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4.56 on 31's

That's what I was thinking. 4.56 for 31" tires just seems a bit too extreme. I'm also not towing hardly ever and when I am it's just a dirt bike so nothing heavy at all.
 
That's why I'm adjusting final drive with tire size
 
XJEEPER said:
Odd, my experience is the complete opposite x 10+.

And an "easy" tire size swap to compensate for the wrong gearing selection costs what?

hasta
Click to expand...

Go as high as possible that's my thought. It's not going to hurt the jeep to run 4.88 gears on 31,s and if you want bigger tires down the road you will not need to change gears again makes sense to me.
 
Around town, the 4.56 will help you more than the 4.10s.

Once I can get my driveline vibration issues sorted out, I'm going to be going 4.56 on my Cherokee. The biggest tire I plan to run is 235/85-16. As it is right now, I get better mileage in Direct than Overdrive. 3.55 gears and 215/85-16 tires.

My Cherokee isn't a highway cruiser. I have a Ford Focus for that. My Jeep gets used as a Jeep. So, generally, when I'm driving it, I am towing something or hauling something or wheeling it.
 
4.56s on 31s is what i should have run. I went 4.10s first thing when i was still bone stock because they were cheap to do and i was planning to step up to 33s (was running 235/75 at the time). the initial setup of 29s on 4.10s was my favorite by far. CA grades were a breeze and i got my best mpg of 13.5 city and 19 hwy. then 31s came and while tolerable its just not the same. Hills took a little more work but it still could cruise in OD on flat land just fine. MPG dropped slightly in the city and was about 16-17 on the freeway depending on load and how many hills i climbed.

I'm now on 33s, but i wont go into that since 31s are the topic here. With that said i would spring for 4.56 for 31s in a heart beat. the higher rpms are really not an issue for the 4.0 and if you are really loaded down you will see better mpg with the 4.56 vs. 4.10s. i really miss running 29s on 4.10s haha
 
cheapcherokee93 said:
4.56s on 31s is what i should have run. I went 4.10s first thing when i was still bone stock because they were cheap to do and i was planning to step up to 33s (was running 235/75 at the time). the initial setup of 29s on 4.10s was my favorite by far. CA grades were a breeze and i got my best mpg of 13.5 city and 19 hwy. then 31s came and while tolerable its just not the same. Hills took a little more work but it still could cruise in OD on flat land just fine. MPG dropped slightly in the city and was about 16-17 on the freeway depending on load and how many hills i climbed.

I'm now on 33s, but i wont go into that since 31s are the topic here. With that said i would spring for 4.56 for 31s in a heart beat. the higher rpms are really not an issue for the 4.0 and if you are really loaded down you will see better mpg with the 4.56 vs. 4.10s. i really miss running 29s on 4.10s haha
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Even unloaded the 4.56 will be nice in the hills!

Used to have 4.10s, NV3550 on 205-75-15 tires on a past jeep. That was fun!
 
Last edited:
To the OP, my xj (auto, 4L) spins 2600 rpm at 65 mph. That is with 31's all terrain tires and 4.56 gears. If it is important to you that you cruise on the highway at 75 mph go with the 4.10 ratio. Otherwise reap the benefits that the deeper (456) gears provide (more low end torque, better towing, better crawl offroad).
 
Rod Knee said:
To the OP, my xj (auto, 4L) spins 2600 rpm at 65 mph. That is with 31's all terrain tires and 4.56 gears. If it is important to you that you cruise on the highway at 75 mph go with the 4.10 ratio. Otherwise reap the benefits that the deeper (456) gears provide (more low end torque, better towing, better crawl offroad).
Click to expand...



what mileage do you get at that?

2600 is no problem all day
 
Just did the swamp lake trip. 2500 rpm at 65, 16mpg loaded down. I did have to drop it to third to climb grades. 285/70-17 tires 4.56 gears.
 
For a rig on 31's with an auto transmission that sees mostly hwy miles, I don't know that there is much benefit in going from the stock 3.55 ratio to the 4.10 ratio, especially when factoring in the cost of regearing. If the rig is weighted down, runs at high elevation, tows, is used offroad (etc) just go with the deeper gearing.
 
A lot of people make the mistake and think the 4.0 is only good UNDER 2K RPM. The ones I have had have always been happy between 2000 and 3000.

Now, they don't mind idling around on the trail all day and have no problem doing so. On the highway, let 'em wind. Just not at like 4000RPM - then you'll deposit lots of piston skirts in the pan.
 
so I just swapped 4:10's into my 99 4.0 auto 4 door ,
245/74r16 on rubi wheels . My jeep is a pig with bumpers, skids, tire carrier , winch , tons of gear . I only really noticed a difference over the 3:55's on long hills ( not that we have a lot of those here in MO).
I just returned from a Colorado trip and my jeep drove much better than previous trips where before above 5,000 ft. was just embarrassing .
First gear in low side was better also , I hardly used my brakes .
I was patient enough to hunt C/L for over a year to find a 4 cyl. xj to rob the axles from (that wasn't a d-35) . If I had to buy new parts though I would go with 4:56 .
 
Miller88 said:
Now, they don't mind idling around on the trail all day and have no problem doing so. On the highway, let 'em wind. Just not at like 4000RPM - then you'll deposit lots of piston skirts in the pan.
Click to expand...

What makes you think that?
 
cal said:
What makes you think that?
Click to expand...

For some reason, once you start hitting above 4000 repeatedly, they let go. The only 4.0s and 2.5s I have seen pop ( in person ) was when someone held them at the red line a bit too long.

Unless you're running like 23'' car tires, I don't think it's possible gear it low enough to be at a sustained 4000RPM on the highway haha.
 
Miller88 said:
For some reason, once you start hitting above 4000 repeatedly, they let go. The only 4.0s and 2.5s I have seen pop ( in person ) was when someone held them at the red line a bit too long.

Unless you're running like 23'' car tires, I don't think it's possible gear it low enough to be at a sustained 4000RPM on the highway haha.
Click to expand...


We've held our motor over 4,000 RPM for 4+ hours at a time. Hasn't blown yet..
 
Just an observation. Only time I've seen them pop.

I have had mine up there a few times pulling hills with a trailer. Mine didn't let go either.
 
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