Tire Pressures?

[LakeWylieJoe_imp]

FBI Agent...

The way we measure tire pressure is called gauge pressure; it's the difference between the pressure in the tires and the ambient (outside) air pressure. If the amount of air molecules were fixed (no leaks), the gauge pressure varies with altitude, temperature, barometric changes, etc.

A quick example. If you pump your front tire up to a reading of 36psi at sea level at standard temp and barometric pressure, then take it to the moon, the reading there will be 36psi + 14.7psi (50.7psi) because there isn't any ambient pressure pressing back on the outer surface of the tire. There was 14.7psi pushing on the outside of the tire at sea level. And yes, the tire will be hard as a rock on the moon with that amount of air in it and wouldn't have a proper contact patch even if the gravity there put the proper amount of weight on the tire. Also, a flat tire at sea level will magically have 14.7psi in it in space, assuming it doesn't leak...

All that being said, the 36 & 42 psi pressures are a good compromise for a given load within the CB1100 carrying capacity specs at any temp, barometric pressure, altitude, etc. as long as you properly set the pressures before riding. I'm sure there is a perfect pressure for each load on the bike, but figuring all that out and constantly monitoring and adjusting the pressure as the temperature changes during the day isn't practical.

A tire with a gauge pressure of 36psi in Qatar will have less air in it than a tire with a gauge pressure of 36psi in Iceland on the same day. This is a good thing. Both give a good contact patch and wear characteristics and that's why we go with a fixed gauge pressure wherever you happen to be.

I used to be a physicist. :-\

Thanks Joe. Um, what are you now?

Thanks Joe. Um, what are you now?