🛞 Bike Wheel Circumference Reference
Select your tire size to find its standard circumference value — commonly used for calibrating a cycling computer or GPS bike computer's wheel-size setting.
Where the numbers come from
The chart holds the published calibration values, but each one traces back to the same geometry - the rim's bead seat diameter plus two tyre heights, turned into a circumference:
C = π × (bead seat diameter + 2 × tyre width)
BSD: 622 mm for 700c and 29er, 584 mm for 27.5", 559 mm for 26"A 700x25C works out at π × (622 + 50) = 2111 mm, and the chart lists 2105. The 6 mm difference is the tyre squashing under a rider, which is why the published figures sit slightly under the pure geometry. The same sum explains why a 29 x 2.10 reads 2288 mm and a 26 x 1.90 only 2050: same tyre, 63 mm of rim.
Calibrating a computer
- The chart is accurate to about 1%. On a 10 km ride that is 100 m of drift, and it compounds identically on every speed reading.
- Roll out for better. Sit on the bike at your normal pressure, line the valve up with a floor mark, roll forward one revolution and measure between the marks in millimetres.
- Printed width is nominal. A 25C tyre on a modern 21 mm internal rim measures nearer 27 mm, so it rolls larger than the chart says.
Frequently asked questions
What wheel circumference should I enter for 700x25c?
2105 mm as a starting point. Roll the wheel out yourself if you want the distance to match a mapped course closely; heavier riders and lower pressures both pull the real figure a few millimetres down.
How do I measure my bike wheel circumference?
Mark the floor at the valve, roll forward with your weight on the bike until the valve returns to the bottom, mark again and measure the gap. Average two attempts - a centimetre of error is half a percent.
Does tyre pressure affect wheel circumference?
Yes, by a few millimetres. Dropping from 90 psi to 60 psi flattens the contact patch enough to shorten the rollout, and a worn tyre is smaller than a new one.