One of the tools I use very much for testing my cars, is the Mini 4WD Speed Checker. The dyno is designed for the Tamiya Mini 4WD, but it can be used for any mini scale R/C car, slot cars, Magracers, any electric car that fit.
It is good to compare and measure different car setups and see what improve the speed.
You can buy the speed checker at Amazon. Tamiya Speed Checker TAM15183