Just a quick note - I have read that the tire pressure(s) on tire sidewalls do not represent optimum pressures, rather, they represent the manufacturer's attempt to limit their legal liability. The high pressure stamped on the sidewall is a fraction (maybe about 1/2) of the PSI that will cause the tire to blow off a typical rim. If there is a second lower pressure on the sidewall, it represents a multiple of the PSI that will cause the tire to roll off a typical rim. Neither pressure on the tire's sidewall is optimal ...optimal PSI depends on the actual load on the tire. Check out http://www.michelinbicycletire.com/m...rpressure.view and also http://www.bikequarterly.com/images/TireDrop.pdf )