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Please Settle This: Gear Ratio For 31's

98stocker said:
3.55 and 31's are fine for me as the engine is plenty torquey.
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x2_poster.jpg
 
i wouldnt even worry about wasteing your money on gears for 31" tires if you have 4.o motor you will not realy even notice it at all i have ran 3:55's for a long time with 33" tires i would spend money on a gear set for your transfercase.
M4Madness said:
First, I've read the tacked FAQ and read through 34 pages of topics that came up when I searched for "gear".

I have a 1996 Cherokee Sport. It has a 4.0L engine, an automatic OD transmission, and 3.55 gears. I'm wanting to lift it and install 31's. It is my daily driver, with most driving at highway speed. From my calculations, to get back to the stock gear ratio after adding the bigger tires, I'll need 4.11's.

Some say that I'll be happy with 4.11's, while others say to definitely go with 4.56's. I'm leaning towards the 4.56's, but want to be sure that I won't be disappointed -- some say that this is too low-geared for 31's.

Hopefully this can put the argument to rest, and future newbies will benefit from the input. Thanks.
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mud4x4lover said:
i wouldnt even worry about wasteing your money on gears for 31" tires if you have 4.o motor you will not realy even notice it at all i have ran 3:55's for a long time with 33" tires i would spend money on a gear set for your transfercase.
Click to expand...

The dood lives in Indiana and what, exactly would a gearset for the transfer case supposed to do for him???

For short money in similar use, I'd pick up a front 30 with 4.10 out of a 4cyl 92+ XJ, use whichever brakes/ hubs/steering are in better shape on the donor, and keep the other junk for spares.

I am not clear if you have a D35 rear or a 8.25" (or if they put 4.10s in the 8.25s) but either find a 4.10 swapper or regear the back. You would not need a new carrier for either of those axles... just ring & pinion gears, install kit and a gallon of oil.

Me personally, I've done 4.56 & 31" (4.0 AW4) and loved it. No probs at 75-80 on I-40. I have 4.56 waiting to go in my current ride... but at one point had 4.10s and decided not for me (hilly backroads mostly) Also consider that those 'XX" tires' are probably a lesser working radius, so "do the math" with that in mind.

regearing (opposed to swapping in ready-set axles) is kinda expensive... even if doing it at home. Not something to do often IMHO.
 
Well, here's what I've decided so far. I'll probably go with a Rubicon Express 3.5" Super-Ride kit, a Tom Wood slip yoke eliminator kit, a set of 31" BF Goodrich Radial T/A KO tires, and regear at a later date with at least a locker in the rear. I'd like at the very least to be geared back like I was before the larger tires, which means a set of 4.11's. In the mean time, I can just drive around in 3rd to keep the RPMs up. What do you guys think of the factory paint? :puke: I bought this Jeep 3 years ago after driving 75 miles one way to check it out. The photo of it in the magazine was black and white, so I had no idea that it was magenta. I sucked it up and bought it anyway since it was a well-maintained one-owner. I've since put 40,000 miles on it, with a water pump and routine oil changes being the only maintenance needed.

459635.jpg
 
Personally...
I'd put a lift on it...If I had vibes get a SYE...if not save your cash.

I'd put the tires on it... if its a dog, regear it...if its ok with you...leave it alone and save some cash.


I have about 4 inches of lift and 31's.....I don't need a SYE and I still have my 3:55's...they are fine.

In other words don't fix it if it aint broken.
 
cdhowell said:
Stop and think that the charts are based on 1:1 ratio's in a manuel tranny. and the 31's will be a little wider increasing rolling resistance. The taller stance will increase wind resistance. Milage will drop slightly even if you regear. I say do a budget boost and get a set of trail tires for your hunting trips. a used set will cost half of what regearing will.
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Nope the 5-speed has an overdrive ratio of 0.79. But good point that top gear in the AX4/5, AW4 pre 1991, and AW4 post 1991 are all slightly different. They range from .70 to .79 final ratio which is the same percentage as 4.11 to 4.56.

