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Transmission & Gear Definitions Page

Gear “Ratio” explanation

If you have never understood what is meant by “4.11 axle” or “4 to one” gears for a transfer case, or a “6.32 1st gear in a transmission, I will attempt to shed some light on this: “ 4.11 ratio” means 4.11 turns of the pinion gear give one turn of the ring gear. “4 to one” transfer case gears mean the for every 4 turns of the transmission output shaft, the driveshaft will turn one time. In “4 to one” the word “to” means exactly the same thing as the colon (“:”) in  “4:1”. 

Axle ratio

Numerically higher gear ratio, meaning it will require more revolutions of the driveshaft to make one revolution of the tire. A 4.10 axle, for example will require 4.10 turns of the driveshaft to achieve 1 full rotation of the tires).

Crawl Ratio

The “crawl ratio” tells the number of times the engine turns over compared to the axles. A  crawl ratio of 20 means for every 20 revolutions of the engine, you get one revolution of the tires. A  crawl ratio of 100 means for every 100 revolutions of the engine, you get one revolution of the tires.  The crawl ratio is calculated in the lowest gear combination the vehicle has. The math consists of multiplying  all of the gear ratios in the chain together. Example: Tranny has a 6.32 1st gear. Tcase has a 2.72 low range. The axle ratio is 4.56:1. The math is thus:  6.32 x 2.72 x 4.56 = 78.39 crawl ratio. If you add a 4 to one auxiliary gearbox (such as a dual Tcase or extreme underdrive) to this drivetrain, the math becomes: :  6.32 x 2.72 x 4 x 4.56 = 313.55 to one crawl ratio.

 

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