Hey guys, I am looking for a formula to calculate my Final drive and roll out.

I am running a Custom Works Electric Sprint with a 1:1 direct drive trans.
how do i figure the final drive and roll out for this?

also i am running a B4 (super stock class) chassis with the 2.6:1 trans
How do i figure the final drive and roll out for this one too.

I have been searching on roll out but nothing seems to take in consideration of a 2.6:1 trans..
need some clarification guys!!
thanks

Final drive for a 1:1 car is easy. Spur divided by pinion. So if you have an 80 spur and 20 pinion, your final drive is 4.

With a transmission, it's the same but with one more step. Spur divided by pinion times trans ratio. So an 80 divided by 20 is 4 times 2.6 gives a final drive of 10.4.

For rollout, read this or just use a calculator like gearchart.com

http://www.motortuningsecrets.com/rollout.html

The formula is (pi) 3.14 x tire size x pinion / spur = rollout

Gear ratio. The higher the ratio the slower you go.
Rollout. The higher the rollout the faster you go.

With a touring car you have to include the gear box ratio in rollout

I seldom used the gear box in the formula when I ran touring unless I was converting rollout of a fellow racer with a different gear box ratio.

Rollout is especially helpful when changing tire sizes, or running foam tires. Foams get smaller each run & adjusting your rollout with the pinion to keep the desired final ratio or to adjust for more or less speed, or motor temp.

I have a widget on my computer a friend gave me years ago that I type in the ratios & it figures it.

Hope this helps
Tom

Attached is a simple Excel spreadsheet file that will calculate gear ratio, final drive ratio, rollout, etc. If you wish to input the internal gear ratio it can make the calculations, or your can enter the number of teeth for the rear diff and the center pulley (leave the “Int. Ratio” field blank or “0”) and it will perform the calculation based on this input. If you put in a number for the “Int. Ratio” it will use this number and ignore rear diff and center pulley numbers.

Supply input ONLY in the yellow shaded areas.

If you input “Tire Diameter” in millimeters (mm), than the rollout will be in millimeters (mm).

If you input “Tire Diameter” in inches (in) (decimal format only), than the rollout will be in inches (in).

If you wish to make the table bigger, just copy the bottom row down as many times as you want.

Is there any formula to estimate / calculate the speed ?
(Based on FD/Rollout and tire diameter)

Motor RPM x (Roll out in mm / 1,000,000) x 60 = Speed in KPH
Motor RPM x (Roll out in inches / 63,360) x 60 = Speed in MPH

@Calvin

Thanks for the formula

Awesome guys! thanks for the help!