37s and questions

[tk30184]

I’ve read tons of threads and I know some folks say 37s and 4.10 are “good enough” depending on what you’re doing with your rig. Mine is a daily driver. It goes on the random forest service road now and again but it won’t get crazy til it gets a lot more miles on it. My round trip to and from work is less than 5 miles so I’m fine with my pavement princess status for now.
That said I’ve considered several different things. I intend to keep my rig for many years so I’m thinking long term.
I’m running 37s with 4.10 gears. I’m actually very surprised at the performance. I’m not afraid to pull out in traffic but I can see what people are talking about when “chasing” gears and such. So here’s what I’m thinking. If there are other better options, please let me know.
1. Keep the 4.10 gears and go down to 35 inch tires. I’ve heard that 4.10 is the sweet spot for 35s and I’ve heard that 4.56 is the only way to go.
2. Re-gear to 4.88 and forever run the 37s
3. Re-gear to 4.56 and run 35s or 37s depending on whichever feels best.
4. While I was thinking about all of this I suppose I could just get a Tazer or something like it and jack around with the shift points and see what that does?
When I chose to drive a Jeep I decided
mpg is not something I can worry about so any points on that for me are pretty moot.
So… my favorite idea is to re-gear to 4.88 and forever run the 37s. If I do that and do the necessary programming I’m pretty sure since my drive to work is so short I’ll be pretty happy, but what about the weekend road trips or a long drive to the beach? I accept my mpg will suck even with a marginal improvement, but will I be screaming down the highway at 2500 rpm in 8th gear at 70? Will my 3.6 and drivetrain handle that okay?

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[kah.mun.rah]

Once you have 37s it will be difficult to go back to 35s. It's like deciding to put a smaller T.V. in your living room and expecting to be just as happy with the view. 4.88 is a good idea with 37s and runs well around town, on the highway, and off-road. That said, here is a graph I made showing the difference between 4.10 and 4.88 with 37s. Big difference in the shifting but it was interesting to see that the 0-60 time didn't change. The reason you start to see 8th gear again is probably because it is shifting through 1-7 quicker with the 4.88 ratio. I'm no transmission expert but this graph makes me think that the 4.88 pattern is healthier on your transmission too. Another bonus is the 4.88 will change your crawl ratio from 85.9:1 to 91.9:1 if you decide to get into rock crawling.

 

[lowmpg]

4.88's, 37's, get a Tazer cause you need to square away your tires and gears - or else all of this was pointless.

You can run 37s with 4.10s, but it is a night and day difference when you got to 4.88

 

[gato]

What engine? What transmission? What 37s? What altitude do you drive in? 2dr or 4 dr? Heavy or light build?

If you have a 3.6, MT in Denver you'd want 488 just to turn the 33s.

If you have the 2.0/ZF8 and super light 37s (like KO2s) at sea level you'd be more than happy with 4.10s.

The weight difference between a super light 37x11.5 and a super heavy 37x13.5 alone would justify two gear size jumps.

"What gear for 37s?" is a completely meaningless question without the details.

It's like asking what is the best ammo for hunting? Hunting what? Criminals? Pheasant? Elephants?

 

[kah.mun.rah]

What engine? What transmission? What 37s? What altitude do you drive in? 2dr or 4 dr? Heavy or light build?

If you have a 3.6, MT in Denver you'd want 488 just to turn the 33s.

If you have the 2.0/ZF8 and super light 37s (like KO2s) at sea level you'd be more than happy with 4.10s.

The weight difference between a super light 37x11.5 and a super heavy 37x13.5 alone would justify two gear size jumps.

"What gear for 37s?" is a completely meaningless question without the details.

It's like asking what is the best ammo for hunting? Hunting what? Criminals? Pheasant? Elephants?

Great points. He mentioned 8th gear so I am assuming AT.

 

[Whistle Pig]

I have a 2020 JLUR with a 2.0L, 3.5" Clayton lift and 37x12.50 17 Nitto Trail Grapplers on Mickey Thompson Classic wheels. When I lifted and bolted the tire and wheel package up on the stock 4.10 gears, it struggled. Western Kansas flat runs it struggled to get in 7th gear and when it did it wouldn't hold it very long and it would shift down to 6th. I knew regearing was going to have to happen when I built the Jeep and I ended up going with 4:88 just for highway use and I am still on the D44's. I see 8th gear pretty frequently with 4:88. I almost went with 5:13 but the D44, the pinion gets really small when you get into the 5's on gearing. IMO, if you are going into the 5's you just as well go 1 tons to get more meat on the bone on the gear sets and I say that if you plan to wheel it offroad.

