Gearing – Proper gearing is the first and foremost thing to have when trying to get the most out of your stock motor. Being over-geared may give you more top end but your car may be lacking acceleration. If you are driving on a track with lots of turns and a short straight, gearing down a tooth or two will most likely yield some faster laps for you. Big straight? Long sweeping corners? Gear it up!
Motor Timing – Also known as mechanical timing. If your motor has adjustable timing, this is a great way to get some more speed out of it. The more you advance your timing is the higher the RPM it will put out but will sacrifice some bottom end in doing so. Adjust in small increments. If you are very familiar with your motor and gearing you can try to add a lot of timing (5-10degrees) and gear down a bit. This will make your motor run faster overall. Some motors like it, some don’t. You will get a different “feel.”
Tires – Tires are usually overlooked when it comes to going faster. Obviously traction is good. It makes your car controllable. Too much traction will slow your car down though. Traction is friction and the more friction you have, the more drag there is on your car. When is comes to off-road, a smaller pin or bar type tire will be faster as long as they are drive-able on the track. A skinnier tire or rounder profile tire can also be a little faster because of the smaller footprint (remember, less drag).
ESC – BOOST! Electronic timing advance speed controls are the latest and greatest in the hobby. They can make these rather mundane motors feel more like snarling beasts. When adding boost to your stock motor, the most important thing to do is gear down. Let me repeat that, gear down! Depending on how much boost you add, you will have to gear down 3-8 teeth (48pitch). The more aggressive the timing, the lower you will want to gear. The biggest mistake I see is people changing their speed control and not re-gearing. Your car will be much faster but your motor is going to go into nuclear meltdown. If you have turned up the mechanical timing on your motor, turn that back down when boosting. You will want to take advantage of the low end torque with less mechanical timing. The ESC will take care of all the top end timing your motor can handle.