Mountain bikes have lower recommended tire pressures than road bikes, with 25 to 45 pounds per square inch, or psi, common on mountain bikes, compared with 65 to 130 psi on road or commuter bikes. Within the range of mountain bike tires, clincher tires with separate inner tubes use higher pressures than tubular tires, which include the inner tube and are glued to the wheel rims.
Sizes
Mountain bike tire widths range from 1 inch to 3 inches, with widths less than 2 inches generally used for street or a combination of street and simple hardpack trails. The thicker, wider and heavier a tire, the less air pressure it needs. Wide mountain bike tires, more than 2.125 inches, are optimal for complex terrain requiring a lot of traction, and the low tire pressure helps them maintain traction. Generally, the narrower the tire, the less knobby the tread, and the less suitable it is for environments where you need a lot of traction.
Performance
When tire pressure is too high, the bike bounces off obstacles rather than gripping them and turns corners poorly. When the pressure is too low, the inner tube may get more pinch flats, in which the tube is caught between the tire and the rim. Pedaling will not transfer energy to the bike's momentum as efficiently. If you're riding in sandy conditions, lowering the tire pressure increases the contact area of the tire on the ground, providing more traction. On muddy terrain, increase the tire pressure so the wheel cuts through the mud more firmly.
Speed
If you ride your mountain bike primarily off-road, you'll want to use a lower tire pressure than if you use your mountain bike mostly for road riding. High pressures cause less rolling resistance, which is the pressure caused by the wheel deforming and reforming as it hits the road. But in off-road conditions, you generally want greater traction, which you can get by using low pressures.
Solution
To avoid damage and get optimal performance, inflate your tires to the upper end of the recommended range printed on the tire if you ride on paved roads or simple terrain. Inflate the tires toward the lower end of the range if you ride complex and rough terrain. The Bike 198 website recommends running 26 to 28 psi on tubeless tires and 28 to 32 psi on clinchers for a rider weighing 190 lbs. Lighter riders may be able to use lower pressures, and heavier riders higher pressures. Generally, inflate tubeless tires 5 to 7 psi less than the same size clinchers meant for equivalent terrain. To maintain the recommended tire pressure, check it at least once a week and reinflate as necessary.
Expert Insight
According to Pete Prebus of MountainBikeRiding.com, you can find your optimal tire pressure by inflating the tires to about 45 psi or the highest recommended pressure printed on your tire. Ride on one section of terrain and decrease or increase the pressure by about 5 psi at a time, retrying the course each time until you find the best pressure.
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