Wheel backspacing and tire fitment for 37's and 38's

#1
I'm looking to upgrade to 37x12.5R17 or 38x13.5R17 Milestar Patagonias and I am having trouble finding accurate information on tire fitment, specifically tire rub on the inner fenders, sway bar, and lower control arms.

I currently have OEM Rubicon 17x7.5 wheels on 1.5" Spidertrax wheel spacers, which effectively reduces my backspacing from 6.25" to 4.75". I have no tire rub issues with my 35x12.5R17 Cooper Discoverer ST-Maxx's (MetalCloak 3.5" springs). One of my buddies has 37x12.5R17 Nitto Ridge Grapplers on 17x8.5 AEV Pintlers with 5.25" backspacing, and his tires rub pretty significantly. He had no tire rub with his last set of tires, which were 35x12.5R17 BFGoodrich M/T KM2s (3.5" AEV springs).

Obviously, the standard 4.75" backspacing of most aftermarket Jeep wheels will be fine for the 37x12.5's I'm looking at, but I'm concerned that the 38x13.5's will require less than that to keep the front tires from rubbing when stuffed/steered. There are a handful of 4.5" backspaced wheels on the market, but I'm wondering if that would even be necessary. Does anyone here have some experience-based advice? I'd like to run as much backspacing as possible to minimize the scrub radius and the load on the balljoints, but I don't want to deal with tire-to-metal rubbing either. I can adjust my bumpstops, but I'd like to retain as much uptravel as possible. I've picked up some MCE fenders to open up the wheelwells and I plan to upgrade to MetalCloak's control arms to properly center the rear axle. I'm also aware that I will need to trim the pinch seams to gain some more fender clearance as well. But before I buy new wheels, I need to make sure I'm getting ones of the right dimensions to keep the tires off the parts that I can't do anything about.
 
#2
While I don’t have experience with those particular tires, I do have experience with using the OEM JK wheels with several other brands and sizes. My advice to you is to mount your new tires on your JK wheels. I do mine by hand to save a few dollars. Put 10 ounces, by weight, of good quality air soft pellets (Golden Ball are super smooth and last a long time with no air bubbles) in each tire. Then start driving with your current wheel spacers. Mounting them yourself and using the air soft pellets will save you money if they do not work out for you on your wheels. JK wheels are also very plentiful. You can use pick up a set for $100 that you can use to test fit your new tires, or to mount your old tires to use while you are messing with your new tires.

One other item you can adjust is the steering stops on your front axle. I know people are afraid that they will lose some turning readies, but you won’t miss it.

BFG tires typically measure smaller then their spec size which is why your friend is experiencing issue now. Depending on where he is rubbing, adjusting his steering stops may reduce that rub significantly. You can check the actual tire sizes on the manufacturers web page. If the actual sizes are not listed, then don’t buy those tires.
 
#3
I'm asking for fitment experience for specific tires of specific sizes on wheels of specific dimensions; I'm not interested in continuing to use OEM wheels, especially since I'm looking to mount 13.5" wide tires and they're simply too wide for the 7.5" wide OEM wheels. I don't see what the purpose is of the suggestion that I buy another set of OEM wheels to mount my old tires on to use while I'm "messing with the new tires." I don't want to "mess" with anything - I want to buy the right size and offset wheels to mount specific tires on and minimize or eliminate tire rub.

Airsoft pellets have nothing to do with my question.

I'm not going to adjust my steering stops because I absolutely will miss the lost turning radius. Anyone who drives tight mountain trails needs every half a degree of steering angle they can muster. These long-wheelbase Jeeps have horrible maneuverability already, so reducing the steering angle only makes a bad problem worse. But I'm not asking about tire fitment with modified steering angles; I just want to know what backspacing people recommend for the specific variables I presented.

My friend's tire rub issues have nothing to do with BFG's tires and their sizing inaccuracy; he has Nitto tires. And they rub when pointed straight ahead with the suspension flexed because the AEV wheels' 5.25" backspacing is excessive. He could add bumpstop spacers to limit suspension uptravel, but that's a band-aid, not a fix. His tires rub the inner fender when the tires are straight, and the sway bar and control arms when steered, not the underside of the fender flares; tire diameter is not his problem, wheel backspacing is. This is why I'm trying to determine if 4.75" backspacing will be sufficient for the specific setup I've described, or if I will need to go to 4.5" backspacing.

And as we discussed in a different thread, the actual tire sizes listed on manufacturers' web sites are bunk. That's why I'm soliciting advice from people who have experience fitting the specific Patagonia tires I've mentioned.
 
#5
I am going to apologize for my posts that have obviously affended you. My intent was to sincerely help you with the experiences I’ve had with my JK and fitting tires to it. I do hope that you find someone that lives in the same region of the world as you with he exact same springs rates and Jeep that weighs exactly the same as yours so you can get an exact reference as to how these tires will work on you vehicle.
 
#6
I'm not offended, and I appreciate your effort to help. I just need information from someone who has used or seen 37" and 38" tires on a JK, and who can offer advice on wheel backspacing. I was merely explaining why, as appreciated as it was, your input wasn't answering any of my questions; I hadn't made my questions clear enough.
 

Pthorpe84

Moderator
Staff member
#7
I will tell ya, you will have some rubbing issues. My slabs are at 3.5” backspacking and I get some rubbing while flexed and the steering turned. I am running 37X13.50 Toyo’s. Being that the stock wheels are so narrow, you should look at some aftermarket wheels. Especially with a 13.50 wheel. All other rubbing can be solved with added bumpstopa. Depending on your lift, you may need to trip some sheet metal and hammer some of it out. If you would like I could post some pics of where I trimmed mine. I ran and wheeled 37’s with no lift for about 18 months.
 
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Pthorpe84

Moderator
Staff member
#8
I can adjust my bumpstops, but I'd like to retain as much uptravel as possible. I've picked up some MCE fenders to open up the wheelwells and I plan to upgrade to MetalCloak's control arms to properly center the rear axle. I'm also aware that I will need to trim the pinch seams to gain some more fender clearance as well. But before I buy new wheels, I need to make sure I'm getting ones of the right dimensions to keep the tires off the parts that I can't do anything about.

To keep your up travel you will need to get the MC Overlines to keep that. The MCE’s not offer much uptravel outside of trimmed stock fenders. You should have no issues with getting a good wheel at 4.5” backspacing. I had some pintlers with those dimensions and did not have much trouble with rubbing.
 
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