Bike tyre pressure
Starting front and rear tyre pressures from your weight, the bike, the weight split, tyre width, construction and surface — from Frank Berto's 15% tyre-drop measurements, with every step of the working shown and the rim and tyre limits applied.
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How to use it
Enter the rider, bike and luggage weights, how the weight splits between the wheels, the tyre (measure its width once mounted — it is often wider than the label says), whether it runs with a tube, tubeless or as a tubular, the surface, and the rim. The tool gives a front and rear pressure in bar and psi and shows how it got there.
The model. In the 1990s Frank Berto measured how far tyres of each width compress under load, and charted the pressure that gives a 15% tyre drop — the tyre squashed by 15% of its height. Jan Heine (Bicycle Quarterly, "Optimizing Your Tire Pressure for Your Weight", reviewed by Berto) found that this is close to the point where a tyre stops getting faster as you add pressure: below it, it rolls slower; above it, it is no faster, only harsher. The chart has one straight line per tyre width (20, 23, 25, 28, 32 and 37 mm), pressure against wheel load. The lines here were digitised from that chart and reproduce its worked example: 100 kg split 45/55 gives 125/155 psi on 20 mm tyres and 45/53 psi on 37 mm tyres.
The working:
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Total weight = rider + bike + luggage.
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Wheel loads from the weight distribution. Heine’s measured splits are 45/55 for a randonneur bike with a front bag, 40/60 for a racing bike and 35/65 for a city bike with a rear load; weigh yours with a bathroom scale under each wheel for the real numbers.
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Berto’s pressure for that load and width — interpolated between his lines for widths in between, extrapolated beyond them (below).
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Adjustments, rules of thumb and not part of Berto’s data: −5% tubeless (no tube to pinch); surface +5% for very smooth tarmac or the track, −5% rough roads, −10% smooth gravel, −15% rough gravel and trails. Heine suggests a little more on very smooth roads and less on rough or unpaved ones; the percentages are this tool’s.
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Limits: the lower of the tyre’s and the rim’s maximum, and 5 bar (72.5 psi) for hookless rims (the ETRTO / ISO 4210 limit for hookless road rims).
The chart plots all of Berto’s lines with yours highlighted and the front (F) and rear ® wheels marked. Your units are remembered and shared with the other bike tools.
Limits
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It is a starting point. Try ±5–10% and keep what feels and rolls best; on rough ground lower is often faster.
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Berto measured 20–37 mm road tyres. For wider gravel and mountain-bike tyres the 37 mm line is extended with contact-patch scaling (at a fixed 15% drop the patch grows about as width^1.5, so pressure falls as width^−1.5). It gives sensible numbers but is not measured; casings, inserts and riding style matter more there.
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Loads outside about 27–70 kg per wheel extend the lines straight.
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Never exceed the maximum printed on the tyre or the rim — whichever is lower — and observe the minimum on the tyre; very low pressures with an inner tube invite pinch flats.
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The rim width changes the tyre’s shape and volume; a tyre on a wide rim may need a little less.
Related: gearing calculator, power and climbing, spoke length, maintenance log.
Linking to an example
Weights are read in the units the link (or the visitor) uses: kg with units=metric, lb with
units=imperial; tyre and rim maxima in bar or psi likewise.
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Rider, bike, luggage and bottles |
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Front share (%), with |
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Measured width (mm) |
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Tyre and rim maximum pressure |
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Presets (?example=<name>; these use kg):
example= |
Shows |
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Heine’s worked example: 100 kg, 45/55, 20 mm tyres → about 125 / 155 psi |
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the same 100 kg on 37 mm tyres: about 45 / 53 psi |
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75 kg rider, 9 kg road bike, 700 × 28 clinchers |
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80 kg, 10 kg gravel bike, 45 mm tubeless on smooth gravel, hookless rims |
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85 kg, 14 kg trail bike, 29 × 2.4 tubeless on singletrack (extrapolated) |
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114 kg on 25 mm tyres and hookless rims: the 5-bar limit applies — go wider |
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