Originally Posted by
rcsuicide
Always go with a 4.0 FDR to start with. Measure your motor temp after 20 laps. If your motor temp is under 160 Fahrenheit, then you can afford to go with a larger pinion gear to get more speed. Always monitor your motor temp because if it goes over 170 Fahrenheit you will damage your motor.
That's my $0.02.
Sounds about right although the comment about gearing for more speed needs some clarification. Start with the 4.0. After you run it and check temps, change gearing based on YOUR driving style and the TRACK LAYOUT. For instance: on our tight, technical layouts I don't have the best speed on the 1 major straight BUT once I'm in the twisty sections and due to my driving style I make up alot of time therefore I won't gear my car for more top end speed,which takes away from acceleration speed. I think you'll find most people commenting that typical motor temps will be under 135 so you've got quite a bit of room to play with gearing.