Minimum Lift Needed to Run 31x10.50s?

I came into some almost new BFG AT's 31x10.50s

I have a 2" spring spacer laying around for the front, never used it.

How much lift do I need to fit these under my bone stock 92 xj 5spd?

Will they hurt my MPGs much?

Can I expect a smoother ride on washboards with the bigger tires? I air my current tires down quite a bit to get around Baja, thing goes anywhere but the miles and miles of dirt I drive rattle my brains and vital parts loose.

Not really going to do any rock crawling sort of stuff, mostly dirt sand and snow.

You can run 2 but you'll have to cut the fenders. I get about 14mpg average running 31's on a BB w/ stock gears( hopefully not for too much longer) but you have a stick so your results will be different. Mine rides just a hair stiffer than a stock XJ, You oughta be fine like that. I have had mine for 5 months or so and I have no complaints about the ride or handling of the Jeep.


Oh yeah and I have a heavy right foot sometimes.

31's with stock 3.07 gears? That sounds like a bad time. Although some people do it. Depending on wheels (stock or aftermarket) And bumpstops you may either rub at full turn lock or fenders. If anything remove flares and inner fender.

Johnnie Walker said:

31's with stock 3.07 gears? That sounds like a bad time. Although some people do it. Depending on wheels (stock or aftermarket) And bumpstops you may either rub at full turn lock or fenders. If anything remove flares and inner fender.

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Ha, didn't even think about the 3.07's! Oops!

My first XJ was an '84 (with the o-so-fun 2.8L V6) and ran 31's for 2 years...and the jeep felt every single day of it. I'm assuming you have the 4.0, the 3.07's count against you, but IMHO you can do it. Can you mash the on-ramp? No. Will it stress your Jeep more than your current set up? Yes (but possibly not by much). A 2" BB probably won't do much (but I understand that sometimes you got what you got, and that'll have to do), I was running 3" and had the following issues:

- Tires rubbing on lower control arms (remember most 31's will not only be taller, but slightly wider than most stock tires): premature tire wear/cupping and decreased turning radius.

- Decreased mileage: More rolling resistance, etc. One side-note to consider (and the one most people seem to forget) is that yes, your mileage reading may be shocking initially, but unless you're planning on correcting your speedo gear during your tire swap, your "trip" mileage to determine your MPG's will be off. Bigger circumference of the new tires means that for every rotation of the axle, you're actually traveling farther.

- Increased strain on axles and driveline: You're not running 35's on stock gearing (like I am bc I'm a dummy in need of a bigger paycheck ), but it'd be worth asking the wrench(es) aligning your XJ to check the drive shafts, u-joints, etc to see if they can catch any issues right off the bat.

- The larger tires should help you out in the sand and snow for obvious reasons though so that's a plus!

I'm not guru by any means, but figured I'd give my two cents having experienced 31's, 33's, and now (doh!) 35's on stock gears. And, there is a huge difference between 31's and 33's IMO. 31's are do-able with the proper precautions, and lift/fender triming/bumpstopping combos.

HTH

Ed

Johnnie Walker said:

31's with stock 3.07 gears? That sounds like a bad time. Although some people do it. Depending on wheels (stock or aftermarket) And bumpstops you may either rub at full turn lock or fenders. If anything remove flares and inner fender.

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I did it for about 9 months. Its ok, 5th is pretty useless though.

I also ran 31's at stock height for a couple months. Its doable, but will rub if you don't trim.

It's a manual so the 3.07 is equivalent to 3.55 on an automatic.


I have 31" with 2" lift and washers in the steering stops to prevent rubbing on the LCAs. Unless you flex, you shouldn't get any rubbing anywhere else as long as you use stock wheels.

My gas mileage went way down. I get about 15 or 16 mixed. The ride is much worse because of the angle of the control arms. That's what happens when you go from horizontal arms that allow the tire to move slightly back as you hit a bump, to angled arms that force the tires forward into bumps. This is the big big big disadvantage of solid axles-- if you lift, the ride has to become much worse. If you want a good ride and less wear on the unibody from washboard roads, stay at stock height and use 30x9.5 tires

I ran 31' Nitto's on stock wheels with a 1,5" Old Man Emu lift ... no problems on road/dirt. Once you start flexing you will rub ... lots ... you will need to extend your bumpstops.

