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  #1  
Old July 26th, 2013, 10:21
escout's Avatar
escout escout is offline
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Best Gears For 31" Tires???

So, I've recently looked through a bunch of gear vs tire size charts (as well as done the math myself) to decide what would be a good choice for ring and pinion in my XJ. Based on the setup I want to run, 3.90 gears seem like the best option, but it's no secret that they don't exist as an option for the Cherokee (at least I've not been able to find them). If anyone is running 3.90's, I would like to know. I live at 7200' elevation and stock gears won't cut it, especially in the mountains.

This is my DD and I need it to get reasonably good mileage. I frequently run 70mph and drive quite a bit of in-town too. If 3.90's don't exist, what's my next best option? 3.73's?? or 4.10's?? Any recommendations for good gear brands for these axles?


Additional Info:
2000 Jeep XJ, 4.0l, AW4, np231j
3" RC Lift and 31" Tires
(d30 low-pinion, standard-cut, 27-spline, 3.55) FRONT AXLE
(Chrysler 8.25, 29 spline, 3.55) REAR AXLE

Thanks!!
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  #2  
Old July 26th, 2013, 10:31
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WAZZUXJ WAZZUXJ is offline
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Re: Best Gears For 31" Tires???

4.10's if you never plan to go bigger than 31's. If you think you will someday bump up to 32-33's then go 4.56's.
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  #3  
Old July 26th, 2013, 10:33
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Outlander560 Outlander560 is offline
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Re: Best Gears For 31" Tires???

4.10s
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  #4  
Old July 26th, 2013, 10:40
djlarroc djlarroc is offline
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Re: Best Gears For 31" Tires???

i did 4:10s and am running 245/75 (about 31").. wish i had run 4:56. Climbing hills, it would be welcome, and I don't normally drive my jeep over 75 anyway. I'm getting an avg of 16.5 mpg city/hwy. i have a 4.0 auto 200k.
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  #5  
Old July 26th, 2013, 11:08
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OutkastBoss OutkastBoss is offline
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Re: Best Gears For 31" Tires???

4.10

I got 4.56 for my intended 33's I never bought yet.

I have been Daily driving 4.56 on 31's for over a year and its okay but too low imho .
I don't ever go over 5mph over , if I was a speeder It would bother me on the highway .
Of course on the low end its a blast to drive and jumps right out into traffic and gets up to speed which is helpful in STL .

Off road I haven't used 4Lo In a long time , even playing in the rocks at Winterfest so it pulls hard .

33's coming soon , or so i tell myself .

Last edited by OutkastBoss; July 26th, 2013 at 11:23.
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  #6  
Old July 26th, 2013, 12:14
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Johnnie Walker Johnnie Walker is offline
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Re: Best Gears For 31" Tires???

4.10's min. , if you can find a 4cyl XJ, most likely will have a pair of axles that are 4.10s some rare ones have 4.56 with autos. I have personally NEVER seen a 4 cyl. auto.
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  #7  
Old July 26th, 2013, 12:26
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blondejoncherokee blondejoncherokee is offline
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Re: Best Gears For 31" Tires???

leave em stock and dont waste money on 4.10s if you are planning on 31s. once you go from 31s to 33s/35s then just go 4.56 or 4.88.

just saw you live in the mountains. I ran auto/4.88s/31s for like 6 months at one point. it was totally doable. I say 4.88 regardless in case you ever go to 33s or bigger.
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  #8  
Old July 26th, 2013, 12:33
WB9YZU WB9YZU is offline
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Re: Best Gears For 31" Tires???

Yup, a set of 4.10s would be outstanding and not too bad on the gas.
Look under newer 4 cylinders with 8.25's.
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  #9  
Old July 26th, 2013, 14:04
Devilfrog Devilfrog is offline
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Re: Best Gears For 31" Tires???

You really want the 4.0 to sit at 2000rpm range at cuise for best mileage. 3.73 form grands or newer TJ's or 4.10's feom a 4cyl would be my choice for a 31 inch tire. I'm going to toss a grands rear my MJ when I find one.
4.56 would have the motor screaming on the highway, and actually decrease mileage.

My XJ runs 33's and 4.56 and I'm still rolling in the 20-22mpg range on the highway. Town is lower at about 17mpg average. Highway cruise rpm is 2000-2500 from 55-65 mph (80-100km/h)
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  #10  
Old July 26th, 2013, 16:06
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blondejoncherokee blondejoncherokee is offline
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Re: Best Gears For 31" Tires???

Ya I missed the good mileage part. I just feel like in a year or two of wheeling, and youll be on 33s or 35s and youll wish you had gone deeper
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As soon as I crest the top i'ma turn driver and floor it!

1998 4.6 stroker , aw4 XJ on 60/14b , 5.38s, grizzly/detroit, cage, 40s, psc big bore box , assist, 3 link,transgo aw4 reprogram
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  #11  
Old July 26th, 2013, 16:50
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escout escout is offline
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Re: Best Gears For 31" Tires???

Cool, sounds like 4.10's might be the way to go. Does anyone have good experiences with a certain brand of R&P?

Quote:
Originally Posted by blondejoncherokee View Post
Ya I missed the good mileage part. I just feel like in a year or two of wheeling, and youll be on 33s or 35s and youll wish you had gone deeper
Lol yeah, I totally understand that. I've already got the disease when it comes to going big on tires and builds.....Trying to go a little more modest on this build since I already have my dedicated crawler on 37's
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  #12  
Old July 26th, 2013, 18:23
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blondejoncherokee blondejoncherokee is offline
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Re: Best Gears For 31" Tires???

good call. ya i want to eventually get a stocker and just do like 2" BB and 31s and leave my crawler for the harder stuff and have something for everything in between...well in that case, go 4.10
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As soon as I crest the top i'ma turn driver and floor it!

1998 4.6 stroker , aw4 XJ on 60/14b , 5.38s, grizzly/detroit, cage, 40s, psc big bore box , assist, 3 link,transgo aw4 reprogram
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  #13  
Old July 27th, 2013, 06:30
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Frank Z Frank Z is offline
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Re: Best Gears For 31" Tires???

Take the guess-work out of the equation. Go to the following link and do a side by side comparison of the various gear ratios and see which get's you the closest to the stock powerband.

http://www.grimmjeeper.com/gears.html
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  #14  
Old July 27th, 2013, 10:05
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Red91Laredo Red91Laredo is offline
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Re: Best Gears For 31" Tires???

I'd go 4:10 as well... I have 31's on my XJ that I drive everywhere and sometimes it'd be nice to have lower gears. The power at lower speeds is good (3.55 gears), but on steep hills at highway speeds more gear would be really helpful. If you're definately going to stay on 31's, 4:10 gears should be about perfect.

I've thought of finding a set of 4:10 axles to swap in, but want to run 32's in the future, so I'll probably wait and regear to 4:56.
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  #15  
Old July 27th, 2013, 13:52
carves carves is offline
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Re: Best Gears For 31" Tires???

Just as a comparison /info

I've recently gone to 4.10s ... and only running 30" tyres.

Quite happy with the result ... Better driveability and negligible fuel use variation.

Last edited by carves; July 27th, 2013 at 13:56.
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