Pictured above are the gears in the rear end of a car.
What you do:
Choose a gear ratio that gives you the traction, acceleration and top speed you want.
Factors to consider:
The HiPerMath equation is:
miles per hour =                           rpm x tire diameter
transmission gear ratio x rear end gear ratio x 336
Try out the gearing on the track to see what your car will do.
mph = miles per hour
rpm = revolutions per minute