It depends on a lot of things, track size, speed controller, motor, motor timing etc... I'd say the best place to ask would be motor forum for the motors your running, or at the track you planning on running at. The other racers should be able to give you a good idea.
What type of surface are you running on? I had some reliability issues with my Mi1 on parking lot type tracks. The Mi1 has no space under the diffs for rock clearance, so I was going through at least a set of pulley fences per meet if I was lucky. If I was unlucky you could add a set of belts and pulleys to that as well.
If your on carpet, your all set.
