Regearing for 37s?

mgroeger

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2020 JLUR w 3.6 Here. Daily drive and wheel as much as I can.

Had 37x13.5r17 Cooper STT Pros...drove them for a week, took them off and went with 35x12.5r17 KO2s.

All the engines in the JL have enough power to run them, but even with 4:10s you can hear a definite change in the work the trans is doing. It’s clearly working harder to get those big monsters spinning. Do I think this work will affect the longevity, no? I think it’s just going to hit you in the wallet in terms of MPG. More time at higher RPMs.

I took mine off because I really don’t want to regear it yet. I think it is a must to run the setup right and be happy with it. Your Jeep looks pretty bare in terms of mods. If you intended to add bumpers, winches, racks, armor, etc, it would be essential just because of the load you are putting in the vehicle.

I think it is about your core philosophy of how/why you run your rig. I would never run 22” rims because they don’t have enough sidewall for aired down wheeling. I want my Jeep to be the epitome of dependable and capable wherever I take it. So I make my choices based on that. As long as you’re willing to pay to put gas in it and are happy with the way it drives/sounds/looks, do whatever. I doubt there will be long term mechanical ramifications as direct result of running them.

Just wasn’t for me w/o a regear. They do look amazing though (37s in general, not yours).

Also, you did seem a a bit sensitive about your decision to put 22s on your Jeep. I think pretty much anytime someone has to defend their choices in advance, they are sensitive regarding the subject.
I think you are my long lost brother.





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Unix_Gawd

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Thanks! Super helpful!
You will also need a FlashCal or something similar to sync the drivetrain, tires, etc. They aren't very expensive and well worth it after dropping alot of green backs on re-gearing. My gears cost $2k, 5.13 Spicers installed by Maxxed Performance in Baytown, Tx.
 

LUV2JEEP

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I did 5.13s with 38" C rated tires. I wish I went ahead and did 5.38s. I use all 8 gears but it takes only a slight hill and it has to downshift. I was originally worried 5.38s were weaker but I called DANA and they said 5.38s are just as strong as 5.13s. Don't be afraid to go higher in the gear ratio!!

Update: I also called Yukon Gear and they basically said the same thing. 5.38 is not weaker. Head is smaller, but the head size is no smaller than the pinion shaft diameter so the pinion is not the weak link (I'm only repeated what I was told). He said the pinion head on the JKs was actually smaller than the pinion shaft and so it would break. Anyway I wish I went ahead and did 5.38s. Those gears were actually in stock at the time and I painfully waited for 5.13s. On a naturally aspirated engine 100 rpm isn't really a lot. I wish I could bump up the rpm maybe 200 and then 8th gear would stay locked in better. Lately I have been getting on the highway and once 8th gear is engaged, I pull the shifter over to lock it into 8th gear (M8). There is no point in having the transmission shift every hill.

Update 2: I decided to help the transmission, my fuel mileage and my ability to tow by dropping tire size down from 38x13.5 to 37x12.5. I'm towing 3500lb RV and thought 38" was too big.
 
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OrangeRuby

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It was just really low on my priority list when balanced with everything else I want to do. I am more into “overlanding” than anything and we haven’t met anything so far we couldn’t accomplish with 35s (probably even 33s on the Jl rubi). You could drop a grand or two every time you turn around with this thing.

Again, my Jeeping philosophy aligns with function far before form when my wallet can’t get both at the same time.
 

ChattVol

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It was just really low on my priority list when balanced with everything else I want to do. I am more into “overlanding” than anything and we haven’t met anything so far we couldn’t accomplish with 35s (probably even 33s on the Jl rubi). You could drop a grand or two every time you turn around with this thing.

Again, my Jeeping philosophy aligns with function far before form when my wallet can’t get both at the same time.
Going to a 37/13.50/17 stt pro load e is a stiff/heavier 37 for a daily driver. Did you consider looking at a lighter 37 that is 12.5" wide and not load e?
 
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fireleo710

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enough about the 22's, your jeep looks great and I'm sure so is everybody's jeep. Mall crawling would not be a problem, but like some others have mentioned, you'll have to upgrade if you do any moderate off roading. Have fun be safe!!
 

OrangeRuby

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Going to a 37/13.50/17 stt pro load e is a stiff/heavier 37 for a daily driver. Did you consider looking at a lighter 37 that is 12.5" wide and not load e?
I got a ridiculously good deal on that set of tires, like $200/tire before tax. A guy ordered them at my local shop and then backed out of the deal. That’s why I went with them (plus I really believe they are good tires.)

I looked at the weights and several other 37s, talked to several of my local Jeep buddies with JL/JT setups, talked with the accessory guy from my dealership. I rode in several other JLs with 37s. There’s no doubt in my mind that the JL Rubi can spin them and be fine. At the end of the day, I feel like it adds some additional strain to the transmission, and, without regearing, isn’t worth the 1” of clearance. The transmission was designed to see all 8 gears on the road. Everyone with 37s and any amount of lift all but loses the 8th gear unless going downhill, and 7th unless flat and no wind.

My position wouldn’t be different even if I only drove my Jeep for wheeling/overlanding and nothing else. Of course if that was all I did, I would just put the 37s on with new gears and a crazier amount of lift/travel.
 

fjwagner

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Nope. My reading comprehension is just fine. But, when you post in a open forum, don’t think you are shielded from other people’s opinions. Plus, the attitude on your first post was a little grating. Enjoy getting laughed at by other Jeepers.
Agreed!
 

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