Tire Growth Calculator

Compare static tire rollout with measured running rollout, or infer effective rollout from road speed and engine RPM. Measured rollout mode opens by default.

All Calculators

Running rollout source

Static tire circumference / rollout (in)

Measured running circumference (in)

Road speed for inferred mode (mph)

Engine RPM at that speed

Primary reduction ratio for inferred mode

Engaged transmission gear ratio for inferred mode

Front sprocket teeth for inferred mode

Rear sprocket teeth for inferred mode

Results update as you type.

Results

Inferred rollout assumes a locked clutch, no tire slip and accurate synchronized speed/RPM measurements. Clutch slip, wheelspin and measurement error can appear as apparent growth or shrinkage. Use independent road speed; a wheel-derived speed signal can be circular. Measured running circumference must come from a suitable measurement method; do not approach a rotating tire.

Formula and assumptions

Diameter = circumference ÷ π. Growth % = (running ÷ static − 1) × 100. Inferred circumference (in) = mph × 1056 × overall reduction ÷ engine RPM. Overall reduction = primary × gear × rear/front.