35" vs 37" - Need some advice!

[Turniipp]

I have a '21 JLURD and am finally doing a Clayton 2.5" lift and will be putting new rims and tires on it. At one of the shops the tech asked why not throw 37's on it, and claimed not only would they fit without rubbing, but that they wouldn't throw off geometry or add any other issues.

I've been researching like crazy since then, and basically believe the following: 37's would fit and I don't believe it would cause geometry issues or any other major issues, however I've read plenty that state that axles should be trussed and knuckles should be cast iron and hydro-steer installed and so on and so forth.

So, what have you done and what would you do differently?

This is my dream vehicle and I've been saving my pennies to build it correctly, so I'm not as concerned about cost as I am dealing with issues later because I didn't do it right the first time. Any help would be mightily appreciated!

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[CableDaddy]

I have a '21 JLURD and am finally doing a Clayton 2.5" lift and will be putting new rims and tires on it. At one of the shops the tech asked why not throw 37's on it, and claimed not only would they fit without rubbing, but that they wouldn't throw off geometry or add any other issues.

I've been researching like crazy since then, and basically believe the following: 37's would fit and I don't believe it would cause geometry issues or any other major issues, however I've read plenty that state that axles should be trussed and knuckles should be cast iron and hydro-steer installed and so on and so forth.

So, what have you done and what would you do differently?

This is my dream vehicle and I've been saving my pennies to build it correctly, so I'm not as concerned about cost as I am dealing with issues later because I didn't do it right the first time. Any help would be mightily appreciated!

fellow JLURD.

A 2.5 will definitely fit 37s, and IMHO is a better fit for the 4dr. That breakover angle is no joke. Every inch helps.

No, you don’t need a truss but the extra strength certainly can’t hurt!

iron knuckles can certainly help. Knuckles like Reids are much stronger, and the added forces that larger wheels intrinsically add will push the stock aluminum ones much harder. Will they break? Honestly.. maybe, maybe not. Depends on how you wheel/drive/etc. But I haven’t honestly seen anything that says they are *required* out the gate. But, and this is my opinion again.. I think it’s telling that Jeep makes some JL’s with steel knuckles. They wouldn’t do so without some reason.

You don’t need hydro assist. But is pretty great. 37s can be unforgiving to turn on the rocks and hydro can absolutely help with that. Also.. it’s very very difficult to get death wobble with hydro. It’s powered.. and unless you’ve got some seriously loose parts.. the best you’ll see is an uncomfortable shimmy.

Now, for what I did. I did a 4.5 inch lift, 37s, a front truss and gussets, Reid knuckles, and hydro assist.

I did the 4.5 because it helps negate big rocks and breakover angle difficulties.

I did 37s because bigger wheels also do the same as above *and* personally I think the 4dr looks so much better with 37s. And I knew the diesel would laugh at the extra load.

I did the truss and gussets because the FAD makes me nervous and past experience with a JK makes me nervous with tubes and upper and lower C’s beginning to bend.

I did the Reid knuckles because my steering wasn’t as solid feeling as I wanted and I thought the Reid’s might tighten it up. It did a little bit. And I can trust the iron faaaaar more. Jeep certainly seems to considering, again, some JLs come with steel instead.

and I went with hydro because I’ve shattered a sector shaft (‘12 JK on 35s) and boy that fight sucked. With hydro that is empirically less likely, and the “fight” required to steer on trail is easier. And I knew with 37s that fight would be harder than my old JK.

 

[Turniipp]

@CableDaddy did the 4.5" lift require new drive shafts?

Also, did the 37's require you to regear, or does the diesel even notice them?

 

[CableDaddy]

@CableDaddy did the 4.5" lift require new drive shafts?

Also, did the 37's require you to regear, or does the diesel even notice them?

yes, the 4.5 required a new front driveshaft but the rear is still fine… until I can afford to replace it haha. I think the cut-off for the front driveshaft is 3 or 3.5 inches.

i haven’t regeared yet but I want to. I did notice a difference but it’s not that large. Going to 37s, to match stock “feel” I would need 4.10s. That’s only one “step” up. Not a big deal. Still have torque for days (big note, just incase you didn’t know: when going into 4L the auto with your diesel shifts into 2nd gear, not 1st, unlike the 2.0 or 3.6). However.. as I intend to only use my diesel for off-roading.. I’m going to go with 4.56s. Going up the mountainside angers the transmission if you don’t regear, from what I can tell. Went into limp mode so now I just go up slow and steady (at or within 5-10mph below) and it hasn’t caused me an issue since.

 

[Grayhound]

Why are we not posting pics with our comments? Everyone want to see a diesel on 37s!

I went 35s because I wasn’t ready for a lift and rims. I agree 37s seem to be the sweet spot. I lost a couple mpg just moving to 35s but don’t feel it in the pedal at all.

 

[BDinTX]

2.5” lift, went to 37”s and they rub the fender liners when off-road. This is after adding 1/2” of front bump (diesels start with 1-3/8” more front bump to begin with). Rear also rubs with 2” of added bump.

