JWB37

Hello all, I'm wanting to regear my XJ. Currently sitting on 31s with 3.07s. The torque at freeway speeds is just pathetic, and at the end of next summer I'll be driving from california to colorado. A lot of the speed limits are 75, and up hill. I know my Jeep can't do that with its current gearing, let alone loaded up will all my stuff. In addition to that, I'd like a slower crawl gear.

Im just wondering what kind of milage people are getting with 4.10s and 31s, and how they do on the freeway. I have an AX-15 tranny too. Currently I get about 14-15mpg around town, and 18 on the freeway. Should I go with 4.10s, or look for a set of 3.77s?

salad

3.55s is a common swap for 5-speed owners with 31s. It puts you just over stock ratio, and is really easy to find thanks to all the automatic owners regearing. At 4.10 you'd be turning your engine pretty fast on the freeway.

Check out this calculator: http://grimmjeeper.com/gears.html

CheapCherokee

i run 4.10s on 31s, but with my AW4. i get around 19 mpg highway 13 city

JWB37

With 31s and 4.10s based on that calculator, I would be at 2250 rpms at 65mps and 71mph at 2500 rpms. The I6 motors most efficient oporating range is within 1800-2200rpms for freeway speeds. It would be fine for city and local freeways, but cross country roads that are 75mph would be a bit challenging.

It's not ideal for the cross country trip, but it would be much better around town, and for crawling. I would just have to keep it under 70mph. The thing is, after my current tires wear out, I want to swap to 33s. If I was staying on 31s forever, I'd just find a set of 3.73s.

Bht911sc

I too just replaced my gearing to 4.10 and also run 31" tires. My mileage also jumped with the change. In overdrive it is comfortable at 70 mph.

ThatAintStock00

I ran almost that with my '00 AW4 with 3.55s and 235s when I first put on tires. 60mpg was 2000rpms, 75 was just under 2500. Pulled fine; but i had a serioud decrease in mileage after 70mph. Dropped from 19-20 down to 16-17; it is a brick with wheels though.....

JWB37

Thats good to hear. Honestly, as long as nobody claims to get terrible milage, I'll go with 4.10s. I would rather be geared too low, than too high. I may also tow a small trailer, so the 4.10s would probably be my best bet. I just want to hear what everyone else has to say, and how it effects milage. I'm happy with my milage now, but I'm afraid it can only get worse lol.

salad

Oh well if you're doing 33s at some poit definitely just grab 4.10:1s

BumsModified98xj

I need an mpg increase also my commute to work is 70 miles round trip, It also has 3.55s with aw4 and 31s. Would a set of 4.10s help me? I love to drive my jeep everyday and I would hate to get rid of it due to poor mpg's and rising gas prices, I just cant see myself downgrading to a little ricer. Any help and recommendations?

Potatowalker

I currently have the AW4 with stock gearing and 31s. I am planning on getting 33s when my current tires wear out and the plan is to upgrade to 4.10 gears before that happens. Anything lower would be too low on 31s and the 3.55 is a little too high on 31s for my taste and would definitely suck on 33s. I live in the mountains of Colorado and currently the jeep is a little sluggish going up big hills when loaded down. I had 32s on 3.55 gears with the AW4 for a bit and it was sloooow on hills.

If I were you, I'd do the 4.10s - especially if there is a possibility that you'll be getting bigger tires in the future. In my opinion, going over 70 in an XJ that hasn't been race-modified is silly and pointless anyway, especially when loaded down. I don't even remember the last time I did 70mph in mine; but then I do tend to avoid populated areas like highways and cities and such.

I get about 13-15mpg around town and 18ish on long drives.

muffinman

Potatowalker,are you in the San Luis valley? I to run around the rockies and 4.10s were not so good with my 34 inch swampers .Measured right at 33. Might think about 4.56.

Potatowalker

Na, I'm up in Grand County by Winter Park. Thanks for the input though, that's good to hear from someone that's had that setup in these kinda mountains. I started out thinking I wanted 4.56 then decided I wanted 4.10s cuz it does see highway miles on I70 when I go over to Moab or Denver. Sometimes I think I may only get 32s next also. I'll probably change my mind a million times before I'm at the point where I get gears anyway so I should probably quit worrying about it 'till then.

Gee oh Dee

AW4s and AX15s are completely different. They are geared different. What works with one isn't going to yield the same results. With the manual trans you don't need such numerically high gears, its just not necessary.

As for not taking an XJ past 70....thats just silly. Plenty of states have 70mph and up speed limits. If your XJ doesn't drive straight safely enough to travel at that speed, it needs work.


Now, for the original question...4.10 gears on 31s with a manual trans....

I ran that very setup for about a year. It sucked. First gear was USELESS, I had to use 2nd all the time, and my freeway RPMs were WAAAAY higher than necessary. That translates to a big decrease in highway mileage, and premature wear on the motor.

With all that said, unless you do indeed plan on getting 33s sometime in the near future, like before this road trip, then regearing to 4.10s will be a step in the wrong direction. 3.55s or 3.73s would be a better choice for you, but regearing isnt cheap, so I would think long and hard on this before pulling the trigger....

ohio95xj

THANK YOU!!!!!! I was about to post pretty much that same message. it has been sooo frustrating reading some people's posts,because they seem to to forget entirely to account for the transmission

Potatowalker

Sorry for the confusion. Having had only AW4s I wasn't aware of such differences.