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Calculate Final Drive Ratio
Calculate Final Drive Ratio. If the motorcycle being modified will be ridden on the street, it is important to get the speedometer recalibrated following any change in final drive ratio. For this example we will say the axel ratio is 5:1.

Use our gear ratio calculator to find the effective gear ratio your vehicle will have with a new tire size. Select transfer case from the drop down list or, if it's not in the list and you know the gear ratios of your transfer case, enter them below. We need to multiply this number with the transmission ratio.
(1) The Pinion Gear, And.
If you know your gear ratio and tire size you can get a fairly close idea here. Gear ratios are typically expressed in z:1 (2.055:1 for example). For example, one of my cars has a 36t diff pulley and a 16t center pulley.
Although I Was Really Only Concerned About My Transmission I Figured I Might As Well Calculate All Four Possible Final Drive Ratios For The Benefit Of Others.
I finally selected the 5th gear. I should get a gear ratio of 2.25:1. Final drive ratio understanding final drive ratio.
Generic Final Drive Ratio Graph.
(rpm x tire diameter inches) / (final drive ratio x transmission gear ratio x 336) = actual numerical gear ratio to the ground from every revolution of the engine. Gearbox (1 st) gear ratio, i x = 4.171; We need to multiply this number with the transmission ratio.
There Is Nothing Mathematically Complex About Calculating A Gear Ratio, The Hard Part Is Determining The Different Variables.
It originally came with 3:73 gears and 245 75r 16 tires and i want to find out what the final drive ratio was before i installed the 285 75r 16's goodyears that i now have on it. If you alter this ratio, it also changes every gear’s effective ratio, affecting the vehicle’s performance and economy. For this example and most cases this is 1:1 on the high end.
36 / 16 = 2.25.
For the sake of simplicity, we’ll use z above to get the car’s final drive ratio. Fd (final drive/diff ratio) x wheel rev per mile. If your tires are bigger than stock you probably, like myself, have spend a lot of time trying to wag (wild ass guess) your actual mph when going down the road.
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