Are 31's worth it?

[RedChuck]

If you live in a "hilly" area you will feel it a lot more than guys in flatlands - you will barely be able to get into OD with an auto tranny. I hated 31's with 3.55s and had to regear within a week. It depends on how much power loss you can tolerate. I would plan on regearing.

i have 3.07 with 30s on right now it is not that bad i raced late 90s dodge ram the other night and out ran him. of curse i have a manual and 1st gear is 3.83 instead of the autos 2.80 but starting from second (2.33) is not bad when the clutch is feathered.
anyways just plan that down the road you might get tired of riced civics passing you and want to regear.

 

[JAS]

I would defiantly go with the RE 3.5 lift. I love mine

I went about 2 years before getting 31's and I did not have much benefit in the lift because I still had 28 inch all season tires.

I then got the GY 31x10.50 tires and saw a huge increase in off road performance. Living in MI the AW4/3.55 was tolerable but just barely. In CO you might find it really bad but I think it is doable for a short period of time. Say 1 year. depending on your driving habits.

Over this winter I went from 3.55 to 4.88 gears and lockers. I am still breaking them in but around town I love it. Although 31s with 4.88s might not be for everybody.

 

[mgreen84]

6.5 inch lift, and 33 inch pro-comps.... been rockin' 3.55's from day 1..... but if the opportunity presents itself I would re-gear.... not really in a hurry

 

[garr]

31s, 4.10s & 3" of lift is in my opinion the best combo for use as a daily driver/Light duty trail rig.
Adding a rear arb adds lots of trailability if you can afford one.

 

[MrShaft696]

235's too close to stock...MAN UP!

 

[badron]

99% of all offing is done on 29.5~33, open diffs, stock engines. I ask is anything bigger then 33 worth it.









I would kill for a real locker

 

[BADaXJ]

go for the 31's. if you think there is any chance at all you might go bigger in the future, wait to re-gear. you don't want to be stuck with 33's and 4.10's, wanting deeper gears. i had a comanche 4.0 aw4 with 3.55's and 31's. i swapped in some 4.10's and it was nice but the change was not as big as i expected. i had 31's on the xj with 3.07's and it was fine. went to 33's and 3.07's for about a year. that kinda got old but it worked. sometimes on the highway i would run 4th gear. then i got 4.56's. wow, what a nice change. imo, 4.10 isn't worth the trouble/ cost of regearing. wait till 33's and get 4.56 or 4.88 if you think you might go bigger...
4.56 with 31's would probably be ok too. my 2 cents, don't bother with 4.10's...

 

[shanesaw]

I drove my 4.0-Auto on 31" tires with 3.55GR for 15 years. When my rearend went out two years go I replaced the carrier and 3.55's with 4.10's and hardly noticed any difference from the old GR. No change in MPG either. I have to agree with most of the posters, go with the 31's on 3.55 and regear down the road. You may decide you want to go with a bigger tire size, and if you do, those 4.10's won't do you any good.

 

[Tonytj]

4.0L auto on 30" BFG's, with stock 3.55 gearing. Absolutely no problems at all. The extremely minimal loss in acceleration or highway performance can be made up with a good catback.

 

[collkid]

i rock 31's with the stock 3.55

Just noticed that it shifts more, thats about it.

Here in Rocky Colorado, even in the mountains, doesn't really bother me.

 

[rocknxj]

31's and a 3.5" lift is a VERY nice combo. Affordable, yet capable. No SYE needed in most cases, gearing is tolerable, and you can up the ante by adding a better track bar and sway bar discos.

I ran that setup for 3 years before giving the Jeep to my kid. Now he loves and drives it with no complains. Of course, what you REALLY want is a 5.5" lift and 33's.....

 

[casm]

31's and a 3.5" lift is a VERY nice combo. Affordable, yet capable. No SYE needed in most cases, gearing is tolerable, and you can up the ante by adding a better track bar and sway bar discos.

Agreed. I ran pretty much this setup as well for close to two years, and it was very capable. I'll still toss my hat into the ring for 4.10 gears rather than 3.55s, but you can live with 3.55s on 31s - it's not ideal, but for starting out it'll be fine.

