A simple change in tire pressure can have a profound impact on the performance of a bike. Rolling resistance, traction, reliability and the feel of the ride can be transformed by changing the pressure by as little as ten pounds per square inch.

Road tires should be inflated to the recommended pressure on the sidewall, which minimizes rolling resistance and tire wear. If your favourite routes are rife with uneven pavement or cobblestones, or if you just can't get used to the jittery feel of a fully-inflated tire, then try ten to twenty psi lower. If you use much less pressure, you run the high risk of a flat from a bump pinching your tube. If you exceed the sidewall recommendation, your tire can separate from the rim as the wheel soaks in the heat from some heavy braking.

The rules for mountain bike tires are a much less strict. Despite the astonishingly vague pressure guidelines on fat tires, you should try a pressure near the middle of the range, about 40 psi, and try changes. A higher pressure will make your tire rock hard, and should only be used if you're too cheap to buy a real bike for road riding. For the trails, a lower pressure will feel soft and squirmy, and give you the impression of being pulled backwards by the rolling resistance. Low pressures do increase traction, but they also increase the odds of getting a flat. Low pressures also make cornering unpredictable and not fun.