Speedometer Error & Tire Size Calculator

Compare indicated vs GPS speed, or see how a tire size change affects your speedometer reading.

Indicated Speed (mph)

GPS Speed (mph)

Speedometer Error

+3.33 %

Actual Speed at 60 indicated

58.0 mph

Want to understand the numbers?

Read the step-by-step guide, worked example and common questions for this calculator.

Gearing & Top Speed

Find your theoretical top speed from engine RPM, gear ratios, sprockets, and tire dimensions.

Chain Length

Get the right chain link count from sprocket sizes, centre distance, and chain pitch.