Ratio Calc is a quick and easy tool for radio control car racers to use trackside. Gear ratios are a vital part of R/C racing and knowing your final drive ratio (FDR) is very useful for both comparison with other racers and tuning purposes. This iPhone app lets you quickly select your car from a large list (470+ at the last count and regularly updated) by filtering on class, manufacturer and then model. Select your pinion and spur size and the FDR is displayed. Tyre diameter can also be entered to calculate your rollout.
Ratio and rollout charts are also available which plot pinion and spur gear combinations to create handy reference tables.
The app can be downloaded free from the App Store here: