Gear ratio questions????

Hi everyone,
I have a few questions on gears and would REALLY appreciate your help because I keep getting different answers from other people.I have an 89 cherokee 4wd 4.0 auto with 355's in it for gears.I'm running a 3" lift kit and 30x9.5x15 BFG A/T's.I may be going to 31 inch tires soon but never any bigger.My problem is that around town my jeep is pretty fast but once I get on the highway it bogs down after 60 or so.I need to step on it or switch it to the power mode.Driving around in power mode kills my gas mileage.I get about 18mpg now.My rearend is shot in my jeep and my mechanic has an 89 4.0 5 speed with 308's in it.What would that do for performance?Would it give me higher top end or would I max out real quick.I'm not interested on doing 80mph but I would like to not have to hold the g :gee: as down so much on the highway.What would going up to 373's or 410's do,or should I stick with 355's?Please help and thanks in advance

You want lower gears (numerically higher) to increase the RPM's and give you more power, not the other way around. The bigger the tire the lower the gears you want also. If you're going with 31's then throw some 4.10's on there or stick with your 3.55's. You have to re-gear both axles at the same time and it's just not worth it to switch to 3.73's (not much difference from 3.55's). Try out the 4.10's, you should love them with an auto and 31's.

With the 3.07 you should be able to go faster on the highway but your offrpoad performance will greatly suffer. :flamemad:

Big Al 331 said:

With the 3.07 you should be able to go faster on the highway but your offrpoad performance will greatly suffer. :flamemad:

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Maybe . . . with a stiff tailwind headed down a steep hill.
You want lower gearing (which means higher numbers, like 4.10) to accommodate the taller tires, added weight, gretaer air resistance, etc.

What I meant was--higher gear/lower RPM.

laredo said:

Hi everyone,
My problem is that around town my jeep is pretty fast but once I get on the highway it bogs down after 60 or so. I need to step on it or switch it to the power mode. What would going up to 373's or 410's do,or should I stick with 355's?Please help and thanks in advance

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I go to 4.10's ... and stay at or below 65 mph with a 3+ inch lift.

I had a 3" lift and 31's for over 8 years ... decided to slow down a bit (≤55) due to the inherently poor braking power with these XJ's. Yea, I get flack from my friends ... claiming I'm getting old ... but ... you gotta remember you're competing with cars and trucks that stop on a dime these days.

I've seen more XJ's running around with crunched front ends than any other vehicle---including mine!

Don't go 3.08, you'll hate it and your engine and gas milage will too. I ran 31:10.50's for quite a while with the 4.0 and AW4. I went from 3:55's to 4:56 and loved it. With that combo I saw a jump in milage and I wasn't to the floor all the time. For me the 4:56 with 31's is the way to go with an AW4.