Calculate Speed vs RPM and RPM vs Speed for your car. Determine your ideal gearing for the racetrack and road, or check your speedometer error for your new final drive ratio and tyres.

Race Ratio produces detailed tables for each gear at 100rpm or 5kmh/mph intervals. It allows you to compare up to three different combinations of final drive ratio and tyre size at a time, and will accept radial tyre sizes or your own tyre circumference measurements for greatest accuracy.

Select from Race Ratio's database of pre-loaded makes and models, or input and save your own custom car gearing.

Race Ratio supports measurements in metric and imperial units, and accepts up to eight gearbox ratios per car.

Best of all, Race Ratio travels wherever your iPhone does, so you can fine-tune your gearing between racetrack sessions or check out your highway gearing in the middle of a drive.