its because of the entire left (looking at the back of the truck) casing where it covers some of the motor.. a 2200 will not fit under without an flm transmission case as stated above or major modification
You are pretty limited to 36mm diameter motors... if you have the cash look into the 14 series neu which is has the same internals as the 15xx, but in a smaller can.
2200 is wayy too much for a rustler on any voltage, a medusa 60 would move it just as well and be less weight.
Benjamin White
R/c Monster Team Driver
Jq the car, LST, Sportweks turmoil pro
Unconventional Techniques, Superior Results