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

[VA6489]

Talked to EoC when I bought my tuner and delete kit. they recommended 4.56 gears 37-40 inch tire. Sweet spot for max torque is 2100 rpm. cruise is 1750 rpm, best eco 1500 rpm. Local shop installed 5.13 in a JTRD here and had issues on the highway. Chatted with East Coast Gear and supply they also recommended 4.56 for a 38 inch tire.

Inststalling a semi float D60 from ECGS with 4.56 gears. Runnign BFG 39s, measure out at 38 inch.

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[JO_178]

I have 37's with 5.13's. I'm glad I went with the 5.13

 

[JT1]

I have 37's with 5.13's. I'm glad I went with the 5.13

The diesel is a completely different animal than the 3.6 trucks. 5.13s are way too deep even for 40's.

 

[JO_178]

True story. Mine is a 2024 with the 3.6. With the Diesel 4.56 would be right

 

[Josh00333]

37" 4.88 100%. Even with 35" some guys prefer 4.88's. I run a funky 4.63 w 35"'s and its very

 

[RKcreative]

LOL, gotta love the gas guys chiming in on a re-gear thread in the 3.0 diesel section—"Oh, I didn't know it was a diesel."

Just hit 63K miles on my ’22 JTRD. Lifted it at 3K miles, originally on 38s, now running 37s. Still on stock gearing, but I do have a Pedal Monster. I live in Denver, so all my driving is at elevation with plenty of elevation changes.

Originally, I ran a bed rack with an RTT, but I’ve since switched to an Alu-Cab canopy and tow an overland camper. The only time I de-rated was while towing (~3,500 lbs) over Vail Pass in the summer. That was partially my fault—I was pushing it too hard speed-wise. Naturally, diesels run hot over mountain passes when towing, but if I take it easy and lower my speed, she cools right off and does just fine.

As for re-gearing, 4.10s are the closest to factory ratios for a diesel on 37s. I don’t plan on going any taller tire-wise, and honestly, as many have pointed out, going from 3.73s to 4.11s is such a small change that I question whether the cost is worth it. That said, AEV runs 4.56s on their diesel package builds.

My advice? Drive your rig and see how it performs. The Pedal Monster made a huge difference in drivability—it completely eliminated the low-RPM lag that's programmed into the throttle map. Highly recommend it.

Ultimately, with the weight of your camper and how often you tow, 4.56s might be the best option for you. There are also multiple threads with small hacks to help the diesel run cooler. Some popular suggestions include removing the engine cover and opening up the hood vents to improve airflow.

 

[caryt]

Best mod to help cooling is a Tazar..I turn the fan on high before I get to a big hill and so far never had it derate or get over 235* oil temp on any grade here in the summer. Water temps never a issue or trans.

 

[mgenbox]

Best mod to help cooling is a Tazar..I turn the fan on high before I get to a big hill and so far never had it derate or get over 235* oil temp on any grade here in the summer. Water temps never a issue or trans.

Wow that is good to know. I will try this
That level is prob non towing?

 

[rharr]

Just to chew on, bigger ratio, smaller pinion, smaller pinion, less strength. Combine less strength with bigger tires/leverage you increase chances of breaking a pinion.

Just putting this here as a consideration for not going to crazy on gearing depending on what you plan to do.

 

[CrazyCooter]

Best mod to help cooling is a Tazar..I turn the fan on high before I get to a big hill and so far never had it derate or get over 235* oil temp on any grade here in the summer. Water temps never a issue or trans.

While I can confirm this method does offer a minimal improvement in getting ahead of things, you still end up derating on the hill eventually.

Even with the aux radiator, I still see derating, it just takes longer to get there and recovery is lightening fast after cresting/coasting.

 

[mgenbox]

While I can confirm this method does offer a minimal improvement in getting ahead of things, you still end up derating on the hill eventually.

Even with the aux radiator, I still see derating, it just takes longer to get there and recovery is lightening fast after cresting/coasting.

Curses

 

[caryt]

I have never derated or gone over 240* oil temps even when late to turn the fan on high and we have 6*+ grades everywhere. I di not tow at 7400lbs I'm way over weight on the rear axle as it is plus absolutely hate towing.

 

[CrazyCooter]

I have never derated or gone over 240* oil temps even when late to turn the fan on high and we have 6*+ grades everywhere. I di not tow at 7400lbs I'm way over weight on the rear axle as it is plus absolutely hate towing.

I have quite possibly the highest number of heavily loaded towing miles of anyone on here since I only use this truck for roadtrips generally with the RV or hauling trailers to/from landscaping supply or the dump. Many of our trips towing have been 2500-6000 miles.

We have 9% grades when traveling east or west and 6% north just to leave town. I pretty regularly exceed 9% grades on almost any given trip. Ambient temps here in the summer regularly hit 110° and sometimes 119°!

While we generally only tow a 4,500'ish RV or 5500'ish dump trailer, the GCVW is constantly running up to the max 12,000'ish GCVWR if I remember correctly?

I can tell you the truck derates on every trip unless I'm traveling south into the valley below 90° ambient or temps are near/below freezing in the mountains. This with the aux radiator installed and gears swapped for the oversized tires as well.

There just isn't enough cooling system to run a 100% duty cycle. Otherwise I'm pretty happy with the truck overall.

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