Upgrading from 30" to 31" tires, problems?

97XJ, 4.0, 231J, 3" Old Man Emu Lift.
OME JC1A Rear Leafs
OME 930 A&B Front Coils
OME 36C Rear Shocks
OME 35C Front Shocks
Original control arms.

Currently running 30" Goodrich AT's.
Need to replace tires and would like to know what would happen if I buy 31" new tires?
Do I need new control arms?
Do I need more lift?
DO I need fender trimming?
If it isn't too complicated or expensive, I would really like to put on 31's.

Any advice is appreciated.

97XJ, 4.0, 231J, 3" Old Man Emu Lift.
OME JC1A Rear Leafs
OME 930 A&B Front Coils
OME 36C Rear Shocks
OME 35C Front Shocks
Original control arms.

Currently running 30" Goodrich AT's.
Need to replace tires and would like to know what would happen if I buy 31" new tires?
Do I need new control arms?
Do I need more lift?
DO I need fender trimming?
If it isn't too complicated or expensive, I would really like to put on 31's.

Any advice is appreciated.

31s no lift with WJ lowers.

I ran without rubbing at stock height on 30x9.50 tires. With 31's, i rubbed at 2" of lift. The Jeep also got *much* slower when trying to climb hills on the freeway - way more than the 1" would have led me to expect. If you have 2.5" or more lift, you'll probably be fine - but go into it knowing that mpg, mph & braking distance will hurt a bit.

My 97 XJ with 30x9.5 and 2.5" lift is noticeably slower than my 01 XJ with 235/75R15 and at stock height... both have stock 3.55 gears. If you go to 31" tires you'll probably wish you had 4.10 gears. I think its the width as well as the diameter that makes the difference. Never driven a stock XJ so I don't know how stock vs 235/75R15 would compare, but it seems even 30x9.5 slow it down... My 01 XJ with 235/75R15 also gets much better fuel economy... So take this into account. I've also heard 31's can bend the factory tie rod. I've bent the factory tie rod even with 30x9.5 and nothing too difficult... So basically a bunch of areas need to be improved or should be considered for improvement before moving up to 31's and long term reliability.

I answered in you double post in the OEM section...

Both my XJ's have or had 31's on 3 lift. A little trimming of the plastic is all that was needed with 4.25 offset rims. Stock rims will likely rub the control arms and the plastic.

3.55 gears are not ideal, but will be useable and adequate for most. The stock steering will be fine unless severely abused.

FYI. 30's to 31's is where most people lose the most fuel mileage. Seems that extra inch is just too much for stock gears. Expect a 2-3mpg loss.

JohnX said:

FYI. 30's to 31's is where most people lose the most fuel mileage. Seems that extra inch is just too much for stock gears. Expect a 2-3mpg loss.

Click to expand...

Try goin from 235/75R15 to a 33x10.50R15 KM2 with 3.07 gears lol I went from 20-22MPG to 12-14 :eeks1:

I did this during this year and my 31's do rub on my lower control arms at lock. I am keeping my stock rims so I am adding wheel spacers. What I did to add the 31's, admittedly my springs were pretty bad, was a 3 inch lift with new front springs and AAL (am replacing with new leafs after the first of the year), tubular lower control arms, adjustable track bar and have the parts but not installed V-8 ZJ tie rod and drag link. My rig is not a hard core off road rig but see trail duty on our farm and hunting lease. Most common obstacles are mud or drainage ditches. Not a whole lot of rock crawling in southern Louisiana. My goal was a general duty on/off road rig for hunting and fishing with occasional towing of my boat. I have a Renix Jeep and the torque curve on the motor is very different than the H.O.s and haven't noticed much of a decrease in performance. I do however plan to upgrade to 4.10's in the future.

I did this during this year and my 31's do rub on my lower control arms at lock. I am keeping my stock rims so I am adding wheel spacers. What I did to add the 31's, admittedly my springs were pretty bad, was a 3 inch lift with new front springs and AAL (am replacing with new leafs after the first of the year), tubular lower control arms, adjustable track bar and have the parts but not installed V-8 ZJ tie rod and drag link. My rig is not a hard core off road rig but see trail duty on our farm and hunting lease. Most common obstacles are mud or drainage ditches. Not a whole lot of rock crawling in southern Louisiana. My goal was a general duty on/off road rig for hunting and fishing with occasional towing of my boat. I have a Renix Jeep and the torque curve on the motor is very different than the H.O.s and haven't noticed much of a decrease in performance. I do however plan to upgrade to 4.10's in the future.

You live in Louisiana, so the stock gearing won't be nearly as much an issue with the larger tires than if you lived in a mountain state. If you go bigger than 31s you might start having an issue.

Well that may be true but we do have hills in Louisiana, the other thing is that Renix motors torque band is different that the H. O. motors with a stronger torque curve down low. Renix Jeeps also usually get better gas mileage in stock form with all else being equal. In fact the only area where the H.O. motors best the Renix is in top end horsepower and then only by 8 h.p.

Typically, when you go larger than 30 " tires stock-ish you lose MPG.