[lincpimp]

I generally try to get my motor speed around 35k rpm. The neu motors can handle higher rpm, so you can most likely shot for 40k to 45k rpm. So you take the kv and multiply it by the voltage and you will get a max motor rpm. So 4s lipo=14.8v x 1000kv would be 14800kv, as an example.

Running a motor too fast will cause it to get hot, and too slow will require to much gearing (load) to reach the desired speeds. The 1515 series will easily push a truggy to 40-45mph, which appears to be the popular speed for most people. So you generally have to balance the voltage your esc can run with the motor kv to get the motor to spin at the desired rpm. Then you just gear for the speed you want.