Larger sized tires on rear

[Seb1008]

Hello, I have a 2 wheel drive xj, 2" lift with a Sparten locker in the rear. For the past year and a half I have camped in the western US full time.
I pull a small 4'x6' trailer and am presently running on General grabber 235/75/r15 at2 tires. I would like to put larger mud tires on the rear as 75% of my driving is on gravel or dirt-sand roads. Either 30s or 31s preferably 31s. Looking at wild peak or federal couragia.
would this affect the xj or be hard to steer? I'm 67 and drive like a grandpa, mostly drive back roads and 55 is top speed. Finances are limited as im on disability, thats why i would only get 2 at this point.

 

[Tim_MN]

At 2" of lift, 30"s will fit, 31's will rub.

I do not think it is wise to have unequal tire sizes, it will throw off the suspension dynamics, especially is you need to make an emergency maneuver on the highway. If you have a flat and install different tire sizes on a automatic locker, it potentially could damage the locker. You could do that to get back to town, but now you would need to find a suitable tire size where you may not have many choices.

If your budget is tight, you should look for used tires from somebody upgrading. Facebook, CraigsList, or for oldtimers like us, the local owned independent tire shop. I have come across lots of good deals on sets of tires with plenty of remaining tread life.

 

[Unclewolverine]

If you want cheap traction I use accelera M/T-01 size 235/75R15 on my mail jeep, very cheap, very good traction, never got a rock puncture. Wear very quickly though, bald in 20k very hard miles.

 

[Vince]

In theory a 30x9.50R15 is around 1.1" larger diameter than a 235/75R15 28.9".


In reality, the actual dimensions provided by the tire manufacturer may reveal a different story. I have seen dual marked tyres before in this size where a slightly larger 235 was dual marked as a 30 but was actually smaller than most other brands of 30x9.50R15.


The 30x9.50R15 Falken Wildpeak M/T is 29.6" diameter
The Federal Couragia MT is available in 235/75R15 and 30x9.50R15 but they have not published the diameters.


A BFG KM3 235/75R15 is 28.9" diameter
A BFG KM3 30x9.50R15 is 29.5" diameter
A Cooper STT Pro 30x9.50R15 is 29.57" diameter


So depending on make and model of tire, a 30 will give you roughly 1/4" to 1/2" greater ground clearance depending on how the tires sit when inflated. If obtaining the correct on street contact patch requires you to run the MTs on the rear softer, there might be no detectable difference in rolling radius.


Normally, I would always run the same make and model tyre on all wheels including the spare so I can rotate them regularly for even wear. As your Jeep is a 2wd, rotating mixed tires at service interval would be something you probably would not want to do.


Mixed tires, and directional tires force an awkward choice when it comes to the spare.


If you get stuck for traction on mud with your AT's and you have snow chains with you, put the chains on the rear tires. Snow chains work surprisingly well in mud.