common 4WD questions

larger tires can be bad

Ten Stupid Things
men do to mess up their 4WD

all 4WD systems on one page

4WD training

search site

To get the "crawl ratio" or "overall gear ratio" of the low range setting, 1st gear of transmission, transfer case (in 4Lo) and axle differentials are multiplied as explained before. In this example, the transfer case gear ratio was increased from 2.72:1 to 4.00:1 - the differential gears were increased from 3.73:1 to 4.56:1(mainly to make up for torque loss due to larger tires).

A well built 4WD for the more difficult off-road stuff with manual transmission should have a crawl ratio between 60:1 to 100:1 - about 70:1, like in this example, is pretty good. With automatic it should be around 50:1

Especially 4x4 with large tires should have lower crawl ratio than 4WD vehicles with stock tires.

 

Every gear ratio involved subsequently boosts the final torque output. This engine produces 200 lbs./ft. of torque - transmission and transfer case multiply it to 3064 lbs./ft. (it was 2084 lbs/ft without the lower gears) and the differentials boost it further so that each wheel receives a stunning 3493 lbs./ft. of torque (it was 2141 lbs/ft lbs./ft. without the lower gears). So, substantially lower crawl ratio for rock crawling makes much more torque available at the wheels.


By the same factor the torque increased the vehicle's crawl speed went down. Going really slow is good for more control in difficult off-road situations.

The "pumpkins" in the picture above are the axle differentials.