Bike Tyre Pressure Calculator

For a 75 kg rider on a 9 kg bike with 28 mm tyres on smooth tarmac, this calculator suggests about 66 psi front and 71 psi rear with tubes on a 21 mm rim. A narrower tyre, a heavier rider or a narrower rim all raise that. Enter your own setup above, because a few millimetres of width change the answer more than most riders expect.

It starts from Frank Berto's 15% tyre-drop rule: a tyre should compress by about 15% of its height under load. The load on each wheel and the mounted tyre width give a base pressure. We then adjust it for surface, tubes versus tubeless and wheel size, and apply any rim limits. The results page shows each adjustment.

The rear wheel usually carries 55% or more of the combined weight of you and your bike. On a typical road bike the front runs about 7% lower. It doesn't fall further because braking moves weight forward, and the front tyre needs to stay stable when that happens.

Only slightly. Tubeless removes the friction between tube and tyre and rules out pinch flats, so you can run a little less air safely. We suggest about 5% less than you'd run with an inner tube. The pressure that rolls fastest barely changes, which is why we don't take off more.

A hooked rim has a small lip that grips the tyre bead. A hookless rim has straight walls, and the tyre is held on by air pressure alone, so it only works with tubeless-ready tyres and has a firm pressure limit. We only ask when you pick tubeless. Many newer tubeless road and gravel wheels are hookless, so check the wheel's spec page. If you ride with inner tubes, you can skip it.

The widely used limit is 5 bar (72.5 psi) for 25 to 29 mm tyres, and it drops as tyres get wider: 4.5 bar from 30 mm, 4 bar from 35 mm, 3.5 bar from 40 mm and 3 bar from 45 mm. Your rim or tyre maker may set a lower limit, and that one takes priority. Enter it under fine-tuning and the calculator will respect it.

A little. A softer tyre grips better on wet roads, so many riders take off a few psi. We don't ask about the weather because any figure would be a guess. Start with a couple of psi less than the number above, and add some back if the tyre feels vague in corners.

Yes. Pump a tyre to 70 psi in a 20°C hallway and ride at 3°C, and it drops to around 65 psi. The calculator can work out what to pump to, so your tyres reach the right pressure on the road. Enter both temperatures under fine-tuning.

Pressure falls roughly with the square of width, so a small change in width means a noticeable change in pressure. The label isn't always accurate either: real widths vary by model and grow on wider rims. We estimate your mounted width from the sidewall size and rim, but a caliper measurement is more accurate and you can enter it under fine-tuning.

Treat it as a well-informed starting point. We checked six setups against the SILCA and Rene Herse averages implied by a published comparison, and the rear pressure landed within 15% each time. Rider preference, tyre construction and your pump's gauge can each shift the ideal by a few psi, so test a few pressures on a road you know.