Speedometer error estimate

Estimate road speed from indicated speed when only the theoretical tire diameter changes.

Calibration reference

New labeled size

Geometric speed estimateEnter values to calculate

Distance per revolution changes

If the assumed reference calibration is exact, a larger rolling circumference travels farther per wheel revolution. The formula scales indicated speed by the diameter ratio.

Real rolling radius varies

Wear, pressure, load, vehicle calibration and legal tolerances can change the relationship. Use proper instruments and manufacturer procedures for calibration.

More tools

Tire dimensions

Calculate theoretical diameter and circumference.

Tire comparison

Compare the geometry of two metric tire labels.

RPM & road speed

Relate speed and RPM through tire and gear ratios.

Two-stroke mix

Calculate oil from a manufacturer-specified ratio.

Wheel offset

Compare inner clearance and outer wheel position.

Compression ratio

Calculate static ratio from cylinder and clearance geometry.

Engine displacement

Calculate total displacement from bore, stroke and cylinders.

Power to weight

Compare horsepower and vehicle weight in common units.

Sprocket ratio

Find chain-drive ratio and driven sprocket RPM.

Injector size

Estimate per-cylinder fuel flow from explicit assumptions.