Calculating final drive ratio

[Dirtracer14x]

How is final drive ratio calculated and how does it correlate to RPM? Is it rear gear ratio divided by transmission ratio (EG rear gear is 6:50, Trans is 1:1 in high gear, so final is 6:50)? Assuming that traction is constant, which we all know its not, especially on dirt would that not give you a peak RPM of 6,500? Or does something else factor into target RPM at the end of the straights?

[1cln_sdime]

tire size and how long the straight is not sure how to figure it but u can trun alot more then 6500 with a 650 gear

[mcveyracing]

maybe this will help:

http://www.race-cars.net/calculators/rpm_calculator.html

[Dirtracer14x]

That works perfectly, thanks a million!

[lucknoluck]

Here is the formula if you want it
Max rpm’s / 60/gear x circumference of tire in inches / 12 /1.466 = MPH