JTRD on 37" what ratio 4:56 or 4:88

[yrwins]

EAV and the Dealer "MOPAR" is using 4:56. why they (EAV & Mopar) are not using 4:88 ? and the other hand I call Yukon and it tell me to used 4:88
and also don't forget about 4:11
I will not ever go to 40"

I am on the process of install Mopar 2" lift and Daystar 3/4" Comfort Ride Spacer.
clayton adjustable rear end track bar ( so I can put a spare 37" underneath )

tire are heavy 37x9.5x12 ta ko2 back rhino.

I used my jeep 35 % towing (rv 5,000). 15 % off road, (5% towing off road gravel Road )
50 % city and high.

current at 65-69 towing the rv getting 18-19 mpg.

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[pokey02]

The diesel will hardly notice a 37" tire with the stock 3.73 gearing. When I ran 37s, I didn't bother with a regear and the jeep drove great. It was a negligible loss of power from stock 33s to 37s.

I recently went to Fusion D60's and 40s and am running 4.56 gears. The jeep drives great and has plenty of get up and go.

I don't tow but do drive to/from the trails.

 

[Minty JL]

4.88s, 4.56s is not a big enough jump to notice.

I'm on 37x13.5s and might go to 39s or 40s .......so I will be going 5.13.

But I'm conflicted.........just finished my MC GC 4.5" kit on my JTM with 37x13.5s on it now and I'm happy with the look. Bigger tire will just mean more rotational mass, need for bigger brakes and more ball joints. So I might just stick with 37s and save the bread for an LS/LT swap.

 

[yrwins]

I forgot to mention I have the diesel version .

 

[JT1]

4.88s, 4.56s is not a big enough jump to notice.

I'm on 37x13.5s and might go to 39s or 40s .......so I will be going 5.13.

But I'm conflicted.........just finished my MC GC 4.5" kit on my JTM with 37x13.5s on it now and I'm happy with the look. Bigger tire will just mean more rotational mass, need for bigger brakes and more ball joints. So I might just stick with 37s and save the bread for an LS/LT swap.

4.88s on a diesel on 37s is overkill and then some.

 

[JT1]

so if "4.88s, 4.56s is not a big enough jump to notice." why they are not using 4:88 ?

You can view the calculator at grimmjeeper. It works extremely well. 4.10s is probably the correct answer if it's doing everything you currently want, but you feel it just needs a little help. It's 150 ish RPMs different at speed in 8th gear between 3.73s and 4.10s.

 

[JT1]

I forgot to mention I have the diesel version .

That isn't diesel advice, I'd roll the 3.73s and save that money for other things.

If you want to see what 4.56s are like at cruise, downshift a gear. 3.73s in 7th is nearly identical to 4.56 in 8th.

 

[Jchap1987]

Don’t forget the front track bar for that Mopar lift

 

[Zachanadandy]

Diesels don't like rpm. Don't waste the money on a regear. 4.10s would be more optimal but that's a bunch of money for a small change. Just run it. If you want more power throw in a tune.

 

[Rusty PW]

From another thread that discussed this. 4.30's is the sweet spot for 37's on the diesel. But no one makes that ratio. So you either go 4.10 or 4.56.

 

[rharr]

From another thread that discussed this. 4.30's is the sweet spot for 37's on the diesel. But no one makes that ratio. So you either go 4.10 or 4.56.

I have a pair of barely used 4:10 take off's sitting in the garage for when i Jump to 37"

You can get take off 4:10's pretty cheap from all the gas ruby guys doing swaps. I got mine from a friend who had very low milage and another friend who did the gear swap, so i knew their history. As a bonus they are OEM Dana gears

 

[Minty JL]

4.88s on a diesel on 37s is overkill and then some.

I'll be honest, I missed the diesel part of the equation

 

[yrwins]

WOW.... that is why I love this forum.
thank so much for good information.
so it Is a BIG NO for 4:88 (I call Yukon and it tell me to used 4:88)

I narrow it down to two 4:11 or 4:56,
I think I will go with 4:56 because I do some towing and I think it will put me closest to factory

Don’t forget the front track bar for that Mopar lift

I was not thinking of a front track bar! do I need one

 

[Minty JL]

WOW.... that is why I love this forum.
thank so much for good information.
so it Is a BIG NO for 4:88 (I call Yukon and it tell me to used 4:88)

I narrow it down to two 4:11 or 4:56,
I think I will go with 4:56 because I do some towing and I think it will put me closest to factory



I was not thinking of a front track bar! do I need one

DO NOT USE YUKON GEARS!!!!!!!!! Unless you want to pay to have gears replaced in under 20k miles or get stranded on the road/trail.

Read the numerous threads about how horrid Yukon Gear and Axle is. Or if you have fuck you money.......take the money it out to your front yard and just set it on fire.......the money that is. Let us know how it all pans out.

 

[howeitsdone]

I think I will go with 4:56 because I do some towing and I think it will put me closest to factory

That's smart. I originally was going 5.13 with my gasser on 37s and ended up having them install 5.38 instead for this reason alone. I'm full time in the camper (4500lbs) and travel all over the country so while there's a small sacrifice while not towing, it's an even greater reward while towing. Especially in that Texas wind I'm sure you're familiar with. Although, your diesel likely doesn't lose as much speed as I do.

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