how about this feature?:

Suggested Starting Roll-out:
Select Track Type (tight & Short, Moderate & Mid Length, Wide & Sweeping)
Select Motor (Power/Torque Range) - can some of the guys here with Dyno's give some guidelines? Or else get some data from somewhere. So you could select the range based on your motor's #'s.
Also maybe something about how cut the comm is - the smaller the Diameter the higher power in higher RPM's but lower torque (This is right isn't it?)

I know all the seasoned racers will tell you to "figure out" your motor's power. But a good starting point would still be very usefull.

And Rollout is the distance your tyres roll for one revolution of the motor. So Circumference (2*Pi*R) / Gear Ratio gives you rollout.