Originally Posted by lyons238

i was wondering this as well, I'm not sure if the internal gear ratio changed enough to go 4T bigger on the spur. I use 21 / 81 with a 6.5t motor in the 17 car with the 3 gear and it seems to be a good gearing ratio, I feel like going up to 84T with the 21T pinion would make it too snappy down low and slow top speed.

However, I have had great success with the 3 gear over the 4 gear on med-high bite clay. the car brakes better and carries way more speed in the corners.

I did get the brass Exotek RF hanger and the beefy Exotek RR hanger to add some weight to the rear of the car - that helped a bit.