Minnesh,
The most important thing you can do is change only 1 thing at a time. Go down/up a tooth on your spur....go down/up a tooth on your pinion, loosen/tighten your diffs.....the reason I say this is, if you change more than one thing at a time without running it, you'll never know what the change did. Every peice of info you have gotten on here has been good...just don't do them all at the same time. If you get too far out of shape, return the car to factory settings and start over. I still run this car in brushless stock class and I still have not been beaten because of my car......my driving on the other hand is a different story!