The one exception I would make to that would be if you tow at all; 3.55s, 31s, and a car on a flat trailer behind your XJ going uphill is not fun with that combo.

 

[kastein]

I used to think 32s/33s on stock gearing was "just fine". Sure, it doesn't accelerate like it used to...

Then I bought an MJ with stock tires and gearing and realized just how big a difference you feel. You can run stock gearing, sure, and there isn't as much of a difference in 4Lo, but you will feel it, and you won't realize it if you creep up in tire size unless you get back into a stock rig.

EDIT: further, don't regear higher than you might want, I'm only going to 4.10s because I'm on a budget and I picked up an 8.8 with 4.10s already in it. If you're paying for gearsets and install, and there is ANY chance that you will be going to taller tires in the future, gear ahead of your tires. Just don't go absolutely overboard with it and do something silly like 5.13s and 31s.

 

[recycledxj]

My last jeep had 3.55 gears with 33s and it was ok, until I voluntered to tow my buddys pop up camper with camping gear up to the mountains and it was horable. Found a set of factory geared 4.10 axles and it was great. My current jeep is a 5spd with 3.55 gear swaped in with 31s and does awsome til I get to the mountains. I don't do this often but I can burry the speedo in 5th gear.

 

[chelms27]

I had 31's on 2.5 to 3" of lift and daily drove and wheeled it very often in California. On a trip from California to Nebraska I averaged a hand calculated 21mpgs going 65-75 mph loaded with 280k on the odometer(97 sport) I now drive a 97 country (140k) with 235's 50+miles one way every other day and get 20mpgs average 55-75mph, goes down to 17-18 city. I just ordered some 31x10.50x15 BFG mud terrain KM2s and a 2.5" DPGoffroad hybrid lift and plan on 18-20mpgs. i know a lot of people say to wrap out the 4.0 but I think 31's on stock gearing is a good setup for a DD in my experience 6+ years as a DD. 4lo on trails will do very well IMO on 31's and stock gears.

 

[Vanimal]

I had 31's on 2.5 to 3" of lift and daily drove and wheeled it very often in California. On a trip from California to Nebraska I averaged a hand calculated 21mpgs going 65-75 mph loaded with 280k on the odometer(97 sport) I now drive a 97 country (140k) with 235's 50+miles one way every other day and get 20mpgs average 55-75mph, goes down to 17-18 city. I just ordered some 31x10.50x15 BFG mud terrain KM2s and a 2.5" DPGoffroad hybrid lift and plan on 18-20mpgs. i know a lot of people say to wrap out the 4.0 but I think 31's on stock gearing is a good setup for a DD in my experience 6+ years as a DD. 4lo on trails will do very well IMO on 31's and stock gears.

i think it needs to be clear for some people that a manual trans has 3.07 gearing, and not the 3.55 gearing with automatics that most if not all people are talking about when refering to stock gearing. 3.07's and 31's is a bit rough. not horrible, i did it for a little while, but my clutch hated me when wheeling.

 

[Antiferret]

i noticed a loss when going to 31's.

when i put on injectors from a local car here (holden commodore-uses a refined version of a buick 3.8) i regained my accelleration + a wee bit more (as measured against a mates stock xj). also bettered my mileage as transmission didn't have to do as much downshifting staying in higher gear(at 100 kph, prev 480klm per tank hwy, now 540klm)

do it, get the injectors (more holes for atomisation is the key, see writeups here on chrysler neon swaps) and drive slower as indicated by your speedo, police don't accept bigger tyres as an excuse for speeding!

 

[OutkastBoss]

I went with a DPG Offroad 4" Ome hybrid Kit and didnt end up needing the sye in my 2001.

I noticed a loss with an Auto when i went to the 31's but it was tolerable for sure and did WAY better on the trail than with my little stock sized tires.

I Later Regeared to 4.56 and its a bit low for me but its fun to drive with that extra oomph and still does fine on the Hwy..
I geared it for my 33's i intend to buy and dont want to go any larger than that

 

[djlarroc]

curious to know what op ended up doing. he's had 2.5 years to mull over the decision.

 

[IslanderOffRoad]

I loved my xj with 31s and the RE 3.5, extremely capable combo that I wheeled all over so cal and Moab.

It was good with 3.07s... And got great when I went 4.10s