I am wondering if any one knows the way to figure out roll out. I had this calculation on my lap top untill it crashed...

can any one help.

(Tire diameter * Pi) / final gear ratio = rollout

For example, 1/12 scale tire with 1.800" diameter, 30 pinion, 96 spur.
gear ratio = 96/30 = 3.200

(1.800 * 3.1416) / 3.200 = 1.767 rollout

For touring cars or other non-direct drive cars, factor in the 'gearbox' ratio for the specific car in with the spur/pinion gear ratio to get the final ratio.
For a car with a 'gearbox' ratio of 2.25 and the same spur/pinion as above...

(96/30) * 2.25 = 7.20 final gear ratio

Basically, rollout represents the distance traveled with one rotation of the motor
The above calculations are done in inches, but metric measurments can be substitued for the tire diameter, which will give your rollout in the same measurments.
If you do a little research on Hobbytalk, you will find rollout charts that Hank created that you can download.

thanks, I feel like a idiot b/c I looked b4 and didnt find it. I looked again and found it.
thanks again