FLEX TEST : Will 37's Clear a JL Rubicon running 2.5" of Lift & Without Rubbing??

wayoflife

Administrator
Staff member
FLEX TEST : Will 37's Clear a JL Rubicon running 2.5" of Lift & Without Rubbing??

There was never any question for Cindy and I that JET Li, our brand new 2018 Jeep JL Wrangler Rubicon Unlimited, would be running a set of 37" tires and much sooner than later. What was in question was, how would we get there? How much lift would it take to clear them and could it be done with wheels that have a bigger amount of back spacing especially now that JL Rubicons come with 68" wide axles? In the end, we decided to run 37x13.50 Cooper STT Pros mounted on KMC XD231 beadlock wheels that have 4.75" of back spacing and try to make it all work with an EVO 2.5" Stage 4 Budget Boost, complete with all 8 adjustable control arms.

Soon after getting everything installed, an initial test drive showed us that this setup worked great or at least, around town anyway. The 2.5" coil spacer lift provided plenty of room to clear the 37" tires and we saw no rubbing at a full lock, in either direction and this in spite of the tires being 13.50 wide and mounted on wheels with 4.75" of back spacing. So, the real question now was, how would this setup do off road? Fortunately, for us, a good flex test was just down the street from us and the following are pics of what we found.

While ramping a Jeep or lifting it from one corner with a forklift can give you an idea of things, the best way to see just how much flex it really has is to get it twisted up. The opposing flex will force the axles to mash into the bump stops and drop the opposite side down to a full droop. Unfortunately for us, we were already hearing a good amount of rubbing well before we could work our way up into our testing obstacle but here we went anyway. For our first test - driver side front up and turned to the left.
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As you can see here, the front jounce stop or bump stop is fully compressed.
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In spite of how this pic may look, there is no rubbing of the tire on the driver side fender liner, coil perch, frame rail or other wise that we could see on the driver side and with the wheels turned to the left.
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At a full droop, the passenger side coil is still seated properly.
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Brake and ABS lines all seem to be good.
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Turning to the right to check for any rubbing or clearance issues.
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Here you can see that the tires clear the front bumper and grill.
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Amazingly, the 13.50 wide Cooper STT Pros tuck up and under the fender as well but then, a lot of this has to do with the 4.75" of back spacing that the KMC XD231's have.
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View from the back of the driver side front wheel well to show the fully compressed bump stop and shock.
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With the wheels turned, you can get a better look at the passenger side front coil bend.
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Moving to the back of our JL Wrangler to get a better look at things.
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With the driver side rear tire drooped out, we could see where it had be rubbing a bit on the lower fender liner that covers the bumper.
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On the passenger size, we could see that the tire was making full contact with the lower fender liner that covers the bumper.
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The bigger problem we found was that the lip of the main fender liner was catching on the tire lugs and getting pulled up. In fact, you can see that a push tab had already gotten pulled out. This was clearly the source of most of what we were hearing.
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Looking toward the front of the rear wheel well, we saw that things were clearing well. Certainly, no issues with the pinch seam or rock slider like you would have seen on a JK.
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Moving forward through the obstacle so that we can switch our twist.
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Verifying that we have full stuff by making sure that the bump stop is fully mashed.
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It's close but the back of the passenger side front tire just misses the fender liner when turning to the right.
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Turning about half way back to the left, the tread just kisses the fender trim as you can see here. Being that we are at a full stuff, this shouldn't be a problem.
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At a full stuff and lock to the left, everything clears and you can see where the tread just kissed the fender trim.
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Toward the front of the fender, you can see how the tire is just making contact with it here.
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And toward the very front as well.
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Like the driver side, the tire clears the grill just fine.
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Pushing all the way through the obstacle.
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Back on level ground, you can see where the passenger side front tire was brushing up against the fender liner.
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Looking back at the passenger side rear wheel well, you can see how mangled the fender liner got.
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The driver side rear fender liner fared better but I think it'll just be a matter of time before it gets mangled up too.
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And that concludes our first flex test running 37x13.50 Cooper STT Pros mounted on KMC XD231's and all sitting on top of an EVO 2.5" Stage 4 Budget Boost. As you can see, we'll need to head back to the shop and make some modifications. :cool:
 

wayoflife

Administrator
Staff member
FIX for the FENDER LINER

FIX for the FENDER LINER
Back at the shop and ready to get our fender rub fixed, I started out by removing the lower liner that covers the bumper. On the driver side rear wheel well, this is where we were seeing most of our rubbing and an 8mm socket and 3 screws removed later, this is what we were looking at.
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Again, using an 8mm socket to remove 3 more screws, this is what the bumper looks like without it's plastic end cap.
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Using a 16mm socket, I then removed the lower liner bracket with the hope that would clean the look of things a bit. Here's a few shots of what the rear end looks like with just the steel bumper installed.
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Moving over to the fender liner itself, I used a heat gun to help me reshape the embossing and concave it out of the way.
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That ought to do it!
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Not super thrilled with how the bumper was looking, Cindy and I decided to reinstall just the plastic end cap.
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As a reminder, this is what the passenger side rear fender liner looked like after our flex test.
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And, with the help of a heat gun and a bit of reshaping, this is what it looks like now.
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More of a profile view to show much I was able to push the embossed feature of the fender liner out of the way.
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With that, we should be good to go. Just gotta take JET Li back out on the same obstacle and see if the fix did the trick. :cool:
 

wayoflife

Administrator
Staff member
FLEX TEST 2 : Did the Fender Liner Fix Work?

