CALCULATOR · PRESSURE
Bike tire pressure calculator for road and gravel
Enter your weight, the bike's weight and the tire width to get a starting pressure for each wheel, in psi and bar. It uses Frank Berto's 15% tire drop method: 84 kg in all on 28 mm tires gives 59 psi front and 74 psi rear. It suits road and gravel. For MTB this method does not hold.
Total weight: 84 kg. A starting point. Stay within the range marked on the tire and rim.
This comes out above 5 bar: check the maximum for your rim and tire, above all on hookless rims. If it is over, use the maximum or a wider tire.
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Tire pressure chart by width and weight
The weight is the total: rider, bike, bottles and anything you carry. Each cell gives front and rear pressure.
| Width | 70 kg in all | 85 kg in all | 100 kg in all |
|---|---|---|---|
| 25 mm | 59 / 74 | 73 / 91 | 88 / 109 |
| 28 mm | 48 / 61 | 60 / 75 | 72 / 90 |
| 30 mm | 43 / 54 | 53 / 67 | 64 / 80 |
| 32 mm | 38 / 48 | 47 / 59 | 57 / 71 |
| 35 mm | 32 / 40 | 40 / 51 | 49 / 61 |
| 40 mm | 24 / 31 | 31 / 40 | 38 / 48 |
| 45 mm | 19 / 25 | 25 / 32 | 30 / 39 |
Where the formula comes from
Frank Berto measured 50 road tires at 7 pressures and 8 loads, and looked for the pressure at which each tire sags by 15% of its width under load. He published the result as a chart. Dave Adams later fitted a curve to that chart, and that curve is what this calculator uses:
psi = 153.6 × pounds on the wheel ÷ (width in mm)^1.5785 − 7.1685
To check it, this table compares the values Berto gives in his article for 100 pounds (45.4 kg) on each wheel with what the formula returns. The largest gap is 4 psi.
| Width | Berto | Formula |
|---|---|---|
| 19 mm | 136 psi | 140 psi |
| 20 mm | 126 psi | 129 psi |
| 23 mm | 106 psi | 102 psi |
| 25 mm | 88 psi | 88 psi |
| 28 mm | 76 psi | 73 psi |
| 32 mm | 60 psi | 57 psi |
| 37 mm | 46 psi | 44 psi |
How far it goes
- MTB. Berto himself doubts the 15% rule holds for mountain bike tires: knobs complicate the measurement, and riders there want grip at low pressure. That is why the calculator takes 23 to 50 mm.
- 15% is a convention. Berto says 13% feels harder and 17% more comfortable. Jan Heine of René Herse points out that the figure came from tire makers' recommendations and from no test of Berto's own.
- Tubeless. Schwalbe says you can run slightly less pressure and gives no figure. Neither do we: the calculator takes nothing off.
- Supple tires. They sag more at the same pressure and would need more to reach 15%, according to René Herse, which adds that pressure changes their performance little.
How to use the number
- Weigh yourself holding the bike, ready to ride: that is the figure Berto asks for. If you cannot, add your weight and the bike's.
- Measure the real width with the tire fitted if you can. The label and the real width do not always match, and a few millimetres shift the curve a lot.
- Inflate with a gauge. Schwalbe warns that a thumb is no use: from about 2 bar, every tire feels hard.
- Ride and adjust. If it bounces on broken surfaces, take a little out. If the tire squirms in corners or you feel the rim, add some. That is practical judgement, with no validated number behind it.
- Check it at least once a month. Schwalbe treats losing 1 bar a month as normal, and asks for a check before every ride with latex tubes.
In Pedalytics
Pedalytics is not out yet: it is listed as «Coming soon». The Prepare ride checklist includes a quick pressure and brake check, and each tire's wear is tracked on its own. What you can use today is this calculator and the guide to how long tires last.
Frequently asked questions
What pressure should I run on a road bike with 28 mm tires?
With a 75 kg rider and a 9 kg bike, the calculator gives 59 psi front (4.1 bar) and 74 psi rear (5.1 bar). It is a starting point: adjust it within the range marked on the tire and the rim.
Why does the rear tire need more pressure?
Because that wheel carries more weight. Berto works with a split of 45% front and 55% rear in a sporty position.
What pressure should I run on gravel with 40 mm tires?
With a 75 kg rider and an 11 kg bike it gives 32 psi front (2.2 bar) and 40 psi rear (2.8 bar). That is beyond what Berto measured, so use it as a reference and go lower on rough ground, without dropping below the sidewall minimum.
Does it work for tubeless?
It gives the same pressure as with a tube. Schwalbe says tubeless can run slightly lower and gives no figure, and this calculator applies no discount.
Does it work for MTB?
No. Berto doubts the 15% rule holds for mountain bike tires, so the calculator stops at 50 mm and gives no figure above that.
Sources
Pages read when this text was written or revised, on 3 November 2026.
- Berto. All About Tire Inflation. Frank Berto, copia publicada en Velonerd.
- Bike Tinker. Optimal Tire Pressure for bicycles. Bike Tinker, 2010 (fórmula de Dave Adams).
- René Herse. Tire Pressure Take-Home. Jan Heine, René Herse Cycles, 2016.
- Schwalbe. Tire Pressure Bike Tires. Schwalbe, preguntas técnicas.
- Schwalbe tubeless. Tubeless. Schwalbe, preguntas técnicas.