About this calculator

What it does

It gives a starting tire pressure for cyclocross, front and rear, in psi and bar. You set your weight, your tire (tubular, tubeless or tube), the ground (dry or hardpack, greasy or wet grass, mud, or deep mud, sand or snow), whether the course has roots, rocks or frozen ruts, and whether you run tire inserts (tubeless only).

How the numbers are made

The model is still under test, and the numbers will change.

Tubulars follow a fit to about 70 published race pressures from pros and experienced amateurs, with an adjustment for elite riders, who run lower than amateurs on firm ground. Held out of the fit, it came within 0.6 psi on average of three verified race pressures from a world-class rider.

Tubeless uses a hand-set rule for now: your weight in lb divided by 10, plus 6 psi, on dry ground. Inserts take it 2 psi lower, on thin evidence. The rule will be recalibrated from riders' own race logs.

Tubes use your weight in lb divided by 10, plus 14 psi.

For tubeless and tube, greasy grass is 1 psi lower, mud 3 psi lower, and deep mud, sand or snow 4.5 psi lower. Tubulars take their ground steps from the fit. Roots, rocks or frozen ruts add 2 psi. The rear is always 2 psi above the front.

The shaded band is plus or minus 2.5 psi, the model's typical miss for a new rider. Even top riders on the same course on the same day differ by about 2 psi.

The lowest pressures in the table are judgment, not data, and the band never goes below them. Riders under 115 lb are lighter than anyone in the data, so treat their numbers as a rough guide.

How to use it

The calculator gets you close. The pre-ride finds your number.

1. Set pressure with one digital gauge, the same one every time, and at the start line if you can. Pressure falls about 1 psi for every 9 °C (16 °F) colder, so a tire set in a warm garage reads low on a cold morning.
2. On the pre-ride, drop 1 psi a lap until you feel the rim, or the tire squirms or folds in a corner. Then go back up 1 psi.
3. Write down what worked, with the conditions, so next time starts closer.

What it cannot do

• Say where a tire will burp or the rim will strike. That depends on your rim and tire.
• Account for tread, casing, tire width or rim width. It assumes a tire about 33 mm wide.
• Replace the pre-ride.

It has not been validated on juniors.

Where the numbers come from

Published pressures from professional riders and mechanics (Cyclocross Magazine, Velo, Cyclingnews, and team and tire-maker pages), rider reports on cycling forums, and Helen Wyman's rule of thumb (road.cc, 2017) as a starting reference. No tire maker is involved, and nothing is sponsored.

Privacy

The calculator runs on your phone. Your weight and settings stay in your browser and are never sent anywhere. There are no cookies, no analytics and no accounts.