Why does rollout matter?

Your bike computer converts wheel revolutions to distance using the rollout value. An incorrect value means inaccurate speed and distance readings. Even 10mm difference causes a 0.5% error, which adds up over long rides.

How do I do a manual rollout test?

With your full riding weight on the bike, mark the tyre and ground at the valve. Ride in a straight line for exactly one wheel revolution. Measure the distance between marks. This is your actual rollout distance.

Does tyre pressure affect rollout?

Yes, lower pressure causes more tyre deformation, slightly reducing the effective circumference. The effect is small (typically 1-5mm) but measurable. Higher pressure gives a more round tyre shape and slightly larger rollout.

Do different tyre brands have different rollouts?

Yes, even at the same nominal size (e.g. 700x25), different brands and models vary by 5-15mm due to differences in actual tyre dimensions, casing construction, and tread thickness.

BikeCalcs

Tyre Rollout Calculator

Calculate wheel circumference for accurate bike computer setup.

Tyre SizeSelect size or enter custom dimensions

Tyre Brand/ModelSelect brand or enter measured rollout

Inflation Pressure

Applied gas pressure

How We Calculate This

ETRTO Standard

Circumference = PI x (Bead Seat Diameter + 2 x Tyre Width). This gives the theoretical circumference from ISO/ETRTO tyre dimensions.

Adjustments

The calculator adjusts for tyre brand (measured values), inflation pressure (lower = smaller rollout), and rider weight (heavier = more deformation = slightly smaller rollout).

Frequently Asked Questions

Last updated: 2026-03-01

All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.