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2.0 on 37's with 4:10 gears in a JLUR

JLU_rubi18!

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I have had a number lifted trucks with oversized tires and reprogramming the ECU for the correct tire diameter will make the biggest difference in your overall performance. Yes, the JL does have an 8-sped auto and I have had a RAM 1500 with this transmission. The difference in tire diameter and actually speed is what really hurts the performance when you make the leap up to a 37” from a stock 32.5” stock tire. Once I’ve had the ECM “flashed” or added a programmer that allows tire diameter correction, this brings the vehicle back into its desired operating range. In actuality you should re-gear to a 4:88 or 5:13 gears for 37’s, but reprogramming the ECU for the correction in tire diameter would be the first step to get the engine back into it’s ideal operating range. I had Silverado on 35”s with a 6-spd auto and 3:73 gears, once I added the programmer and corrected for tire diameter, it was night and day difference. Ideally I should have re-geared to 4:10’s, but I never skipped a beat after the ECU was re-programmed. I wheeled that truck in the desert for 5 years with no issues?

...just my 2 cents? :beer:
Regearing to 5.13 ( unless 40s )will be way too much gear for this platform. Those were gearset numbers for the JK platform and no longer apply to the 8 spd. The only thing flashing the computer does is change your speedo and your shift points to accommodate for the new fire diameter. It will help butnthe only way to truly add power back is through a regear. Personally I’m going to see how these stock axles do with 4.10s. Based on my experience with the JK 3.6 and auto I’m betting this handles 35-37s very well.
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JLU_rubi18!

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Maybe now with no problems, personally I think you're crazy to go 40's without re-gearing, not a good idea.
You lose 7th a s 8th bear on the hwy. but you still have 6th turning 2800 rpms or so. How’s that different from 37s on 4.10d on a JKU 5spd which many people did and so did I? It’s actually not as bad as you think.
 

Zandcwhite

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Maybe now with no problems, personally I think you're crazy to go 40's without re-gearing, not a good idea.
You would literally need 5.38 gears in a late model jk in order to match the 1st gear final drive ratio of a JL with stock 4.10's. An early jk with an auto would need 6.78 gears. The 8 speed transmission is a game changer. The overdrive gear in a jk was the same as our 7th gear. With the 5.38's required to match our 1st gear puts the jk at the same rpm as a jl with 4.10's in 6th gear. Why sacrifice top end gearing for bottom end you don't need?
 

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SG19JLUR

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I just put 37's on mine last week and it handles it fine with stock 4.10 gears. I still see 8th gear regularly and it will even hold 8th up mild hills. I also don't find that I'm missing anything down low...it still accelerates just fine. I could see maybe regearing to 4.56 or 4.88 but honestly it's at the very bottom of my list.
 

BDinTX

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I just put 37's on mine last week and it handles it fine with stock 4.10 gears. I still see 8th gear regularly and it will even hold 8th up mild hills. I also don't find that I'm missing anything down low...it still accelerates just fine. I could see maybe regearing to 4.56 or 4.88 but honestly it's at the very bottom of my list.
Is yours a 2.0 liter? We're going to 35's, I'd love 37s but concerned we'll lose too much low end acceleration and torque.
 

SG19JLUR

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Is yours a 2.0 liter? We're going to 35's, I'd love 37s but concerned we'll lose too much low end acceleration and torque.
Yes, mine is a 2.0 with 8-speed. It's a '21 without e-torque if that makes a difference. It came with 33's (obviously) and within a week I changed to 35's. I don't really think I noticed a bit of a difference changing to 35's. I ran the 35's for about a month and then changed again to 37's. I barely notice a difference going from 35's to 37's, but if I went from 33's to 37's it probably would have been more noticeable. I definitely don't regret going to 37's, and if anything I would spend money on a tuner or performance mods before regearing.
 

BDinTX

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Yes, mine is a 2.0 with 8-speed. It's a '21 without e-torque if that makes a difference. It came with 33's (obviously) and within a week I changed to 35's. I don't really think I noticed a bit of a difference changing to 35's. I ran the 35's for about a month and then changed again to 37's. I barely notice a difference going from 35's to 37's, but if I went from 33's to 37's it probably would have been more noticeable. I definitely don't regret going to 37's, and if anything I would spend money on a tuner or performance mods before regearing.
Ok cool thanks for that insight. I'm getting a device to recalibrate for tire size and TPMS but wasn't planning on getting a tuner.
 

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SG19JLUR

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Ok cool thanks for that insight. I'm getting a device to recalibrate for tire size and TPMS but wasn't planning on getting a tuner.
Correcting the speedo is a must to get your shift points calibrated properly. I use a Tazer Mini but I know there are other devices that can do it too. I'm not suggesting that you NEED a tuner, I'm just saying I would rather spend $2k on an intake, exhaust, and a tune (Superchips claims +60hp/90tq) vs. $2k (parts and labor) on new gears.
 

NewbieJon

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Yes, mine is a 2.0 with 8-speed. It's a '21 without e-torque if that makes a difference. It came with 33's (obviously) and within a week I changed to 35's. I don't really think I noticed a bit of a difference changing to 35's. I ran the 35's for about a month and then changed again to 37's. I barely notice a difference going from 35's to 37's, but if I went from 33's to 37's it probably would have been more noticeable. I definitely don't regret going to 37's, and if anything I would spend money on a tuner or performance mods before regearing.
Have you been crawling with your rig? I'd like to know if turbo lag and the subsequent surge is a problem when crawling over obstacles.

Trying to finalize my engine choice for my first Jeep purchase. It's between the 2021 V6 with eTorque and the turbo 4 without eTorque. I plan on a lot of low speed technical stuff, and I want the best engine for that. Both engines are fine everywhere else.
 

Zandcwhite

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Snapped a picture on the drive to death valley for reference, cruise control set at 82 mph holds 8th gear no problem and is just under 2k rpms. 37's and stock 4.10's are a great combination for long road trips. With the 4.7-1 1st gear and 4-1 transfer case crawling isn't an issue. There's a slight turbo lag off idle and then there's plenty of torque and gearing for crawling up any obstacles we've pointed the jeep at.

Jeep Wrangler JL 2.0 on 37's with 4:10 gears in a JLUR 20210319_114443
 

SG19JLUR

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Have you been crawling with your rig? I'd like to know if turbo lag and the subsequent surge is a problem when crawling over obstacles.

Trying to finalize my engine choice for my first Jeep purchase. It's between the 2021 V6 with eTorque and the turbo 4 without eTorque. I plan on a lot of low speed technical stuff, and I want the best engine for that. Both engines are fine everywhere else.
I haven’t been on anything super technical yet but I went on some trails this afternoon. There were some pretty steep and rocky sections and I never felt like I needed lower gearing. I also drove through the mountains to get here and I had absolutely zero issues going uphill. At this point I think someone would have to offer me a free set of gears for me to have any desire to change them.



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