Tire Pressure

I believe my tires say max 120, but the bike shop sez 115 is the max. That's where I pump them to before every ride. Yes, they are very hard, and they are made for that. I've never had any problems. Good luck to you.

First a whole bunch of questions...

What is your tire/rim combination?
What condition are your rims in?
What about the tires?
How are you measuring the pressure?
What was the pressure when the tires popped?
Are you *sure* the tire bead was correctly seated?

Most tires, when mounted on appropriate rims can handle a good
deal of overinflation before the bead comes loose. If the tire is rated
at 120 psi, for example, 140 will still be safe.

Road bike tires should feel really hard, but your should be inflating by a pressure guage, not by feel.

Edited by ride_like_u_stole_it 2004-06-02 11:52 AM

I accidently started a new thread with my reply - hit the wrong button! Anyway, what I was trying to say here was that a friend of mine who is a criterium racer as well as an experienced tri'r had given me advice that during normal riding coniditions that 100 - 110 psi was ok. It was not necessary to inflate to 120 psi or more.

Now at the time of the psi conversation we were on a week long pleasure ride and not talking about a competitive racing situation. I'll have to clarify that with him and ask if that's what he does during races. I normally ride 100 - 105 psi w/o any issues.

I've had a buddy pop one on my bike, a bike mechanic and just this past weekend I popped one. I can't figure out what it is. The two guys both had pressure gages and were using a floor pump, I was using CO2 with no gauge. I haven't had my bike for very long so my tires and rims are both in good shape. In fact, after my first blowout I got two new tires. Now I put a thicker tire on my back wheel because that's always the one that seems to have the problems (still have my original tube on my front tire). When I had my most recent blowout, I scratched up the back rim so I'll get that sanded down before I go on another ride. Does weight have anything to do with it? I'm about 6'1" 175 so maybe I need a thicker tube cuz I'm heavier?

Is it just harder to ride on a low tire or does it do damage to the rim??

Riding on a low tire increases the likelihood that you may end up "creeping" the tube around the rim slighty, causing damage to the valve stem area. Less likely with the metal presta valve stems, but you should inflate the tires to the recommended pressure. In 30 years of bike riding and racing, I've never popped a tube during inflation. If that's happening, there could be a number of reasons:

1. The tube may have been defective or had a weak spot in it.
2. The tube may not be properly installed, may be slightly twisted or pinched during inflation. During installation, put a slight amount of air in the tube, just enough to barely give it some shape, then insert it in the tire. After the tire beads are over the rim edges. Once the tire is on, push up against the valve stem slightly with your finger, to ensure that the edge of the stem is not being pinched in the rim hole. Pump up the tire to 30 PSI or so. Check the edges of the tire and see that the tell-tale line on the rubber is equidistant around the circumference of the rim. This will insure that the bead of the tire (usually made of either metal or Kevlar) is correctly positioned. If all looks good, inflate the tire to the pressure on the sidewall. The tube under full pressure will conform to the tire inner surface. Nothing should "pop" the tube unless it is a rim or tire defect.
3. Make sure you are using a rim strip so that the spoke ends are not poking the tube. Sometimes these ends need to be filed down so that they don't protrude past the inner nipple surface.
4. Check the rim for sharp edges and burrs that might puncture the tube. If you are repairing a flat, you should try to locate the cause of the flat. It could be a thorn or tiny piece of metal. I once picked up a small piece of wire from a wire brush that was in the tire. If you don't get it out, chances are it will simply be the cause of Flat Tire #2

Tires can withstand more pressure than their specified rating. For liability purposes, tire manufacturers routinely test their tires at least 1-1/2 times the sidewall pressure, just as a safety factor. Of course they don't want you to know that, otherwise people would be pumping up tires to outrageous pressures. But if it says 120 PSI on the tire, it's very safe to go to that pressure. Harder pressures will give a less shock absorbent ride, but will have less rolling resistance and be slightly faster. Olympic track riders routinely pump up their tires to around 200 PSI, since the difference between winning a medal and losing can be thousandths of a second.

Max

First, there is some variation in the proper inflation pressure for road tires,
usually in the range of 100-150 psi for clinchers,
and up to 180-200 for Tufos or true tubulars.

The lower a pressure you run, and the heavier you are,
the greater your chance of pinch flats. I too am a big(ish) guy
and I always run my tires at or a *few* pounds above the max rated pressure
I have never had one blow off in 20 years of road biking, or a pinch flat either.
And, yes, a tire below the reccomended pressure can increase rolling resistance
and make for a higher than necessary energy expenditure, and a lower than possible speed

That said, no 700c tire rated for 120psi
should blow off the rim at the reccomended pressure,
something is wrong.
I suspect there is a problem with your rim,
I would suggest cleaning the bead of the rim (with the tire removed) carefully
with some alcohol to see if you have some sort of contaminant (grease, stray chain lube)
on it and inspect it carefully to make sure there's no defect

Thanks for the suggestions guys! Can't wait to play around with my tire when I get home tonight and see what I can do to stop the confounded tube problem.