I'm about the replace the E rated 305/65-17 BFG AT KO's on our JKU. I'm looking at going with Nitto Trail Grapplers. I'm torn between the E rated 295/70-17 and the D rated 315/70-17. Honestly, the JKU is driven by my daughter 90% of the time. Mostly street driving, dirt roads and some light mud occasionaly. My BFG's are about 32 1/2 inches tall and do ride a little rough. I want to go up in size. The 295 Nitto's are about 33 1/2 inches tall and the 315's are about 34 1/2 inches tall. So I'm wondering if the softer sidewalls of the 315's will actually "squish" more than the stiffer E rated 295 and result in about the same overall diameter and effect on gearing. Also, will the D rated 315's ride noticably better than an E rated tire? In all honestly, I just want larger tires but I don't want to totally kill the performance of the weak 3.8V6/auto/3.73 gear setup we have. Opinions?

 

E rated tires are not made for Jeeps, but for heavier vehicles, and have stiffer sidewalls than the D rated.

The ride on E tires is noticeably harder than on D.

 

I would definitely go with D rated. The E rated is overkill for a JK and yes it will ride stiff, and you have to run them at lower psi to get a decent ride with them.

 

Yeah, the E rated BFG's we currently have are pretty stiff even running them at 30 PSI. I know I need a D rated tire but I know the almost 35 inch height of the D rated 315/70-17 is gonna strain my powertrain even more.

 

30 psi is normal pressure for D tires, so you may want to try less on the E.
Depending on your specific Jeep, it might be a bit softer, but not like D.

 

Regear it.

Then get the C rated 40's. Your daughter will love it! Or maybe just the C 285's...

 

Yep, I agree. Even C rated 35s rarely chalk test to 30 psi.

 

I think you should read some threads on gearing. I don't have the 3.8, but from what I have picked up, you don't want to go past 33" without regearing. I drove a 3.8 JK with 35s and stock gearing and could barely get it to 70 on the highway.

 

I had bought my duratracs before I realized they were E rated. They are a heavy tire and I'd suggest getting the D or less.

 

So hard to find 315 or 35 in a D rating and not lose something. All the tires I wanted were E and the mtr/k that I had were E and rode awful.

I went with the big o xt in a 315 with a D rating, they are much better.

30 in the front 28 in the back