Keep in mind , these
ARE NOT a serious RC car. Ok for a bit of fun, that it.
Yeah, ive run 9T & 5T in mine. The gears etc can cope....
The big problem is cornering. this car car do it at those speeds.
So a 9T, 5T or 4T is great in a straight line, the car was NEVER intended for those speeds. Its hopeless for fast cornering
The dogbones with the white plastic on the end are quite weak. get the newer tamiya solid dogbones.
Speed gear set is worthwhile as well.
But, the car is completely obselete. dont waste too many $$$ on it.
You can also put the baja arms on it (from a TL-01b) to make it wider. It helps to stop it rolling.
heres one of mine, before I broke it. Its a chop job that I built for a fun project. Ive broken 4 chassis so far, but they are cheap . :-)