I'm used to running on asphault with rubber tires so rollout is not a factor. Now I'm racing on carpet and need to calculate rollout. I checked all the other rollout threads and they just give the websites to get charts. I don't need charts. Any person can punch numbers into a program to come up with a chart. I want to know the mathmatical formula to come up with those numbers. I am also looking for an average rollout for a tuned stock motor on a small technical track. BTW I use mm in measuring the tire diameter.

Originally posted by Smalls Tire size times PIE (3.14) divided by spur times pinion.
Ie. 1.74*3.14=5.4636 / 98 = .05576 (rounded) * 38 = roll out of 2.11

Thanks newracer. I was wondering why the formula that was previously mentioned was also on a 1/12th forum and the numbers I was coming up with didn't seem right.

E.J.- I was looking for the accual formula to calculate rollout so I would have the knowledge to make changes to compensate for a change. Not to have a bunch of charts that mean squat.

Originally posted by NismoSkyline17 I'm used to running on asphault with rubber tires so rollout is not a factor. Now I'm racing on carpet and need to calculate rollout. I checked all the other rollout threads and they just give the websites to get charts. I don't need charts. Any person can punch numbers into a program to come up with a chart. I want to know the mathmatical formula to come up with those numbers. I am also looking for an average rollout for a tuned stock motor on a small technical track. BTW I use mm in measuring the tire diameter.

Thanks in advance.

I gave you the 12th scale roll out. You never said it was for TC ( although I assumed it when I saw rubber tires ), but you never said what it was for and what your drive ratio was...

Originally posted by NismoSkyline17 Thanks newracer. I was wondering why the formula that was previously mentioned was also on a 1/12th forum and the numbers I was coming up with didn't seem right.

E.J.- I was looking for the accual formula to calculate rollout so I would have the knowledge to make changes to compensate for a change. Not to have a bunch of charts that mean squat.

You only need one chart, (for each type of car) as your foams wear down, it will tell you what pinion to use.