Hello Hot_Carl,

You may be better off posting this question at the "Monster Truck" section of RCU. The CEN Funfactor ATX is very similiar to the Funfactor MT & MT2. In fact, I bought an ATX & modified it to a MT2 with bigger tires & smaller pinion.

You can drop a .21 in the MT2, so I see no reason why the same cannot be done to the ATX. Several people at the "Monster Truck" section have done it. This is the 1/8th Scale Buggy section & the ATX being a 1/10th truck, people may not be as familiar about this truck.

Normanski