FLEX TEST 2 : Did the Fender Liner Fix Work?
The following morning, Cindy and I headed back down the street to see if my fender liner fix did the trick. As you can see here, we worked our way up the same obstacle and if anything, went high enough to hang a tire.
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So far so good. Time to twist up the other way.
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Just because I thought it's worth noting, what you see here is our Cooper STT Pro squashing out and planting its tread firmly on the rock face below with 29 psi as verified by our TPMS.
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So.... how'd the fender liner fix do you might be asking? Well, here's a shot of the driver side rear and as you can see, the fix worked out great. The tire came close but cleared it without any problems.
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Same is true of the passenger side. As you can see here, it got close but the tire totally cleared.
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Not a mark can be seen, felt or found on the fender liner.
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And there you have it, no more rubbing or none that really matter anyway. Clearly, 37x13.50's mounted on wheels with 4.75" of back spacing can be run with just 2.5" of lift so long as it comes with the right amount of bump stop extensions and your rear fender liners are modified. I hope you found the information on this thread to be helpful. Please let me know if you have any questions. :cool:
 

BillArnett

New member
Great write up, Eddie. Very helpful.

Those springs sure are twisted into pretzels at full compression. Is that really OK?
 

Onlyone

Member
Thank you very much Eddie. This is the exact spot mine was rubbing. I will use this to fix the problem. Thanks for the leg work!
 

JAGS

Member
Dude, that is awesome! Looks fantastic all flexed out too. What a great write up! Are we allowed to ask questions?? LOL.

How would 12.5 tires and more/less BS fare given the tight clearance you saw with 13.5 and 4.75 BS.

29 psi isn’t all that aired down. Just curious what you run the coopers at for street use?

More just a comment, but the slightest trim of the liner edge with a Dremel would all but guarantee no rubbing on rear wheel well. And that means keeping the full liner in tact and the evap covered, which is great.

Like I said, way awesome! Now, how much will things change when you go coil overs?? [emoji6] [emoji23]
 

wayoflife

Administrator
Staff member

wayoflife

Administrator
Staff member
How would 12.5 tires and more/less BS fare given the tight clearance you saw with 13.5 and 4.75 BS.

12.50 would make everything fit even better. They may not even rub in some of the places up front that we were seeing especially if you run them with the same 4.75" of back spacing or more. If you run less back spacing, you will most likely see the same rubbing issue or MORE. It all depends on if you can get your tires to tuck up and under the fenders or not. If not, they will catch the outer edge of the fender trim.

29 psi isn’t all that aired down. Just curious what you run the coopers at for street use?

On Moby and Rubicat, we run 30 psi as street pressure. It's what I aired up JET Li's tires too although I was clearly a pound off. I may start running a bit more assuming I can keep the tread nice and square to the ground still.

Like I said, way awesome! Now, how much will things change when you go coil overs?? [emoji6] [emoji23]

I'll worry about it when I get there :crazyeyes:
 

JAGS

Member
12.50 would make everything fit even better. They may not even rub in some of the places up front that we were seeing especially if you run them with the same 4.75" of back spacing or more. If you run less back spacing, you will most likely see the same rubbing issue or MORE. It all depends on if you can get your tires to tuck up and under the fenders or not. If not, they will catch the outer edge of the fender trim.

So, many of the other beadlocks out there would see some pretty significant issues with stock fenders. A 4.5 BS with 12.5 tires might even have concerns. That’s kind of crazy when you think about how different that is from the JK.


On Moby and Rubicat, we run 30 psi as street pressure. It's what I aired up JET Li's tires too although I was clearly a pound off. I may start running a bit more assuming I can keep the tread nice and square to the ground still.
More PSI is good for MPG assuming you don’t risk tire wear and comfort. Thanks for sharing.


I'll worry about it when I get there :crazyeyes:

Hmm, I’m sure it will happen...and as you say, sooner than later. [emoji12]
 

wayoflife

Administrator
Staff member
So, many of the other beadlocks out there would see some pretty significant issues with stock fenders. A 4.5 BS with 12.5 tires might even have concerns. That’s kind of crazy when you think about how different that is from the JK.

Oh, you could run less backspacing but you'd also need to run more lift. You know that Cindy and I prefer a nice low stance and that's a big part of why we went this route.

More PSI is good for MPG assuming you don’t risk tire wear and comfort. Thanks for sharing.

I'm gonna have to do a chalk test to see how high we can go before we our footprint is no longer square. Granted, our TPMS wants to be aired up to 37 psi just have the warning go off :rolleyes2:
 

Trail Bud

Member
Was looking forward for this test for the jl. Looks like everything works! It looks good twisted up.
Question if you air down to say 12psi. Will you get rubbing?
 

wayoflife

Administrator
Staff member
Awesome that that setup works so well.

Hard to believe that's all that's needed to run 37's :crazyeyes:

Was looking forward for this test for the jl. Looks like everything works! It looks good twisted up.
Question if you air down to say 12psi. Will you get rubbing?

Good question. Had we been running less air, the rub may not have occurred or at least, not as bad. But then, it really didn't take much to address it. :yup:
 

13_gecko_rubi

New member
Those wheels and tires clear pretty much perfectly with that setup and some very slight liner mods. Perfect. I’m with you on removing the bumper end caps. It looks ok on a JK but that look on the JL with the lower body line just didn’t do it for me either!


Sent from my iPad using JL Wrangler Jeep Forum mobile app
 

shotcoach

Member
Awesome write up!

Thanks for doing such a great write up on this! As I'm reading it I'm wondering what kind of liner trimming you're going to do and then you pull out the heat gun! Super cool! :cheesy:
 

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