The Recommended Tire Pressure PSI for a Bicycle

by Max Roman Dilthey, Demand Media Google
Thinner tires require a higher PSI than wider tires to maintain a contact patch of a given size.


Tire pressure is crucial for safety in cars, and bicycles are no different. Since your tire is your contact point to the road, maintaining the proper pressure determines the handling and performance of the bicycle, which in turn impacts your speed and your ability to control the bike. Riding on a tire that is too flat can even cause damage to the tire and rim. Understanding how to determine the proper PSI for your tire is an important skill for any cyclist.

Bicycle Tires

The standard tire type found on most road and mountain bikes is a clincher tire. Clincher tires have two metal hoops running on the inside edge of the tire, with an open bottom that nests inside the rim. The tire is usually made from a mesh of nylon coated in rubber. The tire contacts the rim on the bead, which forms a tight seal between the rim and the outer tire. Inside of this outer tire is a tube, which is what holds the air. Tubes are inexpensive and easily replaceable, making most flat tires a quick fix.

Tire Pressure

A bicycle tube can expand like a balloon to many times its size when inflated, but when it rests inside a clincher tire, it provides outward force to the inside of the tire that is stronger than the weight of the bicycle and rider. PSI, or pounds per square inch, is a measure of this pressure. Since different tires, bicycles, and loads exert different forces on a bicycle tire, the optimal PSI is different for every bike.

Contact Patch

Air in a bicycle tube pushes outward equally on all sides of the tire and rim. Because of this, the base of the tire where it contacts the road is where the air is pushing directly downward against the road surface. This point is called the contact patch, where the tire is flat against the road surface. The PSI of the tire must equal the weight placed against the tire, so the size of the contact patch will be the weight load divided by the air pressure, approximately. If the bicycle and rider weigh 200 pounds, each tire supports 100 pounds of weight. Thus, a 1-inch wide tire inflated to 100 PSI will have a contact patch of about 1 inch. Wider tires require lower PSI to maintain a contact patch since there's more contact width-wise.

Determining Optimal PSI

An optimally inflated tire will give a visual cue for the best inflation. After filling a standard 700c tire to a low PSI of around 50, check the tire under the weight of the bicycle and rider. The tire should bulge visibly under the weight of the rider and bicycle. If it doesn't deflect at all above the contact patch, it's over-inflated. An over-inflated tire gives a harsher ride and is prone to bouncing on rough terrain, interrupting traction. An under-inflated tire will deflect too much, allowing the rim to contact the inside of the tire or place pressure on the sidewalls. An under-inflated tire is prone to pinch flats and can even come off the rim while cornering. Follow the manufacturer's guidelines for PSI, but use visual cues while riding to determine if your tires are over- or under-inflated.

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