As I am set up now, I can get 20 mpg at 70 mph if there is no head or cross winds. If I am bucking a head wind (30 mph) it'll still get 13 mpg. Do I care? No, it's a brick that has the aerodynamics of a cow. The Nitto's are heavy and there are many other tires in a 37 that are considerably lighter but my Jeep spends alot of time in the rocks so I wanted a tough reliable tire and the Nitto is but it's heavy. 4:10s and 37's, it will work but you have to go with the cheaper tires that are light in weight to make it work.

 

[The Fixer]

What engine? What transmission? What 37s? What altitude do you drive in? 2dr or 4 dr? Heavy or light build?

If you have a 3.6, MT in Denver you'd want 488 just to turn the 33s.

If you have the 2.0/ZF8 and super light 37s (like KO2s) at sea level you'd be more than happy with 4.10s.

The weight difference between a super light 37x11.5 and a super heavy 37x13.5 alone would justify two gear size jumps.

"What gear for 37s?" is a completely meaningless question without the details.

It's like asking what is the best ammo for hunting? Hunting what? Criminals? Pheasant? Elephants?

Good points! My son has been driving his JLUR on Cooper Discoverer AT 37's for the last year with the 3.6, auto, and stock 4.10s. We used JScan for speedo correction. We're on the East Coast, so mostly sea level or slightly above. His experience so far is positive. His daily commute is almost 50 miles round trip, mostly highway, and a lot of traffic, so the fuel mileage calculator in the dash says it's in the 17's. He also drove it down to Daytona from NJ for Jeep Beach and the fuel mileage according to the cluster was in the mid-19 mpg range for the trip. He has wheeled it a few times as well.

All in all, I think because we're at sea level it's not as big of a deal. I know many owners report needing to regear, especially in other parts of the country that are way above us.

 

[KHR Racing]

5.13 and you will be very happy…..

 

[yokramer]

Do you WANT want 37s? If so put them on with your 4.10s and see how it goes, if its bad put 4.88s in it.

 

[jadmt]

as many times as i had read that 37's and 4.10's would be a bad mix I thought for sure I would need to re-gear but that has not been the case..I live in Montana and do a lot of trips to moab etc and daily drive my jeep. after 6000 or 7000 miles I don't even think about it. accelerates great, offroads great and sees 7th and 8th and does not hunt for gears and I am getting good mpg on the highway. I switch back and forth between 37's and 35's and there is no real difference in how it feels seat of the pants. my tranny temps are the same with either set on under the same conditions. my last trip to moab traveling with my buddy who has the exact same build and tires except he has a 2.0 and 4.56's we got essentially the same mpg as we of course filled up at the same time. missoula to moab has lots of up and downs and lots of wind. try it and decide.

 

[bmpcamry09]

Just a heads up, you can't change shift points with JScan, you can only program the computer to correct the speedo. Which will give a sensation that your shift points are better, but it just seems that way because your speedo is correct, the TCM is still commanding the shift at the same output shaft speed (which is your driveshaft speed). On this platform with the 8 speed, there is no correlation between your speedo being accurate and the transmission deciding when to shift either, this is a false statement made by multiple people on this and other forums. Shift RPM differenes are simply because of the regearing and not something that will change with settings in Jscan.

I've tuned a bunch of these now ranging from 31.5s on 3.45s to 40s on 5.38s. For 37s, 4.88s seem to make everyone the happiest, but 4.10s are tolerable with good engine and transmission tuning. I've got two customers running 40s paired with 5.38s and they love it.

 

[CaddyshackGopher]

I ran BFG KO2 35's E-Rated (a bit heavier but BFG run small) w/ my 4.10's for approx 40K miles. It was fine. I put on 37" MT Baja Boss A/T w/ my factory 4.10's and tested it out for a month. To me it was noticeably sluggish and 8th gear was completely gone. This week I just finished my 500-mile break-in period w/ 5.13 gears (Revolution REM finished). Power off the line feels better than when I drove it off the lot brand new w/ the 285's and 4.10. I see 8th gear on the highway against headwind now.

 

[embedded rock]

I always like reading these threads of gears and 35/37in tires. Going into my second JL, I'm debating the Xtreme pkg with 4.56 or regearing to 4.88. New or used? There are used JLR's where I would encounter a regear expense. Used JLR's with Xtreme are not really out there; so, the new JLR with Extreme is an option.

My former JLUW with Xtreme tells me to go JLR with Xtreme 4.56 for 35's and 37's knowing that the JLR 4:1 TC, 4.56, and 37's would be good--no intention of trails like Pritchet, but more (5-7's) than those 3-5 trails I ran in Moab the past couple of years.

 

[kah.mun.rah]

For those telling him to try the 37s with his 4.10, he said that he is currently running 37s if you read his 2nd paragraph.

 

[lowmpg]

For those telling him to try the 37s with his 4.10, he said that he is currently running 37s if you read his 2nd paragraph.

reading is hard, and more so it is people with 4.10's running 37s convincing themselves that is a good combo

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