I see tire/wheel questions asked a million times, but I am trying to back into the correct tire size...

I bought a used 2008 Jeep (manual transmission) and was told it has a 4.5" lift (forget brand it was a few years ago) with a 5.13 gearing. It currently has 315/75/16. It is more of a play vehicle, but I do drive it to work sometimes which is 80 miles round trip. I have never reset my speedo, but highway speeds I am turning 3k rpms... The tires are Mickey Thompson Baja MTZs and when I measure them I even though they are suppose to be "35"s I only measure 33ish inches and the spare on back under 34" (no weight on it)...

I need new tires. I am probably not keeping the 16" rims and moving to either 18s or 20s. I see all kinds of questions about which gears to run which each tire size.... If I really have 5.13 gears, should I go ahead up to the 37s? It should bring my rpms down, correct? What real issues does it create? I will admit I am a poser and the Jeep is 100% on the road. My current spare is humg off the default spare tire holder. Will I have to change that or is it just preferred to change it?

My other question, is... I was looking a Terra Grapplers and for 37" it has a minimum of 10" wheel width. I see plenty of "dealers" on ebay selling 37"s with a 9" wheel. Which is correct? 10" width defintely pushes the price up more than I really want to spend...

 

You realize that those tires are 14" wide, right? Which may be why they give that rim width recommendation. Shouldn't be a problem to run them on a 9" wide tire, assuming your shop will mount them -- but -- pay attention to the backspace recommendations in the sticky thread at the top of this modified area when you go to buy your new rims. Even with a low backspace on the rims, you will likely be buying wheel spacers also.

To check the RPM's, open the faq's (another of the threads stickied right to the top of this modified area), scroll to the drivetrain section, and plug some numbers in.

You will want to go ahead and get a programmer to adjust the speedo.

You will want a new carrier capable of handling that big of a spare tire.

If you haven't strengthened the front axle, consider having gussets welded in. And it wouldn't hurt to get pricing info on a truss/sleeves/alloy rear shafts/ball joints/upgraded mounts/etc. Not that you will definitely need any/all of it, just keep the info handy 'just in case'.

 

No I did not know it was 14.5" wide...

What would be a good 37" tire subsitute?

 

Bfgoodrich makes some 37's as does Interco tire. You'll limit your tire choices if you decide to do the 20's because typically those tires (size and rim wise) are designed for larger trucks that can handle it. An Interco m16 may suit your needs. Another option would be mickey thompson atzp3, their stz (if it's in that size), or dick cepek's new fc's.

 

Just out of curiosity, why are you thinking about running an 18 or 20" wheel?

 

Here is my current Jeep. I like the wheels ok that it came with but would rather have something else. I only put 5k-8k miles on it a year, so whatever I do I will have a long time. So this decision will be with me for probably 5 years (or til I get something else). As much as the hardcore Jeep guys fight it, it seems larger wheels are taking over the market. Like I said, my truck might see a dirt road and that is about it, so I am not worried about scratching the wheels.

I really want 37s (look better and bring down my rpms) and don't mind the initial extra cost. It sounds like the longer term cost (breaking/bending things) will keep me from it. I was hoping if she was a pavement queen, the larger tires wouldn't really strain the components as much as I have been reading it can...

 

If you really do just use it on the road then you should be able to get away with some lighter all terrain 37's without any serious issues.

 

You might check a few for the 17 inch rim also, they seem to be a bit narrower than what you were looking at for the 18 or 20 inch rims sizes.

In addition to the Nitto Terra's, these AT's may be decent options.
BFG AT, Falken Wildpeak/RockyMountain, Dick Cepek Fun Country

I am running the 325/80/16 (37x12.50x16 equivalent) Rocky Mountain now. Great tire so far, might be a good option for your needs.

Again, keep the backspace suggestions from the thread stuck to the top in mind. You want the tires out far enough that they won't rub the frame or components in the wheel wells any time you turn and hit a dip in the road. (either that, or add washers to the steer stops and lose a bunch of your turning radius).

 

Falken wildpeaks are considered one of the best all around tires on the market...