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Author Topic:   final drive ratio
John Bottoms
Dirt Full Roller

Total posts: 37
posted June 28, 2003 04:10 PM  
what is the formula for the final drive ratio in a car. does it include tire radious?

justin
Dirt Freak

Total posts: 263
posted June 28, 2003 05:00 PM  
Your final drive ratio is the ratio of the gear you run in your tranny multiplied by your rearend gear.

justin

John Bottoms
Dirt Full Roller

Total posts: 37
posted June 28, 2003 08:10 PM  
that is what i thought. i had someone tell me that you figured in the tires size too. that seems logical, but our definitions of final drive may be different. like i said, i thought that it was the tranny multiplied by the rear end gear, but he said different. do you know what he may be talking about?

dean_7585
Dirt Maniac

Total posts: 127
posted June 28, 2003 09:03 PM  
You use tire roll out for figuring out RPM's

racer17j
Dirt Forum Champ
Total posts: 5390
posted June 28, 2003 10:51 PM  
Yes, tire rollout or size plays a major part in your final drive. By my calculations, 1" of rollout equals 12-13 points on your final drive. That's on 1/4-3/8 mile bullrings. I'm no Einstein, so don't write this in blood. 26 points at the same track gave me 500 more rpm's. By points, I mean going from a 6.00 final drive to a 6.26 final drive. That's the same as going from a 86" tire to a 84" tire. Good luck, hope this helps!

John Bottoms
Dirt Full Roller

Total posts: 37
posted June 29, 2003 10:06 AM  
thanks to all of you for your help.

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