Incredibly stupid question - 30's vs 31's

anthrax323 · Jul 13, 2010

Hey guys,

My MT/Rs are at about 1/32" tread depth and are beginning to concern me, so I'm going to invest in new tires this week. I'm ultimately shooting for only 3.5" of lift, and now can't decide if I want to go the 245/75R16 route or step up to 265/75R16 (will be buying Goodyear Wrangler DuraTracs).

Given that I'm still on stock gearing at the moment, I'm inclined to believe that the 30's would be more ideal. It seems like I'd be less likely to need to trim with the 30's, but would love input from those who have tried to make this decision.

If possible, feel free to post any photos you have of rigs running 30's on 3.5" of lift... I guess I'm just concerned as to whether or not that extra 1" diameter would make any worthwhile difference.

Thanks in advance!

420BlackXJ · Jul 13, 2010

Get the 31's. With 3.5", you can extend your bumpstops to avoid the need to trim, at least in the rear. Front, you may still have to trim the plastic bumper endcaps. I have 3" rear, 2.5" front. With front swaybar connected, I don't rub at all with 4" BS wheels. The rear with no swaybar, rubs alot before bumpstopping.
(added 3" to rear bumpstops.)

anthrax323 · Jul 13, 2010

Thanks for the input - I'm running some Mopar Moabs (TJ Rubicon rims), which are 8" wide with 5" backspacing (placing the outer edge 0.5" further out than stock XJ 15x7's), and I'm really wanting to retain stock flares and avoid any and all sheetmetal trimming. Are there any justifiable advantages to having the 1" of extra tread and overall diameter?

The only thing I can think of is a theoretical 0.5" gain in ground clearance (under the diff) - is that substantial enough to really take into consideration?

Monkey55 · Jul 13, 2010

anthrax323 said:
It seems like I'd be less likely to need to trim with the 30's, but would love input from those who have tried to make this decision.
..

30s would easier all around. You wouldn't notice the drag as much on stock gears and it probably wouldn't rub the fenders.

There's really not that much of a difference.

You don't necessary have to 31s because they are bigger. You would be able to go everywhere and do the same do stuff with 30s as you would with 31s.

If you are going to be doing a lot of highway driving, I say go for 30s. But if not, either way would be good.

E

1990JEEPXJ · Jul 13, 2010

Monkey55 said:
30s would easier all around. You wouldn't notice the drag as much on stock gears and it probably wouldn't rub the fenders.

There's really not that much of a difference.

You don't necessary have to 31s because they are bigger. You would be able to go everywhere and do the same do stuff with 30s as you would with 31s.

If you are going to be doing a lot of highway driving, I say go for 30s. But if not, either way would be good.

E

x2. not really much of a difference.

Monkey55 · Jul 13, 2010

anthrax323 said:
The only thing I can think of is a theoretical 0.5" gain in ground clearance (under the diff) - is that substantial enough to really take into consideration?

Nope.

anthrax323 · Jul 13, 2010

Rock on. 30's it is. Thanks a ton for the input!

Darky · Jul 13, 2010

I ran 30's on 3" lift up front and 1.5" out back, with heavily cut fenders and liked the overall look. Before cutting the fenders and after removing the swaybar, I smashed the fenders. They self clearanced. Which is why I cut. But I was still on stock bumpstops. Bumpstop properly, you'll have plenty of flex and not smash your fenders. You could even do a minor trim job that no one would ever notice and squeeze out some more room. I would recommend defintiely cuting and folding the pinch seam in the fenderwell.

30s no trimming - You can somewhat see where I messed up my fenders.

30's with trimming. I did a bad job. I plan on getting new fenders and being more careful with it.

Sort of at ride height after cutting. To give you an idea, I cut to about an inch below the body line.

Like this, I still got 19mpg and had enough power to keep up wit traffic and outrun it on occasion.

NW-ZJ-SCOTT · Jul 13, 2010

I really think this subject is just a matter of opinion, My opinion is
2" lift 30s
3" lift 31s
4" lift 32s
4.5-5" 33s
5.5-6.5" 35s

etc etc. I bought my XJ all stock, with 30" tires. and i trimmed for offroad use. Im sure 2" of lift i could of avoided ANY trimming..

Builderxyz · Jul 13, 2010

I run 30's at the moment with a 3" lift and run all over the place,also dont notice any loss of power with them.run them and have fun lol..

anthrax323 · Jul 13, 2010

Thanks for all the details guys (and the pictures - that helps me visualize it a lot better). In the end, I'm opting for 30's just because I really don't want to hack my Jeep to bits to get them to fit correctly over time (not to mention the gearing concerns, at least for the moment). I put in my order for a set of 4 Goodyear Wrangler DuraTracs (245/75R16) and am having them installed tomorrow. I'll post pics once available.

winkosmosis · Jul 13, 2010

245/75/16 is 31"

OK Cherokee · Jul 13, 2010

That's what I thought.....I was looking at the 265s which are about 32" tall.

anthrax323 · Jul 13, 2010

245/75R16 is a 30, from my understanding... Well, 30.5 x 9.5. The next jump is a 265/75R16, which I always thought was commonly considered a 31 x 10.5 (though it technically measures out a bit larger than 31). Am I off my rocker on this one?

blondejoncherokee · Jul 13, 2010

youre right this is an incredibly stupid question.

OK Cherokee · Jul 13, 2010

I wouldn't say stupid...but doesn't really matter either way.

To the op: a 245 is 30.5" and a 265 is 31.6...BUT depends on what brand you're measuring since all different tires seem to measure out differently.

cwstnsko · Jul 13, 2010

In the Tire you have ordered, the 245/75-16 is about the equivalent of 31x10, the 265/75-16 is about the equivalent of a 32x10.50. Most 31s are actually about 30.5 and Most 32s are about 31.5. The revolutions per mile rating can be useful for comparison, this is what affects your gearing and speedometer reading.

One thing to watch for on 16" tires for an XJ is to try and find load range C tires and try to especially stay away from load range E. The HD tires ride harsher and may not behave like you are accustomed to when aired-down.

OK Cherokee · Jul 13, 2010

Good call on the load range comment!

xcm · Jul 14, 2010

we dont get jeeps to run small street tires, get the biggest tire you can fit, 31's are the smallest tire i would ever put on an xj.

kndrewa · Jul 14, 2010

Monkey55 said:
30s would easier all around. You wouldn't notice the drag as much on stock gears and it probably wouldn't rub the fenders.

There's really not that much of a difference.

You don't necessary have to 31s because they are bigger.
You would be able to go everywhere and do the same do stuff with 30s as you would with 31s.

If you are going to be doing a lot of highway driving, I say go for 30s.
But if not, either way would be good.

E

x3

I have run 245/75r16s on 3.5" with 3.55s for 5+ years with no issues.
A bit of trimming is all you need in the front - i took off an inch or so with an angle grinder.
I only cut in a few places (marked in blue) in the rear with tin snips and hammered the resulting 'flaps' in with a sledge.

I haven't even had a need to bump stop
plenty of clearance for plenty technical wheeling:

Incredibly stupid question - 30's vs 31's

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