Originally Posted by
UN4RACING
What size rotor comes stock in the 10.5 and 8.5 sonic motors. ?
It depends which batch of motors, some of the early one's came with 12.5x25.0 with 7.25 shaft, SPEC type rotor. We requested they be changed to the 12.5x25.0 with 5.0 shaft, mod style, which they have. So you will need to check which type shaft is in the motor to know for sure. The bigger shaft costs some torque. Those seem to run good in 2wd but could hurt if your trying to run it in a SC truck.