Now i have a RE 3.5" Superflex lift and no problems at all...

IslanderOffRoad said:

I did it for about 9 months. Its ok, 5th is pretty useless though.

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same here. ran that set up for a while then regeared.

31's and 3.07 gearing is doable, but not ideal.

bump stopping is critical when running a low lift and big tires. i had the passenger side upper control arm hit the oil pan where it bolts to the block because i didnt bumpstop. with an auto trans xj, its possible to crush the transmission fluid lines to the radiator when this happens.

Well. OK then. So very glad I asked before falling in love with the idea of bigger tires.

Thanks all for the great info!

Joel

sure 31s and 3.07s is not ideal, neither is dropping out of school. but a lot of people do it anyways...

you have two options with 3.07:
1 - run it hard, scoot around town like you always have, and your gas milage will suffer.
2 - baby it, easy on the throttle, and get passed by grandma. but youll be sippin gas.

ive tried both extremes (4.0, AX-15, 3.07s, 4.5" of lift, 31s) and got about 250 miles on a tank running it HARD, squealing at every corner. then i got around 375 to a full tank absolutely babying the jeep. these were done with a fresh oil change, and all the way until the jeep was completely empty (i kept a can with me). now... your results may differ because i dont know the condition of your motor or even mine for that matter. i get about 300 miles to a full tank now, so i run her hard i guess. :dunno:

at 2" you wont need to mess with your drive line and get a SYE or anything. shocks may be alright, if not there are cheap alternatives. shackle or bastard pack the rear (very easy to do, dont let it intimidate you), all your clamps and hardware can be bought instead of made. if i can fit 30x9.50s with 5.25" of backspacing on saggy/stock height. you should be fine on 31s. just stay connected, you said you dont wheel hard anyway.





remember... stay in school.

Minimum size?

i run 31s on a 2.5" homebrew lift and a manual, i get no rubbing at all. i did have to adjust the steering stops with stock steelies, which decreased turning radius a little. i have also not done much to flex it yet, for now this is mainly a dd. as to making the ride harsher due to caster, when i did my lift i adjusted my caster with shims behind the lower control arms, it made a noticeable difference. cheap fix anyways. i am also still at stock 3.07 gearing, and so far it is working out ok. naturally, in the future i would like to regear, but for now it is not bad(not near as bad as i thought it would be). as said, 5th gear is pretty much useless, and my mpg did take a small hit........i was getting 15 in the city before, i think i get just over 14 now......but i have a pretty heavy foot. overall i find the ride much smoother than my 235.(btw, both old 235s and new 31s are BFG A/T).

89xj said:

bump stopping is critical when running a low lift and big tires. i had the passenger side upper control arm hit the oil pan where it bolts to the block because i didnt bumpstop. with an auto trans xj, its possible to crush the transmission fluid lines to the radiator when this happens.

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that happened to me once (crushed tranny lines). It sucked. Relocate them, bumpstops or not. I think part of the cause of that is the axle moving left due to the increased height but same length track bar.

I've been on saggy stock suspension, stock wheels, and 31x10.5s for about a year now. My fenders are trimmed, but it looks fine. The front fenders can be remounted easily a couple inches higher.

The tires will rub your lower control arms towards the end of the steering cycle in both directions. That is super annoying when trying to park and I think can actually damage the tires.

You shouldn't have any cupping/uneven wear if you keep the right amount of air in your tires. Putting a 10.5 on a 7" wide rim isn't as bad as a 12.5 on an 8" rim- which happens all the time.

Your 2" kit should do it, buy you may end up trimming. If you absolutely do not want to trim sheet metal, go for a 3". I like trimming, it allows you to run bigger tires without going higher. Looks just fine too it you take your time and do it right.