I am looking to fit 275/70/18 (33.4") ST MAXXs to replace my 255/70/18 (32.2") Duellers. My real concern is going from 39lb per corner to 60lb, I have 3.21 diffs. How much, in the 'real daily driver world' am I going to find the additional 20lb per corner affects the drive of the Jeep?

 

With 3.21's its going to be sluggish and you will visit the gas pump more frequently

 

It will. I had 3.21s and went to 33 Duratracs and then to 35 KM2s. Drove it with both. 33s are OK but 35s kinda make it a dog outta the hole. It's liveable but I saved my money and put 4.10s and a rear locker in.

I would do it. You can always go back smaller if you hate it that much.

 

With the 3.21 ratio I'm assuming you have the manual trans. You will find that 6th gear is no longer useable and that 5th isn't much better in the hills. The biggest issue I have had since going bigger with mine (3.21s with 6spd) is just that. I recent got a Flashpaq and it has made things better, but a regear is still in my near future as I am moving up to 35s when my MTRs wear out! You may wear your ball joints out faster depending on how much you take it on the trails and how hard you wheel it. And there is the ever-present boogey man that will bend your inner "C"s on your D30 axle... I wheel the crap out of mine and haven't bent anything...yet! Thats what I see you running into, I'm sure others will chime in with their own opinions and advice as well.

 

I probably should have added more info, i'm in the UK so we're talking the 4 pot diesel (197 BHP and 390-something lb ft of torque). The transmission is the 5 spd auto and it's a 2013 JKU.

The jeep really shifts on full throttle but half throttle does seem sedate.

I love the JK, smiles every time i drive it but the niggle that it feels slow unless i'm pessing on. I'm guessing 60lb Coopers and a heavier right foot is the way forward.

 

Wish they had the diesel JK here. Im sure with that much torque you would be fine.

 

i think with the low end grunt of the diesel right off the bottom you will be fine with the bigger tires. Not like you will be trying to set any speed records.

 

It's going to be horrible. Totally unbearable, even. You are going to kick yourself every single day for going up a single tire size when you knew you should be sitting on 35's. And then you would have a size/weight difference worth comparing...

 

I had the same size on my 2013 Sahara with a 6spd and it was ok. A lot of it was definitely the 3.6 helping me out. Give it a try and see what you think.

 

Yes, I was going to ask. It's a good idea to fill out your profile information. That was the first thing I clicked on to see if you provided us with this information. To be honest, I wonder whether anyone in the U.S. who has never driven a diesel JK could give a very good answer to this question. You have a lot more torque than either U.S. motor, and the torque curve is a lot different (and better).