Proper tire pressure is an integral part of basic bicycle maintenance knowledge. Your bike's tires are your contact with the road. Incorrect pressure can cause flat tires, blowouts or simply difficult riding. Knowing what pressure is good for your tires increases your riding efficiency and decreases flats.
Pressure Guidelines
All bicycle tires have pressure guidelines printed on the sidewall of the tire. These guidelines are usually written in several units, often containing one marked "psi," which stands for pounds per square inch and is a common unit of air pressure. These pressures are determined by several tire tests that estimate average load and riding conditions. While the standard pressure indicated is a good starting point, it doesn't necessarily represent the best pressure for your tires.
Considerations
The appropriate tire pressure depends on several factors, including the riding conditions, condition of the tire, weight of the rider and temperature. For mountain bikers who are riding on loose surfaces, a lower pressure than what is indicated on the sidewall is recommended to allow for more grip. Road bikers may increase the recommended pressure to increase efficiency over smooth surfaces. Old tires should never be inflated above the recommended pressure because they may have dry rot or cracking, which is exacerbated by excessive pressure. Heavier riders will want to increase pressure to combat the increased load. Hot temperatures naturally increase the pressure in tires, which should be considered before riding, while cold temperatures decrease tire pressure.
Tire Width
A narrow tire requires more pressure than a wide tire. When thinking of pressure as pounds per square inch, this relationship makes sense. A wider, fatter tire has more surface area to distribute its pressure while a narrow tire has less surface area. Given the same pressure, a fatter tire will exhibit more pressure on the ground because of its increased surface area. Keep this relationship in mind when switching between tire sizes as you may need to adjust your normal pressure settings.
Tips
Learn how to identify the symptoms of an improperly inflated tire by looking at the wear patterns. Excessive wear on the outside edge of the tire indicates insufficient pressure. A narrow strip of wear down the middle of the tire indicates excessive pressure. Good tire pressure shows even wear across the entire face of the tread. When you're inflating, consider that most of a rider's weight is on the back wheel, compensating by having the rear wheel at a higher pressure than the front wheel. Keep a pressure gauge and a pump with you at all times to change tire pressure as needed.
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