Can anyone help with that

Tire size x pinion divided by spur gear. To get tire size, you can either measure the circumference with a thin tape measure,(around the tire)or most racers use calipers to measure the diameter and multiply that by pi (3.14)

so its tire size x pinion divided by spur x 3.14 it doesnt match my chart when i tried it

You can get a Rollout chart here http://www.hobbytalk.com/bbs1/showthread.php?t=127748

and a rollout (and other stuff) program here http://www.hobbytalk.com/bbs1/showthread.php?t=127499

so its tire size x pinion divided by spur x 3.14 it doesnt match my chart when i tried it

Tire x 3.14 x pinion divided by spur.

Later, Bret

Tire x 3.14 x pinion divided by spur.

Later, Bret

I aggree with bret this is the easy way to rember it!!

Brandon

or go here and download your own roll out calculator http://www.rochesterrc.com/software/software.php?aid=2067

Pin * TireDiameter * 3.14159 / Spur = RO

RO * Spur / 3.14159 / TireDiameter = Pin

thanks 4 the help!

You can also get a rollout chart at www.gearchart.com , if you choose the "target rollout" option it will give you one chart with the pinion changes you need as your tire diameter decreases to keep the same rollout.