rlanda wrote:
I barely know what does "axle ratio" means, but I can't figure out why is it important.
Could you tell the convenience of this number being smaller or larger and why?
The gear ratio for the front and rear diffs(normally on a KJ) are 3.73:1,that means it take 3.73 turns of the drive shaft to make the wheels turn one full rotation,also it multiplies the turque coming from the driveshaft 3.73 times.Now gears are called low or high,low gears are numarically higher,4.10's are lower then 3.73's,and high gears are numarically lower,3.55's are higher gear ratio then 3.73's.The lower the gear ratio the more torque multiplication there is,but at the cost of high end power,say you have 3.73's and can do 130mph(it may take awhile to get there),well if you put in 4.56's you'll accelerate faster but may only get to 120mph.Higher ratio's = better MPG's(to a point) and lower ratio's are more for pulling and rock crawling.When adding bigger tires you need to put lower gears in to get back into the factory powerband,say you had 29" tires with 3.73 gears and went to 32" tires you would need 4.30 gears to be back in the factory powerband.
This chart may help with the rpms vs tire diameter-----
http://www.4lo.com/calc/geartable.htm