tkdtim

Ok guys i'm close to making a decision.
I'm sitting with 3.07 and 31" looking to go up.

Going to go with the ford 8.8 just need to decide on 3.55 or 4.10.

1.) I probobly will not go to 33" and most of my driving is as daily driver, with some logging roads & deep snow.

2.) I want to go directly to 4.10 (to have the option), but not at a great mpg loss. I currently get 19 mph hwy.

What do you think guys, will I loose much mpg going going from 3.55 to 4.10 on a 31"?

Much thanks! (and I got quoted for D30/8.25(29) for $250each, then found a pick n pull that only wants $99/axle 8.8 or anything wheel to wheel)

broncofire75

Why would you go to a 8.8 on 31s?

I loved my 3:55s and 32s believe it or not. I wouldnt run 4:10s unless it was an offroad only rig.

Oath

Why would you even re gear with 31's? I see yours is manual though. I think stock gears are fine for 31's quite honestly, maybe 3.55 would be a decent setup.

Caddy

I run, 4.10 with 35" tires and I get about 14mpg on the highway. city is a little better but not much. will be doing a full exhaust and ecu programmer as well sometime this summer.

tkdtim

I dunno what you have driven, but 3.07 gears (autos come with 3.55) on 31" tire isn't really what I call "fine".
Maybe if your ok with driving 60 mph at 1600 rpm and downshift when you cant pull a hill or when in 5th gear not really being able to accelerate until your at 70mph.

Also, the only 3.55 8.25 rear axle I found was priced at $250 and can get the 8.8 for $99.

Bonus: free disc brakes and LSD.

BudgetXJ

I'd go 4.10 if you can find one. I would think that you'd regret it down the road if you went 3.55's and then had to regear.

tkdtim

So this means I would probably get LESS than 14mpg on 31's, right?
This sounds like its heading the direction of 3.55

tkdtim

I see you have the 5 speed with 31's. Do you have the 3.07 gears still? Do you notice that 5th gear is almost useless too or are you ok with it? Maybe I'm imaging it all. I'm defiantly at least going 3.55 and trying for LSD.

BudgetXJ

Yeah, I unfortunately still have the 3.07's. I'm ok with it the way it is. Not happy but ok I guess. I still use 5th on the flats but the slightest bit of incline (or even just too much headwind for that matter) and I'm back down to 4th. I really want better gears for off road. Even in 4 low it doesn't crawl as slow as I'd like it to.

The reason I said earlier that I'd go for the 4.10's if it were me is because of the added off-road control that the lower gears would give you and having that 5th gear should make it not too bad on mpg's as well.

According to this chart, the difference is only around 300 rpm's anyways.

http://jeephorizons.com/tech/rpmchart.html

tkdtim

Awesome chart, thanks man!
I was actually trying to build a chart like that today at work to figure it out lol !

XJSETH

i wouldnt waste your money on 3.55s im on 32s and 3.55s and yeah i stuggle on the highway up hills but i manage. wait till you go bigger and regear to 4.10s.

tcountry

I have the 5-speed with 33's and 4.10 gears and when I'm on the highway going 60 the rpms are a little over 3000

mobilecherokee4

i had an automatic with 3:55, it was a little sluggish but not too much, since you have a stick i would go with the 4:10, it wont hurt your mileage, it will help it with you puttin bigger tires on it

BuckB91XJ

I would not spend the money to re-gear unless I went to the 4.10s. Automatic XJs are a dime a dozen in junkyards across the country. If you want 3.55s I would bet you could buy a set of perfectly good axles out of an XJ in a JY for less than it would cost you to buy gears and pay to have them installed.

mobilecherokee4

yeah he's right dont regear unless you go 4:10, if you want 3:55 go pull some axles, but IMO go with the 4:10