Bicycle tire pressures vary dramatically based on tire type, size, materials and performance requirements. While it is not imperative that you fill tires to exact levels, getting the right pressure range is essential to safety and comfort. Check the sidewall of your tire for a recommended pressure range. Tire pressure is measured in pounds per square inch (psi), or bar.
Road bicycle tires have small internal volumes and generally accommodate pressures from 90 to 120 psi, or 6 to 7 bar. Racing and high performance tires may use higher pressures.
Mountain bike tires are much larger than road tires and have lower pressures, ranging from 30 to 60 psi, or about 2 to 4 bar.
Larger riders compress bicycle tires more than average, increasing the pressure inside the tires. These riders may experience tire blowouts if running high pressures.
Tire pressures should be adjusted to suit riding environments. Many riders prefer softer tires to provide larger gripping surfaces in wet weather. Tour riders must often use lower pressures to make up for the expansion of air heated by road friction.
Low air pressures in bicycle tires increase rolling resistance and are generally undesirable in race situations. However, low pressures may be used to give handling and stability benefits in certain road and track conditions.