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Gear Ratio Question

961 views 12 replies 11 participants last post by  The Black Sheep 
#1 ·
What do yall think the best gear ratio would be for a TJ with 36's and a front Dana 30 and rear Chrysler 9.25?

I need some decent gas mileage with some punch on the trail too.

I hardly ever drive on the highway.

I was thinking 4.56?
 
#4 ·
x2

But if you hardly ever cruise on the highway, it doesn't matter what trans you have. I vote for whatever's the deepest you can go with that set, probably 4.88s. 5.13s or 5.38s would be ideal. Not much you can do for gas mileage for a TJs on 36s around town, all you can do is drop the gearing as low as possible to help keep the engine up in the powerband as much as possible.
 
#8 ·
My sister has a YJ on 36's, has a 4.0 backed with a NV3550, and a NV231. She still runs the stock front axle (Dana 30, open) and a Comanche 44 (locked) out back, with chromo shafts at all corners. She went with the recommended 4.88 gearing, and it seems to hold up decent so far. My only complaint after all the work is the damn bias ply tires.... but thats for another day...
 
#10 ·
4.88's(lowest you can go)

. . . and 36's and "decent gas mileage" don't live together. Go buy a econo box to get around and to work and back and use the jeep sparingly and off roading only. Thats what I do.
 
#13 ·
I wouldn't touch anything past a 4:56 for the D30. Ive seen ALOT of 4:88 pinions go with little abuse, even one or two 4.56 gear sets. Its one thing to help offset the power loss from throwing on bigger tires, but its another thing to totally negate it using gears. A lifted jeep on 36"s will never be a beacon of fuel economy and it will eat a little horsepower, no matter what gears you stick in it. Anything yoiu add to the bottom end, you lose from the top end gear wise. I have 37"s 4.10s and a 4 speed and 65-70 mph is about all it can do in a cruising gear range for comparison.

Check out Grimm's ratio calcs for top speed etc at certain RPMs and gear sets, based on tranny/t-case combo you have, also figures in tire size and give you hypothetical speed,RPM, and crawl ratio numbers. Its a great page!!.

http://www.grimmjeeper.com/gears.html
 
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