Road Tires
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 Tires
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.
Rider Weight
Larger riders compress bicycle tires more than average, increasing the pressure inside the tires. These riders may experience tire blowouts if running high pressures.
Environment
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.
Considerations
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.
