ecoDiesel JT Rubicon 3.73 Stock w/ 37 inch Mudders: 4.56 or 4.88?

[MOPAR Boy]

So, I have a 2021 Rubicon JT on order, with VIN in hand, but I could only order the 3.73. As soon as it arrives in the next few weeks, I plan to mount my new 37x12.50R17's BFG KM3’s. No doubt the stock 3.73 gearing will be too high, even with the diesel, and it will hunt in/out of 7th/8th gear, particularly at freeway speeds going up hills at 70mph, although I do not tow, ever. I will do about 60% DD with my Gladiator, and 40% off-road, albeit nothing too radical off-road. It's a work vehicle (albeit I own it), and my job takes me to mountaintop sites to service land mobile mtn top 2-way radio repeaters. Some of these washed-out forest service and/or logging roads up to the mtn top are really crazy bad! I'm debating switching to at least 4.10, but that is only a pretty slight (9.9%) change, so I'm looking at changing my gears to either 4.56 or 4.88. If I was running the 3.6 Pentastar, I would lean heavily to the 4.88. My only concern is my freeway cruising needs at 70mph to get to and from the gate, at the bottom of the hill to climb up to the mountain tops. I don’t want to run high rpm’s with my 3.0 eco at 70mph freeway speeds with a 4.88 (power train wear and tear at high rpm’s, let alone bad fuel mileage), so I'm hesitant about 4.88, yet I could see the 4.56 being just not quite enough of what I might want on the storm wrecked-out service roads (more like trails!) to the mtn top.

Anyone here have actual real world experience with your diesel Gladiator running stock 3.73, and changing to 4.56 or 4.88, with some advice?

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[kcZ]

3.73 is just fine with the EcoDiesel on a freeway. Just did a 2000 mile round trip from WI to NC, only downshifting was going up the grades and that was just down to 7th.

 

[Diesel Sting]

I agree, it pulls the 37's just fine IMO.

 

[MOPAR Boy]

3.73 is just fine with the EcoDiesel on a freeway. Just did a 2000 mile round trip from WI to NC, only downshifting was going up the grades and that was just down to 7th.

Are you running 37’s? What rpm at 70mph? Thanks!

 

[Diesel Sting]

As of this morning.

 

[Diesel Sting]

I tried to get one at 80 and ran out of room.

 

[MOPAR Boy]

OK, thanks very much, Diesel Sting! Wow, you went ‘beyond and above!’ Another great example of a “picture is worth a 1,000 words.”

 

[Diesel Sting]

OK, thanks very much, Diesel Sting! Wow, you went ‘beyond and above!’ Another great example of a “picture is worth a 1,000 words.”

No problem!

 

[MOPAR Boy]

No problem!

So, what brand/model tires are you currently running, and are they reasonably smooth at freeway soeeds?

 

[Phil3333]

I have 38's no need for regear unless towing and if I did regear I think 4.30/4.56 is about as low as I would go the diesel is a whole different animal than the 3.6

 

[Diesel Sting]

So, what brand/model tires are you currently running, and are they reasonably smooth at freeway soeeds?

I’m running the M/T Baja Boss’ at 33PSI. We did a beach trip weekend before last and averaged 84mph and 19 MPG. With the windows up and AC on, the tires are not loud at all. I’m only running a 1/2” front 3/4” rear level.

 

[MOPAR Boy]

Oh, thanks so much for the pic, and what a Beautiful Gladiator you have! So, I assume size is 37x12.50R70? Do you get any rubbing, either on or off-road? Does your 373 give you enuf umph when offf-road?

 

[Diesel Sting]

37x12.50x17

I do not get any rubbing lock to lock on road, unfortunately I have not tried it off road yet. I did use 4 low when getting out of my spot at the beach with the lockers engaged and will tell you, it will just creep by itself. With the 4 to 1 ratio in low range, you won't have any issues.

 

[MOPAR Boy]

37x12.50x17

I do not get any rubbing lock to lock on road, unfortunately I have not tried it off road yet. I did use 4 low when getting out of my spot at the beach with the lockers engaged and will tell you, it will just creep by itself. With the 4 to 1 ratio in low range, you won't have any issues.

Wow, sounds great! Your experience is a great reason to choose 3L EcoDiesel over the 3.6 Pentastar, if you want to run big 37’s, and yet still enjoy great fuel mileage, with plenty of power!

What with fuel costs going up and up like crazy with no limits in sight, whilst US fossil fuel production is waning, fuel milegae is becoming a increasingly important consideration in our Jeep purchasing decisions. Electric is great, we have a Tesla and love it, but in this transition phase, I want to hedge my bets. Also, it’s eady to carry some extra fuel cans on a Molly rack, but not so much with electricity. ?‍

 

[Diesel Sting]

I will always have a diesel in the driveway, no matter if it is a 3.0 or a Duramax or Cummins, just never a Ford lol.

IF Ram attaches the 10 speed to the Cummins, this Jeep will be bye bye. I miss that truck but not the trans.

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