Bike Tyre Pressure Calculator

The method, and where the numbers come from

This isn't a made-up formula. Each step is based on published testing, and the sources are listed at the end so you can check them yourself.

1. Your weight becomes a load on each wheel

Pressure follows load, so the calculator uses your total system weight (rider + bike + bottles + kit), not just body weight. That load is split roughly 45% front / 55% rear, the distribution Frank Berto used, which is why the tool gives the front a softer number than the rear.

2. The baseline: 15% tyre drop

The target is 15% tyre drop, the amount a loaded tyre should squash down. Berto measured 50 tyres across seven pressures and eight loads and found that a drop of about 15% of the tyre's width is the sweet spot between rolling resistance, grip and comfort. The calculator reads the 15%-drop pressure for your tyre width from his published data, then scales it to your weight. Wider tyres need less pressure for the same drop, which is why a 32 mm tyre sits far below a 25 mm one. SILCA's widely used calculator is built on the same 15%-drop principle.

3. Surface: rougher roads want lower pressure

Above a certain pressure the tyre stops absorbing the surface and starts bouncing over it, and that vibration actually slows you down, an effect SILCA calls the impedance "breakpoint". A 2025 study in the Journal of Science and Cycling confirmed the trade-off: no single pressure minimises both rolling resistance and vibration at once. So the rougher the surface you pick, the more the calculator eases the pressure down, and because road roughness is never exact, that choice widens the recommended range rather than shifting a single number.

4. Tubeless and hookless safety limits

Tubeless tyres have no inner tube to pinch, so they can safely run about 10% lower, which the calculator applies when you tick the box. Hookless rims have a hard ceiling: the ISO/ETRTO standard maximum is 72.5 psi (5 bar), enforced by brands like Zipp, and exceeding it can blow the tyre off the rim. Select a hookless rim and the tool caps its recommendation at that limit and tells you to fit a wider tyre instead of over-inflating.

5. Why a range and a confidence score, not a fake-exact PSI

Berto himself stressed the numbers "aren't precise", and the 2025 research shows the ideal is a compromise, not a single point. So the tool shows a useful band, its confidence in it, and the biggest source of uncertainty (usually your true front/rear weight split, which we estimate rather than measure). A precise-looking single number would be less honest, not more.

What this tool doesn't do

Berto's tested data covers road tyres to 37 mm. Gravel widths and the surface and tubeless adjustments are reasonable extensions of his method, not separately lab-tested, so they're a well-founded estimate. Mountain-bike tyres are a different problem (traction over rolling resistance) and aren't covered. It also can't know your specific tyre casing or your exact weight distribution, both of which shift the ideal pressure.

Sources

• Berto, F. All About Tire Inflation (2006), based on his 15% tyre-drop testing for Bicycling magazine, developed with tyre engineers at Michelin, Continental and IRC. The baseline pressures and the 45/55 weight split come from here.
• Welburn, A. J., Bailey, S. J. & Ferguson, R. A. (2025). The Impact of Tyre Width, Pressure and Surface Condition on Rolling Resistance and Vibration Transmission of Bicycle Tyres. Journal of Science and Cycling. Basis for the surface handling and the "no single optimum, use a range" approach.
• SILCA, Tire Pressure Calculator Explained, on the impedance breakpoint and why staying slightly below it is safer than going above.
• SRAM / Zipp, Hookless Tyre Compatibility, and the ISO/ETRTO 72.5 psi (5 bar) hookless maximum used for the safety cap.