(Happily running 32s, 4.11 junkyard axles, and an AW4 with .75 OD)
 
I have a manual 98 xj that came with 3.07s. I put a 3 inch lift on it and swapped in 3.55 axles for like $200 the same time I put 31's on. It was faster and torquier than stock, but if you do the math I was lower than stock. Now I rn 32's on 4 inches of lift, and am currently mathmatically the same as stock with the 3.55s. Im getting an average of 16.5-17 mpg in the city, and 20-22 on the highway doing 70-75. My engine is all stock. I did lose a substantial amount of power going from 31s to 32s, I plan on doing some engine mods to get the power back, but for now its fine.
-Jerry
 
ok i never said spend the money on a gear set i said leave it alone! and if he is going to waste the money it should go in the transfercase not the axles!
jeep2.jpg
jeep3.jpg
33's locked custom hysteer revolers 4:1 t-case slip yoke elim.
jeep4.jpg
woody said:
The dood lives in Indiana and what, exactly would a gearset for the transfer case supposed to do for him???

For short money in similar use, I'd pick up a front 30 with 4.10 out of a 4cyl 92+ XJ, use whichever brakes/ hubs/steering are in better shape on the donor, and keep the other junk for spares.

I am not clear if you have a D35 rear or a 8.25" (or if they put 4.10s in the 8.25s) but either find a 4.10 swapper or regear the back. You would not need a new carrier for either of those axles... just ring & pinion gears, install kit and a gallon of oil.

Me personally, I've done 4.56 & 31" (4.0 AW4) and loved it. No probs at 75-80 on I-40. I have 4.56 waiting to go in my current ride... but at one point had 4.10s and decided not for me (hilly backroads mostly) Also consider that those 'XX" tires' are probably a lesser working radius, so "do the math" with that in mind.

regearing (opposed to swapping in ready-set axles) is kinda expensive... even if doing it at home. Not something to do often IMHO.
Click to expand...
 
I have a 96 Cherokee 4.0 with 4.56 gears with 31's, I get 15 mpg on the highway.

I have a 89 Cherokee 4.0 Renix with 3.55 gears with 29's, I get 22 mpg on the highway.

From my experience I would prefer 33's on the 4.56's than the 31's.
 
for any one who's looks at this thread there is a thread in the FAQ section that has an algebraic equation that explains what gearing you need to return your rig to stock power.

27/31 = 3.55/new gear ratio

Cross multiplying (thought you'd never use algebra again?) gets you this:
31 X 3.55 = 27 X new gear ratio

110.05 = 27 X new gear ratio

110.05/27 = 4.0759

closest to that is 4.10. If you want to go lower go lower. if you just want stock 4.10 is fine.
 
barillms said:
You can run any gear ratio with 31s!! They're 31s, practically stock! Who cares. Maybe not 3.07s, but 3.54s, 3.73s are FINE FINE FINE!

4.56s w/ 31s, are you kidding me! What a waste of time and money!
Leave your gearing stock with 31s, literally 2.5 inches taller than stock tires!!
People think too much about these Jeep ideal perfection figures.
235s - 30s - 31s - 32s - 33s - 34s - 35s
stock stk stk 4.10 4.10 4.10 4.56
4.56
Click to expand...

Buddy, you live in Ohio - when was the last time you tried dragging your jeep from 4000 ft to 8000 in about ten miles? Altitude & hills make gears a little more relevant...

to the OP: If you are in the city most of your driving, as you indicated, 4.56 is going to make it a lot of fun to drive. If / When you go up a tire size, you'll be glad you are already at 4.56
 
If you will never go offroad and never go taller that 31" tires - go with 4.10s. If you will go offroad and will even consider going taller that 31" tires - go with 4.56s.
 
I guess no one noticed this thread is/was 2 years old
 
No need to touch gears for 3.55s.

Just downshift to 3 for hills.

BTW, I ran that combo for over a year on my tranny with fluid that looked like motor oil.

At 270k now and still going strong,
 
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