Figuring final gear ratio on an IH puller September 04, 2010 05:25AM
Does anyone know of a formula for figuring out the final gear ratio? I have all information, such as all trans gear counts, constant mesh, ring & pinion, bull gear & bull pinion, and tire circumference.....is there a somewhat simple formula for figuring the final ratio? Any help would be greatly appreciated!!
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Re: Figuring final gear ratio on an IH puller September 05, 2010 04:19AM
To figure the final gear ratio, you need to multiply the tooth count on all the driven gears and then divide this by the tooth count of all the drive gears. The tire size is not used in figuring the gear ratio but it would affect how fast the tractor goes down the track. A gear ratio such as 20:1 would mean the engine turns 20 times to 1 turn of the tires.

If you wanted to know the ground speed, you would need your final gear ratio, your engine rpm and the circumference of your tires.
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Re: Figuring final gear ratio on an IH puller September 06, 2010 01:49AM
the ring and pinion is counted also, right ?????
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Re: Figuring final gear ratio on an IH puller September 06, 2010 02:11AM
Yes all the gear pairs in the transmission that are being used for the gear that you are running and the bull gear/bull pinion and the ring and pinion are counted. The drive gear in each pair would be a gear that is powered first and a driven gear gear is one that is being driven by the drive gear. I am not real familiar with an IH but I believe the constant mesh gears are the first to recieve power from the engine. If that is the case this would be the first pair of gears and the one that is coupled to the input shaft would be the drive gear in the first pair of gears. You just have to go through the transmission and see which gear is driving and which is being driven. In the ring and pinion, the pinion is the drive gear and the ring is the driven gear. With the bull gears, the pull pinion is the drive gear and the bull gear is the driven gear. Just take all the driven gears in both the transmission and rearend and multiply them and then divide this by the tooth count of each drive gear.



Edited 1 time(s). Last edit at 09/06/2010 02:15AM by J&R Machine.
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Re: Figuring final gear ratio on an IH puller September 06, 2010 12:35AM
Your ground speed going down the track with a given final gear ratio and engine rpm would be figured using this formula. This is if the the tires were hooked up and not allowing for any wheel slippage.


MPH = engine rpm / final gear ratio x tire circumference (in inches) x .0009469


Just for example lets assume the engine is turning 3000 rpm with a 20:1 gear ratio and tires that have a circumference of 200 inches.

3000 / 20 x 200 x .0009469 = 28.407 MPH

Just remember that for this formula, you have to have tire circumference (measured all the way around the tire) not tire diameter and it has to be in inches (not feet).
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