The first pneumatic tires were invented in 1888 by John Dunlap, a Scotsman who immediately applied the invention to the bicycle. Dunlop found that bicycle tires containing inner tubes filled with air not only provided a smoother ride but also provided a 30 percent increase in efficiency over hard rubber tires. Bicycle tires inflated with air became common by 1900. Ever since, competitive cyclists have fretted over how to determine proper tire pressure.
When putting air into your tires, it is a matter of critical importance that you never exceed the maximum pressure stamped on your tire sidewall. Over-inflated tires can fail unexpectedly with tragic results. For this discussion, your baseline pressure should start at the stated maximum and work downward.
A quality bicycle pump with a built-in pressure gauge will keep you honest. Knowing your tire maximum, your decision will always boil down to three considerations: tire width, rider weight and road surface condition.But how should you decide what pressure is best for you?
Tire Width and Compression
Most 700c road tires today are sold in either 23- or 25-millimeter widths. While these sizes tend to show up at road events, wider tires are used for cyclocross, commuting and touring. Wider tires provide a larger cross-section when in contact with the road. Because of this, they can be filled with lower pressure, resulting in a smoother ride and better control.
While some would point out that rolling resistance increases with tire width and lower pressures, there is a tradeoff. Lower rolling resistance at high pressures tends to create a harsh ride with less control. A fair amount of research has been done on rolling resistance. Generally speaking, if you maintain sufficient pressure to limit tire compression (also called 'Tire Drop') to less than 15 percent of the uncompressed vertical cross section, you will not suffer significant decreases in rolling efficiency.
To measure tire compression, place your bicycle by itself on a smooth, hard surface such as concrete or tile floor with your desired pressure in each tire. Measure the shortest distance from the bottom of the rim to the floor. This distance should measure a few centimeters in length.
Next (you'll need an assistant for this part), sit on your bicycle and place your hands on the handlebar in normal riding position. Hold yourself upright with a chair or by placing your shoulder against the wall.