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37’s, 3.0, and 3.73’s

Bravo

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Ok question for the gear heads... 2020 wrangler with the eco diesel... just put a lift and 37’s under it... Jeep has less than 500 miles on it... strong acceleration before the lift and tires and still pulls like crazy after... hardly notice any difference at all with the new tires... adjusted shift points and speedo with JL tazer...

would u spend the money to get back close to stock with 4.11’s, leave it alone, or possibly drop 4.56’s in it and possibly give it too much gear for the diesel?

Bravo

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GearWhore

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I am very interested to see what you do here! Ready to move from the Trailhawk diesel to the JLUR diesel with 37's. The WK2 dropped ~2-3 mpg moving from 30.5" to 32" tires, though only slightly noticeable drop in acceleration. The additional weight was noticeable, and I found the same when I drove a JLUR diesel last week. 500 lbs! That and the rotational mass of 37"+ tires makes me think the regear would happen before too long, probably to the 4.11. Regain some of the super-low crawl, probably some fuel mileage, and less strain on the drivetrain. Maybe?

Great looking JL!
 
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Bravo

Bravo

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Thanks man... I’m thinking the same as far 4.11’s but I’m still feeling it out as I’ve put roughly a 100 miles on it since I installed the tires...
 

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Give it a year...or an axle shaft. See if you still think it would be beneficial then. Or do it now so I have feedback before doing mine. ;)
 
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Bravo

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It’ll probably happen soon...
 

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I just went with 4.56 and I think I’m regretting it already. I was hoping it could bring me back to stock feel and with all the added weight that everything will balance out — hopefully gain some MPG.
I was averaging 20-21 mpg with 3.73.
After the regear it dropped to 17 mpg?!
I actually get 17 once I get off the freeway and do city driving… highway is like 15-16mpg. I don’t know, I’m still in the 500 mile break-in period but I’m not liking the numbers already.
The Jeep definitely pulls like or better than stock though.
Jeep Wrangler JL 37’s, 3.0, and 3.73’s 83C8F23E-ADEA-4210-A3E7-85CCC1F5A0D3
 

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I just went with 4.56 and I think I’m regretting it already. I was hoping it could bring me back to stock feel and with all the added weight that everything will balance out — hopefully gain some MPG.
I was averaging 20-21 mpg with 3.73.
After the regear it dropped to 17 mpg?!
I actually get 17 once I get off the freeway and do city driving… highway is like 15-16mpg. I don’t know, I’m still in the 500 mile break-in period but I’m not liking the numbers already.
The Jeep definitely pulls like or better than stock though.
Your mileage should definitely come up 1-2 mpg over the next 5000-10000 miles. This winter I'm getting 21-23 mpg with a large Yakima ski box on the roof. My MPG comes up about 2 mpg without the box; I'd imagine yours would improve similarly without the tent & light bar.

Thanks for your regear feedback!
 

JeepVT

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I wouldn't mind a bit more ooomph, but not for the $$ to go to 4.10s. Plus my 37 KM3s are both smaller and lighter than something like a Nitto or Cooper mud. I'm around 25hwy, 21 town
 

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I just noticed my first posts here were a few months before my late-September 2020 delivery. I'm now up to 20k miles, with probably 5k+ of that off pavement and hundreds of miles of "trail."

@Bravo did you end up regearing?

I haven't regeared, and now not sure I would. At least on the 37s. Maybe twice rock crawling I've thought it would be nice to have lower gearing, but the engine never failed to keep pulling. I am still in 8th gear almost always on highways over 60 mph. Still plenty of get-up-and-go from stoplights, on-ramps, passing, etc..
 

deoenrico

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Your mileage should definitely come up 1-2 mpg over the next 5000-10000 miles. This winter I'm getting 21-23 mpg with a large Yakima ski box on the roof. My MPG comes up about 2 mpg without the box; I'd imagine yours would improve similarly without the tent & light bar.

Thanks for your regear feedback!
I had a chat with the shop who did the gears replacement. The feedback they've been getting from owners who have the same setup (37s and ecodiesel) is that they're getting 26 MPG.
I'm getting 15-16mpg going 70mph... thats no bueno.
I scanned the jeep ECUs and found that my PCM is out-of-date, and my ACC aslo which I use a lot. I'm going to upload the new firmware and will circle back.

Jeep Wrangler JL 37’s, 3.0, and 3.73’s 1
 

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I reflashed/updated the PCM firmware and the rest of the ECUs that were outdated. No DTCs were present.
Here's what I got cruising at 65mph vs 70mph on a flat terrain -- note the "current mpg".

I don't know, maybe this is it... or maybe I'm totally missing something.

Jeep Wrangler JL 37’s, 3.0, and 3.73’s IMG_6636

Jeep Wrangler JL 37’s, 3.0, and 3.73’s IMG_6639
 

word302

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I reflashed/updated the PCM firmware and the rest of the ECUs that were outdated. No DTCs were present.
Here's what I got cruising at 65mph vs 70mph on a flat terrain -- note the "current mpg".

I don't know, maybe this is it... or maybe I'm totally missing something.

Jeep Wrangler JL 37’s, 3.0, and 3.73’s IMG_6639

Jeep Wrangler JL 37’s, 3.0, and 3.73’s IMG_6639
You're driving a lunchbox. You aren't going to get great MPGs at 70.
 

GearWhore

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Didn't realize you already had 28k miles! Now I see you meant you only had ~500 miles on the gears, not the Jeep as a whole.

I can see your mileage though, especially with the tent & lights up there. With the added weight and wind resistance... Still sucks to regear and drop like that. How often do you use the tent? Do you have a way to easily remove and store it when not in use?

My old Cherokee (rolled in the photo) had 3.55 when I bought it. After lifting and adding 31" Thornbirds I regeared to 4.56. Too low for what I was doing and where I was living at the time, but live and learn (expensive lessons) I guess. Was still a fun party trick to get out and walk/stand beside it in first gear.
 

deoenrico

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Didn't realize you already had 28k miles! Now I see you meant you only had ~500 miles on the gears, not the Jeep as a whole.

I can see your mileage though, especially with the tent & lights up there. With the added weight and wind resistance... Still sucks to regear and drop like that. How often do you use the tent? Do you have a way to easily remove and store it when not in use?

My old Cherokee (rolled in the photo) had 3.55 when I bought it. After lifting and adding 31" Thornbirds I regeared to 4.56. Too low for what I was doing and where I was living at the time, but live and learn (expensive lessons) I guess. Was still a fun party trick to get out and walk/stand beside it in first gear.
I use the tent quite often and I do want to know what my MPG would look like with everything installed.
I actually found the culprit. The shop that did the gears programmed an incorrect tire size -- instead of a 37" tire, they put a ~34". I corrected it, verified tire size + vehicle speed using Waze and it is now on point, no more +/- in mph. Here's what I get if im going 70mph at 2000 rpm... 21-22mpg. I guess this isn't too bad...
Jeep Wrangler JL 37’s, 3.0, and 3.73’s Image from iOS
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