Tire Size Comparison
Compare two tyre sizes: diameter, circumference, difference and speedometer error.
Inputs
mm
%
in
mm
%
in
Results
- Diameter difference
- 0.38 %
- Current diameter
- 631.9 mm
- New diameter
- 634.3 mm
- New circumference
- 1,993 mm
- Actual speed at 100 km/h indicated
- 100.4 km/h
Formula
Diameter = rim × 25.4 + 2 × width × aspect
Actual speed = indicated × new diameter ÷ current diameter
Assumptions & limits
- Nominal sizes; real tyres vary by brand and tread wear.
Worked example
205/55R16 = 631.9 mm; 225/45R17 = 634.3 mm → +0.38%.