How tire pressure is calculated
- Your weight and the bike’s weight are added together. If you leave bike weight empty, 8 kg is used.
- That total is split 45% on the front wheel and 55% on the rear.
- Each wheel’s pressure in bar = load on that wheel (kg) × a coefficient ÷ tire width (mm). The coefficient depends on the surface and tire type, for example 3.7 for road clinchers and 3.1 for road tubeless. Gravel and MTB use lower coefficients.
- The result is shown in bar (rounded to 0.1) and psi (rounded to a whole number; 1 bar ≈ 14.5 psi).
Example: a 75 kg rider on an 8 kg bike with 25 mm road clinchers. The total is 83 kg: 37.35 kg on the front wheel and 45.65 kg on the rear. That gives 5.5 bar (80 psi) front and 6.8 bar (98 psi) rear.
The model does not account for altitude, temperature or rim width, which can each shift the ideal pressure by about 0.2–0.5 bar. Use the result as a starting point and fine-tune by feel. Never exceed the maximum pressure printed on your tire or your rim; always stay below the lower of the two.
Frequently asked questions
Why is the rear pressure higher than the front?
About 55% of the combined weight of you and your bike sits on the rear wheel, so the rear tire needs more pressure to carry it.
Should tubeless tires run lower pressure?
Yes. For the same rider and tire width, the calculator gives tubeless tires about 16% less pressure than clinchers on road and gravel, and about 14% less on MTB. In the example above, road tubeless gives 4.6 bar (67 psi) front and 5.7 bar (82 psi) rear.
How does tire width change the pressure?
Pressure is inversely proportional to tire width. Going from 25 mm to 28 mm lowers it by about 11%: in the example above, from 5.5/6.8 bar to 4.9/6.0 bar.
Can I go above the maximum pressure printed on the tire or rim?
No. The calculator doesn’t know the limits of your tire or rim. Always stay below the lower of the two maximums; hookless rims in particular often have a lower limit. If the result is above that limit, use the limit or consider a wider tire.