Tire pressure calculator for road and gravel

How the calculator works

The short version: it inflates each tire so it squashes by about 15% under its share of your weight, then nudges the result for surface and setup, then applies hookless limits. The long version, with the sources, is below. This is a research-based model. We have not validated it with our own roll-down or lab tests, and no calculator knows your exact tire.

1. The core: Berto's 15% tire drop

Frank Berto, long-time engineering editor at Bicycling, measured 50 tires at seven pressures and eight loads and plotted the pressure that gives a 15% tire drop for each width and load. He described 15% as the best compromise between rolling resistance, comfort and cornering, based on discussions with tire engineers; 13% gives a harder ride, 17% a softer one. Bicycle Quarterly republished the chart and is explicit that its loads are per wheel, not for the whole bike. Rene Herse notes the 15% figure itself came from manufacturer recommendations rather than testing, and that supple tires deflect more than stiff ones at the same pressure. It is a sensible target, not a law of physics.

We use a published curve fit of Berto's chart:

P = 600 × L / W² + 0.75 × W − 25

where P is pressure in psi, L is the load on that wheel in pounds, and W is the tire's actual width in mm. This fit is the core of BikeLab Studio's 2026 pressure model, which states an accuracy of about ±2 psi against the chart within its domain.

We checked it ourselves against the values Berto printed for a 100 lb wheel load:

So: within about 3.5 psi from 23 to 37mm, and poor below 23mm, where it reads high (the calculator tells you). Bicycle Quarterly's worked example (100 kg system, 45/55 split, 37mm tires: 45 / 53 psi) comes out at 46 / 56 psi.

2. Loads per wheel

Rider plus bike weight is split between the wheels. Bicycle Quarterly measured about 45/55 (front/rear) on a randonneur bike and 40/60 on a racing bike; Berto used 45/55 for a rider on the drops. By default the rear gets 55% and the front is set to 93% of the rear pressure, a coupling BikeLab calibrated against SILCA's and Rene Herse's calculators, on the grounds that the front carries far more than its static share under braking. Choose a Berto static split if you prefer the original method, which gives a noticeably softer front.

3. Actual width from rim width

If you do not enter a measured width, we estimate it with the ETRTO rule of thumb Vittoria publishes: ±0.4mm of tire width per 1mm of rim width away from the tire's design rim. We assume a 19mm design rim for tires up to 28mm (Vittoria's own example for a 28-622 tire) and 21, 23 and 25mm for 29 to 34, 35 to 46, and 47mm-plus tires, following the ETRTO 2020 pairings BikeRadar prints. Those design-rim assignments are our assumption, and ETRTO allows a manufacturing tolerance on top (±2mm in Vittoria's 28mm example). Bicycle Rolling Resistance measured 0.425mm per mm on road tires and 0.3mm on gravel tires, so the rule is a fair middle.

4. Surface and setup adjustments

5. Hookless limits

With "hookless" selected, results are capped at 5 bar / 72.5 psi for tires up to 29mm and 4.5 bar / 65 psi for 30 to 34mm, the ETRTO figures as reported by TOUR. For 35mm and wider we warn (without capping) if you exceed the published hookless maximum for that width: 4 bar (58 psi) for 35 to 39mm, 3.5 bar (51 psi) for 40 to 44mm, 3 bar (44 psi) for 45 to 54mm and 2.5 bar (36 psi) for 55mm and up. These are Schwalbe's figures, and they match the ISO table of straight-side rim pressures reproduced by Bicycling. Bicycling's article text gives 43.5 psi for 40mm tires, but its own reproduced table puts 43.5 psi (300 kPa) at 45 to 54mm, so we use the table. The table also lists 5.5 bar for 18 to 24mm tires. Those widths are below every hookless minimum, so we cap them at 5 bar. We also warn if your tire is narrower than the minimum for your rim. At each rim width we use the stricter of two sources: TOUR's report of the 2023 ETRTO update (25mm up to 21mm internal, 28mm for 22 to 24mm, 29mm for 25mm) and the ISO "Table 7, Recommended rim widths" reproduced by Bicycling (25mm for 21 to 22mm, 28mm for 23mm, 29mm for 24 to 25mm, narrower below 21mm). That gives 25mm up to 21mm internal, 28mm for 22 to 23mm and 29mm for 24 to 25mm. The only row where they differ is 24mm: TOUR puts it at 28mm and Table 7 at 29mm, and Table 7 may not be specific to hookless rims. Above 25mm we show a note rather than a warning: Table 7 lists 35mm tires as the narrowest for 26 to 27mm rims, 47mm for 28 to 30mm and 58mm for 31 to 35mm, but no hookless-specific source we found confirms those. We have not verified any of these against the ETRTO or ISO text. ENVE states the 25mm-rim figure (29mm minimum) itself. Your rim maker's chart comes first. When capped, the calculator shows what the method wanted, because the honest answer is usually a wider tire.