Live in TX (low altitude,hot), see 8th gear often enough, can get ~22mpg on freeway with cruise set a few miles under the 75 limit. Have not regeared, don’t plan to.

You’ll need to an aftermarket spare tire carrier to clear the bumper unless you’re one for doing a spare delete.

Video of tire rub:


Edit: things I’d do differently plan to add another 1/2” of bump front and rear. Should have gotten Teraflex hinge gate AND carrier (on right) instead of just the carrier. Plan to add the hinges (on left) soon.

 

[CableDaddy]

Why are we not posting pics with our comments? Everyone want to see a diesel on 37s!

You are absolutely correct. How dare I err in such a blasphemous way!

I went 35s because I wasn’t ready for a lift and rims. I agree 37s seem to be the sweet spot. I lost a couple mpg just moving to 35s but don’t feel it in the pedal at all.

I lost more than a few going to 37s. Regearing would help, but as I want to go 4.56s, that might cost more than I gain. Either way, I won’t be regearing for quite a while.. unless I feel I *need* it.

 

[Turniipp]

Should have gotten Teraflex hinge gate AND carrier (on right) instead of just the carrier. Plan to add the hinges (on left) soon.

Is that a Mopar tailgate reinforcement I see? Is it a matter of form or function? Have you upgraded your steering yet on 37's?

 

[Ryan long]

Why are we not posting pics with our comments? Everyone want to see a diesel on 37s!

I went 35s because I wasn’t ready for a lift and rims. I agree 37s seem to be the sweet spot. I lost a couple mpg just moving to 35s but don’t feel it in the pedal at all.

[/QUOTE

I have a '21 JLURD and am finally doing a Clayton 2.5" lift and will be putting new rims and tires on it. At one of the shops the tech asked why not throw 37's on it, and claimed not only would they fit without rubbing, but that they wouldn't throw off geometry or add any other issues.

I've been researching like crazy since then, and basically believe the following: 37's would fit and I don't believe it would cause geometry issues or any other major issues, however I've read plenty that state that axles should be trussed and knuckles should be cast iron and hydro-steer installed and so on and so forth.

So, what have you done and what would you do differently?

This is my dream vehicle and I've been saving my pennies to build it correctly, so I'm not as concerned about cost as I am dealing with issues later because I didn't do it right the first time. Any help would be mightily appreciated!

i have stock axles on my diesel with 37’s with 3.5 metalcloak lift. 2.5” will clear and that diesel barely noticed the 37’s. Put your 37’s on and recalibrate your speedo and you’ll be fine. I just drove from California to Idaho over quite a few mountain passes and was in 8th gear almost all the time. I love my diesel. 5k oil changes and use a fuel additive. I use hot shot EDT on all my diesel’s

 

[autotragic]

I have a '21 JLURD and am finally doing a Clayton 2.5" lift and will be putting new rims and tires on it. At one of the shops the tech asked why not throw 37's on it, and claimed not only would they fit without rubbing, but that they wouldn't throw off geometry or add any other issues.

I've been researching like crazy since then, and basically believe the following: 37's would fit and I don't believe it would cause geometry issues or any other major issues, however I've read plenty that state that axles should be trussed and knuckles should be cast iron and hydro-steer installed and so on and so forth.

So, what have you done and what would you do differently?

This is my dream vehicle and I've been saving my pennies to build it correctly, so I'm not as concerned about cost as I am dealing with issues later because I didn't do it right the first time. Any help would be mightily appreciated!

Unless you need to fit in the garage then you might want to double check clearance before you just jump straight to 37s. Otherwise the tires will fit fine with that lift.

 

[Grayhound]

How!? Are you tuned? Going downhill all the time? How are you getting this kind of mileage?

 

[Mocopo]

On my recent wheeling trip, the guy I went with and I both had 37s. There was a noticeable difference with the ease of his steering with hydro assist, opposed to my stock steering. Still, reasons I didn't upgrade anything to go to 37s... I got the XR package. That means a Dana HD 44 up front, which has a thicker axle tubing and steel knuckles from the factory. Stock 4:56 gears. The bumpstops it came with were practicality made for 37s. Also the mopar tailgate reinforcement. These are all things I would have considered upgrading if it didn't come upgraded from a standard Rubi already.

That being said, people throw 37s on JLs without those upgrades and wheel them all day long.

 

[SadRobot]

Not sure if this helps but I don't think anyone has gone 37s and regretted it.

 

[Ryan long]

How!? Are you tuned? Going downhill all the time? How are you getting this kind of mileage?

I don’t know. It doesn’t use much def either. I drive fast everywhere I go. 85 mph through Nevada and I was getting 22 mpg

 

[Ryan long]

I don’t know. It doesn’t use much def either. I drive fast everywhere I go. 85 mph through Nevada and I was getting 22 mpg

I bought it new. It’s not tuned. I recalibrated the Speedo and muffler delete that’s it

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