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Clueless about tire pressure(7 posts)

Clueless about tire pressureschills
Oct 12, 2003 1:47 PM
I run Ritchey tires on my cx bike. I'm new to this and at the last race suffered two flats from serious thorns. What is the right tire pressure? The tires have a 75psi max printed on them and I ran them close to that limit. Afterwards I was told that I was foolish for doing this, without a suggestion being offered for a more appropriate pressure. Any thoughts on what makes sense?


re: Clueless about tire pressurecross bro
Oct 13, 2003 3:44 AM
Tire pressures are very much a matter of track conditions & rider weight and it often involves making a compromise.
Low pressure - better grip - more likely to pinch puncture.
Running Ritcheys at 75psi, unless you are particularly light, and / or conditions were muddy does not sound foolish to me. In fact if track was particularly rocky would be sensible, Running those tyres at lower pressure may still not have avoided punctures from 'serious' thorns, although it may help protect from frivolous ones.
Oct 13, 2003 8:44 AM
If you're runnig over some major thorns like goat heads I don't think it will make much difference if you are running 60 psi or 75 psi.

Unless you are heavy rider (200+) , are running small tires, ride in really rocky/rooty conditions, or are a little lacking of finesse in the rough stuff, I think 75 PSI seems a bit on the high side.

I weigh about 205 and ride is some fairly rocky/rooty singletrack and tend to run about 55 psi in front and 60 psi in back. I don't have many problems with pinch flats either. I do run 700x38 tires when riding singletrack, and 700x35 for races.

If I go lower than 60 psi I will feel the rim bottom out on remounts. I guess my riding skills are more refined than my remounting skills.

Lower pressures give a much more comfortable ride, and much better traction. You just need to find that sweet spot that gives you comfort and traction but no pinch flats.
A couple more things.TWD
Oct 13, 2003 10:31 AM
To find the best tire pressure for your riding style and conditions, do a lot of experimenting. Advice over the internet will only get you in the ballpark. Be weary of anybody that gives you advice that you need to run exactly "X" psi in YOUR tires. One size fits all advice like that is worth about as much as it cost you.

My theory, is that under rougher conditions the optimum pressure is going to be the one that gives you the smoothest ride/most traction, but won't cause you to feel rim bottom out and/or pinch flat on the hardest hit that you will encouter. Until you get a good feel for this through experimentation, run a few PSI more to make sure you don't damage your rims.

If you are running 75 psi off-road now, I would recommend dropping down 5 psi to start with. If that feels good, try dropping down in 1 to 2 PSI increments each time you go out for a ride until you find a pressure that works best for you.

If you start to have pinch flats, bump your pressure back up by a couple of psi. It's best to experiment in training rather than on race day, as a flat during a race really sucks.

Once you have your pressure dialed, you will also begin to get a feel for how to adjust pressures for different courses. And conditions.

If you are on a smooth course you can get away with higher PSI if traction is good. On a smooth course with poor traction, you still want to run lower PSI since traction is more important than rolling resistance.

Conversely, on a really rough course, you may need to run higher PSI than is comfortable in order to prevent pinch flats.

Also, remember, that if you swith to different tires, you'll get different results. You'll have to experiment with those a little to dial them in as well.
re: Clueless about tire pressurelaffeaux
Oct 13, 2003 9:57 AM
As TWD said, with "serious thorns" you'll get a flat regardless of tire pressure. If you're pinch flatting, then you need more air pressure, but there's not much you can do about thorns.

I run Ritchey Speedmax 32mm tires. I've never read the side wall so I don't know what they recommend. For off-road use I run them just over 60 psi. I run the rear with a little more air then the front. I don't know the exact pressure, as my pump is marked off in 10 psi increments. I go about a needles width past 60 on the front, and a little more in the back (maybe 62 and 64 psi).

For on road use where I might ride a few dirt paths, I pump them up more. For commuting I run them above 80 psi.
Oct 13, 2003 10:10 AM
I've got tubies, so can't help specifically with your pressures, but I was running 40psi for a bit, but found that on occaision I would bottom out the tire. I bumped the pressure up to 50 the other day and haven't had any problems in the last few rides. I weigh about 180# right now, so adjust according to your weight.

From what I undersand, run just enough pressure to not pinch flat. You'll get better grip/flotation in the sloppy stuff. The higher the pressure, the less rolling resistance, but the less grip you have as well, so obviously, if its rocky run more pressure, if its soft, run less.

That help?

re: Clueless about tire pressureiml
Oct 14, 2003 3:09 PM
For 'cross and MTB, I like to go about as low as I can. Note the other posters who emphasized that one size does not fit all. That said, I can usually run 40- 50psi in either Geax Blade or Michelin Mud clinchers and have no problems in racing conditions. I'm 155lbs and a bit tall, so YMMV.