Originally Posted by
Dan The Man
For road bikers it is almost always more efficient to have higher pressure tires. The only thing holding them back is the max pressure rating of the tires. Therefore, tires get pumped up to their maximum rating.
Actually the limiter on pressure is handling considerations. More pressure does lower rolling resistance, but after a point the improvement tapers off. Meanwhile more pressure makes tires more skittish (for lack or a more precise word) and causes them to bounce off small bumps rather than absorbing them through deflection. That decreases the connection to the pavement and lowers traction. Ideal pressure depends on conditions and reflects a balance between these conflicting goals.
Counter-intuitively there's good dyno data available showing that wider tires at lower pressure actually have lower rolling resistance than narrower tires at higher pressure. But don't run out and get fat tires right away. Fatter tires weigh more and create higher air drag.
Peak performance is obtained with the best balance of tire selection and inflation pressure for road conditions, and not simply highest pressure.