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Running 37" tires + with stock gearing? experiences???

UKCATS

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So, @MORTON what’s the plan you are making for your Jeep? Looking forward to seeing it.
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TrailTorque

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So, @MORTON what’s the plan you are making for your Jeep? Looking forward to seeing it.
Im not sure yet honestly. I go back and forth and since my wife approved of the Gladiator in the future and keeping the JLU it’s changed my outlook potentially.

I got the JLU to rebuild it axles and all @Sean K. style.

So that is still on the table and going to happen but I need to wait until after I secure the Gladiator.

Right now I’ve just done some minor mods and I’m hoping the itch doesn’t take over because it’s killing me not ripping it apart. It’s turned into my DD so I think it’ll be best to wait for the Gladiator, secure that and then begin ripping the JLU apart so I at least have a DD.
 

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Re gearing to the proper ratio for tire size actually does increase fuel mileage. After over a dozen Wranglers, I know what I’m talking about. This dudes experience is the same.

In the video they didn't claim it to be totally scientific, and considering the 4-month span between tests, there's plenty of room for discrepancy. They also didn't mention how well the odometer was calibrated before each test. My experience hasn't been 10% increase. It's been a wash or decrease. Again, big performance boost on old 4-speeds, but not much to gain with modern 8+ speed transmissions
 

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UKCATS

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In the video they didn't claim it to be totally scientific, and considering the 4-month span between tests, there's plenty of room for discrepancy. They also didn't mention how well the odometer was calibrated before each test. My experience hasn't been 10% increase. It's been a wash or decrease. Again, big performance boost on old 4-speeds, but not much to gain with modern 8+ speed transmissions
Not trying to talk you into regearing. You obviously can do what you want. New guy was asking for firsthand experience, I gave him mine.
 

Toycrusher

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Not trying to talk you into regearing. You obviously can do what you want. New guy was asking for firsthand experience, I gave him mine.
My apologies, It's a Monday, I may be a wee bit too aggressive at the moment... :captain:
 

UKCATS

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jimmyjames82

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thanks for the knowledge fellas!
 

Carlton

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Does anyone here have experience running stock gearing while running 37+ inch tires??

Can you tell me what jeep you had even if it was a previous JK. Did it damage anything? What kind of terrain did you drive on? Length of time/miles? Anything and everything you could tell me about the experience is greatly appreciated!!
Your profile shows that you have a JK and you mention JK in your post.

If you have a JK with 3.21 gearing, do not attempt to run 37" or larger tires. The jeep will be a slug. I drove a JK on 37s that wasn't regeared once. Seriously had to press the pedal halfway to the floor to start moving on flat roads...
 

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jimmyjames82

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Your profile shows that you have a JK and you mention JK in your post.

If you have a JK with 3.21 gearing, do not attempt to run 37" or larger tires. The jeep will be a slug. I drove a JK on 37s that wasn't regeared once. Seriously had to press the pedal halfway to the floor to start moving on flat roads...
i do have a jk with 3.73 diesel 2.8crd. I'm in Korea so we have the euro model. But I have some friends with JL's and the 8 gear trans and was getting opinions from you guys. What I take is, 37''s are fine with the 8 speed and a tazer to adjust the speedo/gear shift timing. it may not be the optimum scenario but it's not detrimental to change the gears.
 

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i do have a jk with 3.73 diesel 2.8crd. I'm in Korea so we have the euro model. But I have some friends with JL's and the 8 gear trans and was getting opinions from you guys. What I take is, 37''s are fine with the 8 speed and a tazer to adjust the speedo/gear shift timing. it may not be the optimum scenario but it's not detrimental to change the gears.
37s will work on an auto JL Rubicon which has 4.10 gears. I wouldn't reccomend it with the Sahara or Sport which have 3.45 gears.

We don't have the JK with diesel in the States. A diesel with 3.73 may work.
 

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I'm not an expert, just wanted to add my personal experience. I have a 2020 Willy's edition JLU that has the 2.0L turbo and the 8 speed automatic and 3.45 gears.

The 2 local off-road shops swore I would have no issues going to 37's, which I found hard to believe, as I thought I'd need to go to 4.88 gears.

After 600 miles on the 3.45 gears and 37s, having done mountain and desert trails, and gone up over 6k in elevation on steep mountain roads, they were right. That transmission, paired with the 2.0L turbo is insane. While there is some very slight loss of power, I am having no issues at this point. It's possible I'm not using 8th gear, but this is something I need to pay closer attention to to see. I'll try and test that and post again.

Will I feel the same way 5k miles from now? Who knows, but for now I have no plans to re-gear. And yes I am just as shocked as you probably are reading this.
 
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OnlyOne

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I'm not an expert, just wanted to add my personal experience. I have a 2020 Willy's edition JLU that has the 2.0L turbo and the 8 speed automatic and 3.45 gears.

The 2 local off-road shops swore I would have no issues going to 37's, which I found hard to believe, as I thought I'd need to go to 4.88 gears.

After 600 miles on the 3.45 gears and 37s, having done mountain and desert trails, and gone up over 6k in elevation on steep mountain roads, they were right. That transmission, paired with the 2.0L turbo is insane. While there is some very slight loss of power, I am having no issues at this point. It's possible I'm not using 8th gear, but this is something I need to pay closer attention to to see. I'll try and test that and post again.

Will I feel the same way 5k miles from now? Who knows, but for now I have no plans to re-gear. And yes I am just as shocked as you probably are reading this.
True, and I agree. I see no reason to re-gear with 37's but the turbo motor is a whole other story. I had a JLUR on 37's with the V6 and with the 8 speed it was fine but you did have to really wind it out to go anywhere, so I can see some people definitely wanting gears. Not so with the turbo.
 

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I have 37/12.5 KM2s and I have lost about .5 to 1 MPG in town which is where I drive mostly and thats corrected for the difference in tire height...power is about the same as stock up to 50ish mph....when you are cruising at highway speed you can feel it working harder and downshifting earlier...hits for more like 2 MPG at 70-75 mph...plenty of passing power and acceleration at speed so thats no difference really when you get on it...just my experience...I am not planning to regear...I want to preserve my factory warranty on my axles until the 8 years is up...I actually put my stock rubicon wheels and tires on for my commute and when I go wheeling 5-6 times a year I throw on my used JK Rubicon Hard Rock wheels with 37s and hit the trail...saves my balljoints and brakes for sure :)
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