Road bike tyre pressure
There is no tyre pressure calculator here, on purpose: no maker publishes a formula we could reproduce, and a curve we fitted ourselves would be an invented formula.
What the published rule says
Frank Berto measured 50 road tyres at seven pressures and eight loads and proposed inflating to the pressure at which the tyre drops by 15 % of its width under load: 13 % is firmer, 17 % softer. The only numbers he printed, for a 90.7 kg (200 lb) rider and bike, with about 45 % of the weight on the front wheel and 55 % on the rear, are:
| Tyre | Pressure |
|---|---|
| 700×19C | 136 psi |
| 700×20C | 126 psi |
| 700×23C | 106 psi |
| 700×25C | 88 psi |
| 700×28C | 76 psi |
| 700×32C | 60 psi |
| 700×37C | 46 psi |
Source: Frank Berto, All About Tire Inflation (2006). His full chart is a graph, not an equation; front about 10 % lower, rear about 10 % higher.
Why modern advice is lower
Berto measured 1990s clinchers. Jan Heine later called the 15 % an arbitrary value taken from manufacturers' recommendations rather than from testing (Rene Herse, Tire Pressure Take-Home), and SILCA says the Berto chart typically leaves the front tyre under-inflated and ignores the road surface (SILCA). Today's calculators also ask for the inner rim width, tubeless or not, hooked or hookless rims and the surface, because a wider rim gives the same tyre more volume.
Calculators that publish their inputs
- SRAM / Zipp: ride type, surface, system weight, tyre width, casing, wheel diameter, rim type and inner rim width.
- SILCA: weight, tyre, rim and surface.
Neither publishes its formula. Your tyre maker's own table, where there is one, is the next best guide.
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