Tire PSI: Sidewall vs Chart
 

My Trek 7.1FX has Bontrager H2 700x35 tires, and the sidwall says to inflate to 60-80psi. On the Bontrager website they have a pressure chart for all of their tires and the chart lists the H2 700x35 as 60-95psi. Which one is right? I would sure like to try 95psi, is there any reason I shouldn't?

I wouldn't exceed what the sidewall says.
But if there is a failure, I would expect the rim to fail before the tire did.

It'll give you a harsher ride and probably at best an insignificant decrease in rolling resistance. But there shouldn't be any problem with trying it out. With current hooked-edge rims tires should have a large safety margin when inflated to the rated pressure so going over a little (if it is even over at all in this case) shouldn't cause a problem as long as it doesn't exceed the rim's capability.

Is this a serious statement????

I have never blown a tire from excess pressure.
I have *twice* broken rims from excess pressure, (which was within what the sidewall stated).
70psi on a 2" tire.
At a constant pressure, force on the rim increases as tire size increases.

You can't go wrong if you use the manufacturer's suggested tire pressure range that's embossed on the tire itself. Charts can be and often are incorrect. It may just be information that's not up to date, or mixed up with other tire sizes/widths. It just depends on who put the chart together and if it's been updated if possible changes in the structure of the tire have been made in the manufacturing process. The manufacturer would have a problem disputing a manufacturing defect if the tire pressure indicated on the tire was followed. After you get to know your tubes, you'll know exactly how much air you'll lose during a given time period. I know my tubes will hold at just above the maximum recommended pressure for several days, and after a week to ten days the tubes will be down ten pounds total pressure to five pounds under the recommended pressure. So I know after a week of riding I should air up again for my tubes to be at a safe pressure for riding conditions. Nearly every instruction you'll see about changing/repairing a flat tire will always tell you to follow the air pressure recommendation on the side of the tire.

Why in the world would you want to go that high on 35mm tires? There's no advantage whatsoever and you'd end up with a much harsher ride.

I run my 700x35's at 65psi when I'm riding my loaded touring bike, and that's just about ideal.

I do not recommend exceeding the maximum pressure listed on the sidewall. Tire blowout/rim failure is a possibility. If you're needing to put that much air in your tire you should get a wider tire and run it at an appropriate pressure.

+1000 95psi in a 35mm tire would be way too much for me but I'm also a lightweight. I run my 35mm tires around 50-60psi. Putting more air in doesn't make you go faster, it just gives you a harsher ride. The only thing you need to worry about at the low end of the pressure range is bottoming out the tire and getting a pinch flat/dented rim. If you're running a really low pressure you'll also be slower on pavement (duh.)

So at 80psi my tires are as efficient as they're going to get? The reason I wanted to try is because I don't have experience with much of this and wanted to experiment and learn what works. But if this isn't going to help then I won't try it.

Unless you're really heavy, even 80psi is far higher than most people would use on 35mm. The larger the tire, the lower the pressure you'll want to use. On my Pelican with 42mm tires, for example, I run 45-50 in the rear and 40-45 in the front, depending on whether I'm on pavement or dirt/gravel.

Have we reached a new level of maturity?

So far nobody has mentioned the thing about blow off pressure being double the pressure marked on the tire's sidewall.

You can find tons of graphs of tire psi vs rolling resistance. You might reduce the rolling resistance by ~5%, at the expense of significantly worse handling.

I'm definitely in the clyde club at 255. At 80psi even the substantial gaps in the asphalt aren't all that rough as long as I see them coming and pick my butt up. I read a lot of statements about bigger tires being even more efficient than skinny tires when run at higher pressure, but they're never rated for high pressures like skinny tires. But the consensus here is unanimous that there's no reason to go higher than 80psi, so there I shall remain.

And even that's highly dependent on the surface. The rougher the surface, the less an increase in pressure is going to reduce rolling resistance. Raising pressure can even increase rolling resistance because the tire has to bounce over things instead of being able to just roll over them - and bouncing redirects motion and absorbs energy.

Why would a large tire at high pressure literally blow a rim apart? Let's see: 2" tire at 100 psi. Assume a 1" radius for the inflated tube cross section, and a 13" radius for the tube itself. Surface area of a torus is:

4 x pi^2 x R x r

4 x 3.14^2 x 13 x 1 = 513 square inches

At 100 psi, the outward pressure on the tube totals over 51,000 pounds.

Yea, but more likely to increase rolling resistance with too much pressure. The tire can't conform as well to the road surface and will bump over roughness rather than rolling over it. The idea of increasing pressure = decreasing rolling resistance assumes a smooth surface, not a normal road.