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Bike Tire Pressure Calculator

This bike tire pressure calculator gives a starting front and rear pressure, in psi and bar, for road, gravel and mountain bikes, from your weight, tyre width, rim width, tubeless setup and the surface you ride.

Your bike and tyres

kg
mm
mm

Wider rims spread the tyre and need a little less pressure. Often printed on the rim or listed by the wheel maker.

Starting pressure

Front 28.1 psi, rear 34.3 psi

Front
28.1psi
1.94 bar
Rear
34.3psi
2.37 bar

Modelled at 40.0 mm wide on your rim. The rear carries more weight, so it needs more pressure.

A starting point based on the 15% tyre-drop method, not a limit. Never go above the maximum pressure printed on your tyre or rim. Adjust 2–3 psi at a time: lower for grip and comfort, higher if the tyre squirms in corners or the rim hits rocks.

How the pressure is worked out

  1. Split the rider + bike weight between the wheels: 45% front, 55% rear (42/58 on a mountain bike).
  2. Work out the tyre's real width on your rim: about 0.4 mm wider for each mm of rim above 19 mm (road), 23 mm (gravel) or 27 mm (MTB).
  3. Find the pressure that lets the loaded tyre drop about 15%, which rises with load and falls with width to the power 1.58.
  4. Take 5% off for tubeless, and 7% or 14% for rougher surfaces.

psi ≈ 150 × (2 × wheel load in kg) ÷ width in mm^1.58

Fine-tuning on the bike

  • Use the same floor pump or gauge each time; cheap gauges can be several psi out.
  • Change 2–3 psi at a time and ride the same stretch to compare.
  • Too soft: the tyre squirms in corners, feels vague or the rim hits rocks.
  • Too hard: the bike skips over bumps, loses grip and feels harsh.
  • Never go over the maximum printed on the tyre or rim.

Frequently asked questions

What tyre pressure should I run on a gravel bike?+

For an 80 kg rider plus bike on 40 mm tubeless tyres over mixed gravel, about 28 psi front and 34 psi rear; on 45 mm tyres about 23 / 28 psi. Go lower for loose or chunky surfaces, higher for mostly tarmac.

What pressure for 28 mm road tyres?+

About 56 psi front and 68 psi rear for an 80 kg system weight with inner tubes on smooth roads. Moving to 32 mm tyres drops that to about 45 / 55 psi with the same comfort margin. Tubeless lets you go about 5% lower.

What pressure for mountain bike tyres?+

For 85 kg on 2.4" (61 mm) tubeless tyres on mixed trails, about 14 psi front and 20 psi rear. Heavier riders, aggressive riding and rocky trails usually need a few psi more to protect the rim; tyre inserts let you run lower.

How does the calculator work?+

It uses Frank Berto's tyre-drop method: pump the tyre so that, with you on the bike, it compresses about 15% of its height. That gives a pressure in proportion to the weight on each wheel and falling steeply as tyres get wider. It then adjusts for rim width, tubeless and surface. It's a well-tested starting point that you then fine-tune by feel.

Is this the same as the SILCA or SRAM tyre pressure calculator?+

No. Those calculators use their makers' own models, which aren't published, and they ask about things like riding speed and tyre casing. This is an independent calculator using the published tyre-drop method, so expect its numbers to differ from theirs by a few psi. All of them give starting points, not exact answers.

Why is the rear pressure higher than the front?+

Most of your weight sits over the rear wheel: roughly 55–60% on road and gravel bikes. A tyre carrying more load needs more pressure to keep the same amount of compression, so the rear runs higher.

Does rim width change tyre pressure?+

Yes. A wider internal rim width spreads the tyre so it measures wider than the size printed on it, and a wider tyre needs less pressure. Enter your rim's internal width and the calculator widens the tyre by about 0.4 mm for each extra millimetre of rim.

What's the maximum pressure on hookless rims?+

72.5 psi (5 bar), under the ETRTO standard, and your tyre and rim makers may set a lower limit. Tick “Hookless rims” to get a warning if the suggested pressure goes over it.

How do I convert psi to bar?+

Divide psi by 14.5. For example, 40 psi is 2.76 bar and 80 psi is 5.52 bar. The calculator shows both.

Is anything I enter saved or sent?+

No. Everything is calculated in your browser and nothing is stored or uploaded.

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