Originally Posted by cyccommute

I can’t really give you a hard numbers for speed due to the complexity of the factors. However, you can see trends in the chart here. In all cases in that chart, the amount of energy needed goes down as pressure go up. It’s not linear but it is significant. Look at the first entry...the Schwalbe...for example. There is more than a 35% decrease in going from 30 psi to 75psi. Less energy lost on the tires translates into a higher speed. Unfortunately, wind resistance goes up as well.

Those values are for a smooth drum. Real world data seems to show that the resistance goes up on rougher surfaces but you have to get to much higher pressures...like 120psi...to see much of effect on smooth pavement. On rougher surfaces, however, the resistance goes up significantly at lower pressures.