if the road surface is PERFECTLY smooth (like an absolutely flawless velodrome) then it is not too high.

however, on real, varied roads it is exceedingly difficult to say for certain what the exact optimal pressure is for given conditions and varibles, as there an astounding no. of them that must be considered.

so is that useful advice? probably not...

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Where would you want to swim ?

140 for clinchers is too high and borderline dangerous. If you have any serious descending to do, hard braking could heat up the rims and increase tire pressure beyond the limits of the rim to hold the tire. Studies have shown that much over 120 is overkill and on harsh surfaces can even slow you down.

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Cousin Elwood - Team Over-the-hill Racing
Brought to you by the good folks at Metamucil and Geritol...

I think Elwood is about right there.

I saw on here somewhere a calc that started off at 115psi and you added lbs and took it off for various factors, weight, heat etc.

Certainly I've blown my 140psi tyre out on a long alpine descent - heavy traffic so I was braking way more than normal, but it could have been nasty.

"Certainly I've blown my 140psi tyre out on a long alpine descent - heavy traffic so I was braking way more than normal"

Surprisingly, you can increase rim temps to greater than 300º under conditions like that, at which point you've added more than 20psi to the cold inflation pressure (approx 1psi/10º). So if you started at 125psi in your 60º garage and braked hard down a windy 10-15% descent, you could be over 150psi by the time you get to the bottom.

Another good reason NOT to drag your brakes!

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Cousin Elwood - Team Over-the-hill Racing
Brought to you by the good folks at Metamucil and Geritol...

One of the tire companies has a great set of these calculations; does anybody know who it is? The reference was posted here about six months ago, but it has completely slipped my mind. Help?

The figures I was thinking of are at www.nimble.net. There are options on the right, one of them is Tire Pressure Instructions.

conti gp 3000's have a max pressure of 160 psi for the 700x20...the super sonic gp is even rated higher. i use the gator skins for training, live in a very hilling area, i pump mine up to 130/140 and have no probs at all.....but i dont use my brakes going down hill...what fun is that!!!

one thing that should be considered, thr wheel/rim might have a psi rating........

This is a valuable resource:

http://www.cyclingnews.com/...atures/conti_factory

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Tom Demerly
The Tri Shop.com

GP 3000 23s indicate a max pressure of 120.

I question the efficacy of 20 or 21mm tires for training. I bought several sets of Specialized 21s a few years ago, because they were priced so well, but then they just wore out a lot faster. I also tried a tire that was rated for 150 psi. Nowadays I use a 23 front (GP3000) and 25 rear (GP 4 seasons) and find I can get close to 2000 miles on the rear and over 3000 on the front.

Bottom line is that pressures above 120 only slightly reduce rolling resistance (if at all) and only if the pavement is very smooth. With clinchers, there is the problem that even if the tire can withstand 160 psi, very few rims are designed to handle that, afik. I'll deal with suicidal squirrels, migrating tarantulas and all the other road hazards out there. I just don't EVER want to lose a front tire on a winding descent!! I know guys who have, and it ain't pretty.

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Cousin Elwood - Team Over-the-hill Racing
Brought to you by the good folks at Metamucil and Geritol...

I always inflate to what the manufactuer suggests as the max pressure. On my clichers - 140 psi. I haven't had any problems, ever. As for my tubulars I inflate to 210 psi. In fact I called the manufactuer of my tubulars and asked if I "should really" inflate to 210. His accented response was, "why would you want to ride on a flat tire, these tires are rated for 210 psi and should be ridden at that pressure".

That is akin to asking your car dealer about something as well. Try calling Michelin or Continental (dedicated tire manufacturers) and ask the same question. My guess is you tried Vittoria or Tufo - although customer service reps certainly aren't tire engineers. I grew up in Akron, OH and have loads of family/friends who are "tire" engineers. Amazing the amount of technology that goes into tires (even though bike tires are pretty straightforward, especially clinchers).

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Fatigue is biochemical, not biomechanical.
- Andrew Coggan, PhD

The blow out pressure of all these tires is 2 times the listed max. per UL.

Idiot.

210 is for the track. Just because a tire can stand the pressure doesn't mean it's fast like that.

If a pickup is rated to carry a max load of 3/4 ton, does that mean you should drive it all the time with 3/4 ton of sand loaded in the back?