a pinch flat from going over what seemed to me to be a pretty small pothole. (Actually it was one of those ruts they dig in the road when they're doing road repair crap, but whatever.) Was about 30 degrees out, and I had *just* pumped up my tires to their recommended 120 psi about 10 minutes before I left. 700x23c, if that makes a difference, running Gatorskins. I've certainly hit potholes harder in the past, and I never got a pinch flat before.

Now, my bike lives in my apartment, so presumably when I went out in the cold, it caused the air pressure in the tires to drop. Not sure if this was the cause, but... anyone compensate by inflating their tires extra in the cold? Or is that a bad idea? Are pinch flats an inevitable part of riding (relatively) high-pressure tires in the cold, or is this all a crazy coincidence?
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Old 01-27-07, 12:20 PM   #2
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Im told that the narrow range of temps that humans can tolerate doesn't make much of a difference to air volume. I think it prolly wouldn't be sufficient to drop a 120 psi 700*23 tire down into the pinch flat zone. Maybe someone else knows different though.
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Old 01-27-07, 12:31 PM   #3
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120psi is a bit much.
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Old 01-27-07, 12:31 PM   #4
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Temperature can effect tire pressure, but not by very much.
You probably had a slow leak and by the time you hit the p-hole most of the air had already leaked out.
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Old 01-27-07, 12:37 PM   #5
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Quote:
Originally Posted by na975
120psi is a bit much.
It is? But aren't pinch flats caused by under-inflation, not over-inflation?

Regardless... out of curiosity, what PSI do you run on the street?
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Old 01-27-07, 12:45 PM   #6
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i ride bout 110
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Old 01-27-07, 12:55 PM   #7
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Old 01-27-07, 01:41 PM   #8
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i ride 110 in the back and 100 in the front
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Old 01-27-07, 02:02 PM   #9
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I don't know about pressure changes, but can't the cold (sub-zero) back the inner tube rubber more brittle? Does anybody know the operating limits of Halobutyl rubber?
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Old 01-27-07, 02:29 PM   #10
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Coincidence. You got a pinch flat, don't read too much into it. You seem to already know what to do with tire pressure.
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Old 01-27-07, 04:57 PM   #11
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Thanks for the help, all. Considering I run a higher PSI than some folk around here, it seems like doing it up any more will be a bad idea. Also sounds like the PSI isn't dipping as much as I think anyway.

The brittleness of the rubber in colder temperatures is an interesting thought. If this happens again, I'll try getting better inner tubes. But since this is the first time it's happened, I'm willing to call it a coincidence for now.
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Old 01-27-07, 05:45 PM   #12
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I've been running 120psi for a long time and have never had problems with it being too high.
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Old 01-27-07, 06:15 PM   #13
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Quote:
Originally Posted by na975
120psi is a bit much.
Unless of course it's the recommended pressure.
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Old 01-27-07, 06:19 PM   #14
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120 is too much? I like mine at 135psi.
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Old 01-27-07, 06:49 PM   #15
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What pressure is a "bit much" would depend on what your rims and tires can handle.

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Old 01-27-07, 06:49 PM   #16
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erm 120 is perfectly fine. for most adults 110 is actually a touch soft. sounds like just an unfortunate incident to me. i wouldn't read too much into it, and i certainly wouldn't see the need to increase your tire pressure unless you wanted to change your ride quality.
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Old 01-27-07, 11:09 PM   #17
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I ride 120-125 on the street, but I'm a colossal, hulking ******.
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Old 01-27-07, 11:14 PM   #18
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Those ruts they dig to do construction aren't usually the smoothest cut in pavement. you probably hit a pretty gnarly edge and it got you just right. pinch flats happen sometimes, regardless of pressure, some of them just can't be avoided depending on the object.
example: really hard curbs with sharp angles.
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Old 01-28-07, 06:50 PM   #19
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I heard about this one kid, on a really cold day, in maine, who pumped up his tires outside (fixing a flat) and when he brought his bike inside, his tires exploded and killed his dog. (the dog really loved him and came to greet him everytime he came home)

or maybe I just made that up.
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Old 01-28-07, 07:27 PM   #20
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Quote:
Originally Posted by operator
Coincidence. You got a pinch flat, don't read too much into it. You seem to already know what to do with tire pressure.

What he said.
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Old 01-28-07, 07:42 PM   #21
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Going for ~70 F to ~30F would drop your tire pressure about 10 PSI, according to Gay-Lussac.
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Old 01-28-07, 08:18 PM   #22
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I ride on 130psi tires and inside they will be 125 outside feels like 110 but it isn't a huge difference 70 ish inside and 30ish outside
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Old 01-28-07, 08:28 PM   #23
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Quote:
Originally Posted by zacked
Going for ~70 F to ~30F would drop your tire pressure about 10 PSI, according to Gay-Lussac.
Yes.

T1 = 70F = ~530R
T2 = 30F = ~490R
P1 = 120psi

P1/P2 = T1/T2
P2 = T2/T1*P1
P2 = (490/530) * 120psi = ~111psi


In other words, a 40 degree drop in temperature won't make a damn bit of difference.
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Old 01-29-07, 01:18 AM   #24
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I doubt 120 psi is too much. When in doubt, read your tires. I run Conti gatorskins at 120 on my fixed gear, and some Vittoria Diamante Pros on my geared bike at 130 (up to 150 if I'm just riding on real smooth pavement).
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Old 01-29-07, 02:29 AM   #25
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100psi for 28mm Conti Gatorskins. 120psi doesn't sound out of line for 23mm at all.

Edit: yeah, Continental's own site lists 120 for 23mm. If your rims can handle it, you're fine.
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