25.5 , this i's where the manufacturer's would have to come in. I have not seen a ready to run with anything less than a 13.5. Most people (kids and adults ) that I've seen lately join the hobby have done so with a ready to run and to tell them they have to buy a new motor (and probably a esc too, cause the stock one is probably sensorless) right off the bat kind of ruins it and chase's them away before they even start.