How it compares

For 85 kg of rider plus bike on 40mm tubeless tires, a 25mm rim and the gravel setting, the calculator gives 35 / 37 psi. Vittoria's calculator, as published by BikeRadar, gives 33.0 / 34.8 psi for the same weight on mixed terrain. For road, BikeLab's paper lists SILCA at 70 / 71.5 psi for an 83 kg rider on 28mm tires and a 21mm rim; ours gives about 65 / 69 psi for that case. Close enough to be useful, different enough to remind you these are all models.

Limits you should know about

• Berto's chart covers roughly 19 to 37mm tires measured in the 1990s. Above 37mm the formula is extrapolating.
• Casing stiffness is not an input. Supple race tires and stiff, puncture-protected tires behave differently at the same pressure (Rene Herse).
• Pressure scales in a straight line with load. For heavier riders this gives firmer numbers than calculators that flatten out, such as the Vittoria figures above.
• Your pump gauge may be off. Berto found gauges tend to read high as they wear; BikeRadar quotes SILCA's Josh Poertner putting a typical floor pump at about ±5%.
• Not for mountain bikes. Berto himself said the 15% criterion does not suit MTB tires.

Riding hookless wheels? Before you set pressure, make sure the tire itself is approved for your rim: our list of hookless-compatible road tires pulls the brand and rim-maker approvals into one place. More guides are on the guides page.

Sources

1. Frank Berto, All About Tire Inflation (2006). https://d-a-v-e.org/campusebikes.com/documents/Tireinflation.pdf
2. Jan Heine, Optimizing Your Tire Pressure for Your Weight, Bicycle Quarterly reprint. https://www.renehersecycles.com/wp-content/uploads/2015/03/BQTireDrop.pdf
3. Rene Herse Cycles, Tire Pressure Take-Home. https://www.renehersecycles.com/tire-pressure-take-home/
4. BikeLab Studio, A Constant-Deflection Model for Road and Gravel Tire Pressure (June 2026). https://www.bikelabstudio.com/articles/white-paper-psi-model.html
5. Vittoria, Vittoria is a member of ETRTO (design rim width, 0.4mm rule). https://int.vittoria.com/blogs/magazine/vittoria-is-member-of-etrto
6. Bicycle Rolling Resistance, The Rim Width Test. https://www.bicyclerollingresistance.com/specials/rim-width-test
7. BikeRadar, Gravel bike tyre pressure explained (Nov 2025). https://www.bikeradar.com/advice/workshop/gravel-tyre-pressure
8. SRAM, Talking Tire Pressure for Zipp Wheels. https://www.sram.com/en/life/stories/talking-tire-pressure-for-zipp-wheels
9. TOUR, Hookless rims on road bikes: background and facts (May 2024). https://www.tour-magazin.de/en/impellers/explosive-mix-hookless-rims-on-road-bikes-background-and-facts/
10. Bicycling, Are Hookless Wheel Systems Safe on the Road? (reproduces ISO Table 7, Recommended rim widths, and the straight-side pressure table; Table 7 may not be hookless-specific). https://www.bicycling.com/bikes-gear/a60129869/are-hookless-wheel-systems-safe/
11. ENVE, Hookless Rim Technology 101 (29mm minimum on 25mm internal rims). https://enve.com/blogs/journal/hookless-rim-technology-101
12. Schwalbe, Hookless rims FAQ (maximum pressure by tire width). https://www.schwalbetires.com/technology-faq/hookless-rims/
13. Continental, Hookless vs. Hooked Rims. https://www.continental-tires.com/us/en/tire-knowledge/hookless-vs-hooked-rims/