Every tire has a sweet spot where it rolls faster and yet absorbs road shock—and more pressure is not always better, as many believe. Three features determine where this mythical tire pressure should be set. First, check the ratings on the tire. Some are rated as high as 220psi and others as low as 125psi—usually there is a high/low range, and the best place to begin is the middle.
Second is the diameter of the tire. Smaller-diameter tires (19mm) require significantly more pressure to support the same weight when compared with a larger-volume tire. One hundred psi may be more than ample for a 25mm casing while a 19mm TT tire will run almost flat at that pressure.
Third is rider weight. All you need is sufficient air pressure to prevent unnecessary tire flex, and not so much that you bounce all over the road on rough pavement. Riders in the 200-pound range will discover that they can get a smooth, efficient ride at close to the tire's maximum rated pressure, while a 105-pound female or junior rider may achieve the same performance near the tire's minimum pressure rating.
Any time your bicycle bounces, you are trading horizontal momentum for upward acceleration that is never recovered. What makes a pneumatic tire efficient is that it deflects over objects it contacts without lifting the mass above it (you and your bike), and as it rolls over the object, it springs back and returns most of the energy it stored as it rolls over the back side of the object.
This happen billions of times in a day's ride, so if you use the correct tire pressure, you can save gobs of energy in the form of better rolling resistance. Too much pressure will rob your strength—especially if you are a lightweight rider. If your bicycle bounces, release five or 10 ounces.