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PSI as a means for flat protection.

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PSI as a means for flat protection.

Old 04-02-11, 01:19 PM
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HMF
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PSI as a means for flat protection.

I tend to run my tires in the "cushy" range- 700x25c @ 85psi for my rear tire. While out riding today, I got a flat after I ran over some glass. I was close to home so I wasn't too worried about getting the tire all the way back to full inflation, so I probably got it up to about 50psi. A few miles later I got another flat (in a different location, so no, it wasn't the glass still in the tire) from an unknown object.

That sort of got me wondering. Does tire pressure have any effect on your chances of flatting? Would a tire at the highest recommended pressure have a better chance at deflecting objects?
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Old 04-02-11, 01:29 PM
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Lower pressure increases the likelihood of a pinch flat.
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Old 04-02-11, 01:33 PM
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High pressure. If you want a more cushy ride, get thicker padding on your shorts.
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Old 04-02-11, 02:23 PM
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I used to get constant pinch flats on road tires because I would always forget to keep them pumped up. I switched to a wider tire to fix the problem instead of fixing my absent mindedness.
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Old 04-02-11, 03:22 PM
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so basically no research to support my original question regarding debris. k
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Old 04-02-11, 03:23 PM
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Originally Posted by dennisa View Post
Lower pressure increases the likelihood of a pinch flat.
And higher pressure increases the likelihood of a puncture.

There's a happy medium, but it really depends on the size of the tire and rider weight. And sometimes the flat tire gods just have it in for you and there isn't much you can do about it.
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Old 04-02-11, 03:25 PM
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125psi on front and rear. 8000 miles without a flat on the bike. Two flats happened overnight.
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Old 04-02-11, 04:15 PM
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i ride on michelin pro 3's in a 700x23 a ride them at max pressure 115. i have used them as a winter tyre so have been road in salt roads, wet roads and during the summer aswell, and i never got a flat in 2500 miles, until yesterday. so i need to replace them now, so i feel the higher you can go to the max pressure of the tyre the better
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Old 04-02-11, 04:21 PM
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Originally Posted by Brian Ratliff View Post
And higher pressure increases the likelihood of a puncture.
Think of a balloon. If you blow it up to the max, you can easily puncture it with a needle; but if you inflate it half way, it'll flex when you push against it with that same needle.

As Brian R posted, you have to work out the correct combo for you - which I think you've already done.
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Old 04-02-11, 04:31 PM
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we seem to have conflicting anecdotes here.
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Old 04-02-11, 06:55 PM
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Originally Posted by HMF View Post
we seem to have conflicting anecdotes here.
Not really. It's pretty simple both as a mtter of physics and experience.

Higehr pressure, ceterus paribus, decreases the risk of pinch flatting.

Higher pressure also increases the risk of punctures.

There's not a confict there, just a trade off.

What is true in both circumstances is that being attentive to road hazards decreases the risk of punctures and pinch flats.
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Old 04-02-11, 07:12 PM
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Originally Posted by merlinextraligh View Post
...
What is true in both circumstances is that being attentive to road hazards decreases the risk of punctures and pinch flats.
This needs to be emphasized. People who are "flat prone" are usually not so much flat prone as "run over crap" prone.
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Old 04-02-11, 07:21 PM
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Originally Posted by HMF View Post
we seem to have conflicting anecdotes here.
you just have to understand the diffrence between a pinch flat (curb/pothole + rim => pinched tube) and a puncture (glass/nail/pointy thing penetrates tire). pressures that are more protective for one make you more susceptible to the other.
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Old 04-03-11, 07:57 AM
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Originally Posted by FogVilleLad View Post
Think of a balloon. If you blow it up to the max, you can easily puncture it with a needle; but if you inflate it half way, it'll flex when you push against it with that same needle.

As Brian R posted, you have to work out the correct combo for you - which I think you've already done.
Even if your analogy is accurate, which I suspect is too simplistic to be the case, inflating tires to half the required pressure will almost guarantee a pinch flat on all but the smoothest surfaces. OTOH, with modern tires flats, are pretty rare on a per ride basis.

IOW, even if there is a low pressure flat to high pressure flat correlation, it is probably not one to one. Likely closer 1:100.
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Old 04-03-11, 10:56 PM
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roger, you're over analyzing.

Last edited by kevrider; 04-03-11 at 11:00 PM.
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Old 04-03-11, 11:06 PM
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Go higher pressure, for sure. 100-120 psi is the norm, and is an excellent pressure for roadie riding.

Pinch flats come up at an alarming rate at <80 psi. Punctures for me are fairly infrequent even with cheaper tires.
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Old 04-03-11, 11:10 PM
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Originally Posted by Brian Ratliff View Post
This needs to be emphasized. People who are "flat prone" are usually not so much flat prone as "run over crap" prone.
This. Dont ride on the shoulder if there is debris.
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Old 04-03-11, 11:26 PM
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Originally Posted by FogVilleLad View Post
Think of a balloon. If you blow it up to the max, you can easily puncture it with a needle; but if you inflate it half way, it'll flex when you push against it with that same needle.
OTOH, a tire inflated to a higher pressure will have a narrower contact patch and therefore is less likely to contact the 'needle' at all.
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Old 04-04-11, 06:20 AM
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Originally Posted by kevrider View Post
roger, you're over analyzing.
You're just projecting

Me? I'm just using some common sense.

Last edited by rogerstg; 04-04-11 at 06:26 AM.
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Old 04-04-11, 06:53 AM
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Originally Posted by Brian Ratliff View Post
People who are "flat prone" are usually not so much flat prone as "run over crap" prone.
Quote of the week. It's always baffled me on the number of flats some riders get. But there is the answer - they just have a penchant to run over stuff.
It's probably related to the way our brains observe and analyze the landscape/road as we ride. Some people just notice road glass or nails more than others.

Last edited by teterider; 04-04-11 at 06:56 AM.
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Old 04-04-11, 06:58 AM
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Originally Posted by Val23708 View Post
This. Dont ride on the shoulder if there is debris.
Ok cool, I'll ride on the highway then.
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Old 04-04-11, 07:04 AM
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My wife weighs 110.

She rides paper thin Grand Bois Cypres at about 50 psi.

She never, ever gets flats.

Lower pressure means fewer puncture flats, all things being equal.

We never, ever get pinch flats. But then we use sensible tires.
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Old 04-04-11, 07:25 AM
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Originally Posted by rogerstg View Post
Originally Posted by FogVilleLad View Post
Think of a balloon. If you blow it up to the max, you can easily puncture it with a needle; but if you inflate it half way, it'll flex when you push against it with that same needle.
Even if your analogy is accurate, which I suspect is too simplistic to be the case,
+1. This analogy doesn't encompass the tendency of harder tyres to eject debris. And using higher pressures allows you to use narrower tyres, which are again more likely to spit stuff out the side, if not miss it altogether.
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