Gear Ratio
Thread Starter
|
Senior User
Joined: Dec 2010
Posts: 407
Likes: 0
From: Galvin, WA
Gear Ratio
Im having a hard time finding a formula or a calculator. i think i need 4.10 gears but im not possitive. im putting a 4 inch lift on with 35 inch tires. Any help would be great! thank you!
Post Fiend
Joined: Dec 2007
Posts: 8,521
Likes: 16
From: Lost
(speed) x (final drive ratio) x 336 / tire diameter = RPM.
That formula will give the RPM at any speed, with any ratio and tire size. When you are figuring the final drive, multiply the axle ratio X the ratio of the top gear. With a non-OD trans, top gear will be 1:1 (direct), while an OD trans will have a lower than 1:1 ratio (IE: .76:1).
Also, remember that as tire diameter goes up, you'll need a little higher "target" RPM. Example, going from a 33" tire to a 35" tire, ideally you would want to have 200-300 more RPM to overcome the higher rolling resistance of the taller tires.
That formula will give the RPM at any speed, with any ratio and tire size. When you are figuring the final drive, multiply the axle ratio X the ratio of the top gear. With a non-OD trans, top gear will be 1:1 (direct), while an OD trans will have a lower than 1:1 ratio (IE: .76:1).
Also, remember that as tire diameter goes up, you'll need a little higher "target" RPM. Example, going from a 33" tire to a 35" tire, ideally you would want to have 200-300 more RPM to overcome the higher rolling resistance of the taller tires.
Elder User
Joined: Apr 2009
Posts: 922
Likes: 1
From: San Diego
The super easy to use search function of this forum says:
https://www.ford-trucks.com/forums/9...ml#post8830072
https://www.ford-trucks.com/forums/1...l#post10112981
Here is where someone says the calculator is:
https://www.ford-trucks.com/forums/7...ml#post6756082
Another linked one in the same thread:
Novak Conversions - Gearing & Gearing Math for Jeeps
And one that does the math for you:
Automotive Calculators offer to you by Ford Trucks Enthusiasts | www.ford-trucks.com
On a side note, Rogue, I am starting to admire your patience.
simple search revealed that you have answered this question multiple times, even twice today...
https://www.ford-trucks.com/forums/9...ml#post8830072
https://www.ford-trucks.com/forums/1...l#post10112981
Here is where someone says the calculator is:
https://www.ford-trucks.com/forums/7...ml#post6756082
Another linked one in the same thread:
Novak Conversions - Gearing & Gearing Math for Jeeps
And one that does the math for you:
Automotive Calculators offer to you by Ford Trucks Enthusiasts | www.ford-trucks.com
On a side note, Rogue, I am starting to admire your patience.
simple search revealed that you have answered this question multiple times, even twice today...
