Decision time 4:56 or 4:88

[CincyCuda68]

‘18 2500 6.4 with 3:73
37” tires and 6” lift.
Towing 36’ toy hauler.

Which way do I go and what is the effect on highway speeds? I rarely go over 75 and don’t want to completely kill the whopping 13 mpg for regular (non towing) driving.

7792C4AB-37FF-4265-8230-D478320B1217

• CincyCuda68
• May 18, 2021

 

[G-Ride990]

Holy cow man where you been? Truck and trailer are looking great!

 

[CincyCuda68]

Holy cow man where you been? Truck and trailer are looking great!

I had to get off here it costs way too much $$$ and thank you!!

 

[El Huapo]

does this help?

Engine RPM Calculator | Spicer Parts

gotta know trans ratios too.

 

[CincyCuda68]

does this help?

Engine RPM Calculator | Spicer Parts

gotta know trans ratios too.

Another member sent me the chart. 6th is .63, looks like I’m going 4:88

3.73 gear at 75mph on 33" 1760 rpm
4.10 gear at 75mph on 37" 1750 rpm
4.56 gear at 75mph on 37" 1950 rpm
4.88 gear at 75mph on 37" 2100 rpm

 

[Bldrinker]

You want 4:88

ask me how I know. I have 34” tires and have a 12000-14000lb trailer depending on what we are doing.

You might want to consider 5:13 if you don’t daily it

 

[CincyCuda68]

You want 4:88

ask me how I know. I have 34” tires and have a 12000-14000lb trailer depending on what we are doing.

You might want to consider 5:13 if you don’t daily it
View attachment 247824

Damn how long is that thing? Mine is 36.5’ and 11,200 with the side by side in there.

 

[CincyCuda68]

You want 4:88

ask me how I know. I have 34” tires and have a 12000-14000lb trailer depending on what we are doing.

You might want to consider 5:13 if you don’t daily it
View attachment 247824

I’m in Ohio and pulled it to Utah last fall. It was an easy trip and the truck did fine with the 3:73 with one huge exception, the Rocky Mts. That was a nightmare. 2 hours of 5,000 rpm going 20 mph. Hoping 4:88 will make that significantly better.

 

[Bldrinker]

Damn how long is that thing? Mine is 36.5’ and 11,200 with the side by side in there.

37’ tip to tip. Has huge kitchen/living slide plus master bed slide. Dual ac 150 gal fresh 40 gal fuel blah blah blah. It’s 10,000 dry with nothing in it.

 

[CincyCuda68]

37’ tip to tip. Has huge kitchen/living slide plus master bed slide. Dual ac 150 gal fresh 40 gal fuel blah blah blah. It’s 10,000 dry with nothing in it.

Looks so much longer than mine but it isn’t. I guess hard to tell in pics. Mine is a bit lighter at 8900 empty 132 gal fresh 30 gal black 30 gal grey and single slide. 21 gal fuel.
Looks sweet, I was kind of worried about pulling that much weight with a 6” lift and 37’s but it wasn’t really an issue.

 

[Bldrinker]

I’m in Ohio and pulled it to Utah last fall. It was an easy trip and the truck did fine with the 3:73 with one huge exception, the Rocky Mts. That was a nightmare. 2 hours of 5,000 rpm going 20 mph. Hoping 4:88 will make that significantly better.

View attachment 247836

It’s not going to help you keep the RPM down much at all. You may be able to do a gear higher up the hills and 5-10mph faster. But the 6.4 has to scream to do anything.

The gears will help you get rolling that 1-2 shift sucks. The gears help that.

You will be able to hold a gear higher on the freeway. With a bit better rpm.

You have bigger tires and starting with worse gears. So you may experience a bigger difference.

I went from 4:10 and stock tires to
4:88 and 34’s.

 

[CincyCuda68]

It’s not going to help you keep the RPM down much at all. You may be able to do a gear higher up the hills and 5-10mph faster. But the 6.4 has to scream to do anything.

The gears will help you get rolling that 1-2 shift sucks. The gears help that.

You will be able to hold a gear higher on the freeway. With a bit better rpm.

You have bigger tires and starting with worse gears. So you may experience a bigger difference.

I went from 4:10 and stock tires to
4:88 and 34’s.

I will be happy if I can get 30-35 mph, then I can tuck in behind a semi on the mountains and it will be fine. I quite literally couldn’t get more that 20-25 on the uphills. It’s a bit scary with cars blasting by at 75-80 lol.

 

[Blanked]

You drive 75 when towing??

 

[CincyCuda68]

You drive 75 when towing??

Uh no, when not towing, not like I can swap gears just when I’m towing. Need to run 75 for daily driving on the highway.

 

[GsRAM]

From the research I've done, with your lift and 37s, strongly consider 5.13s. Check that rpm calculator to see where you'd be at.

A few folks running stock tires have gone from 3.73s to 4.56s and wish they would have gone to 4.88s, on stock tires. Some with lifted trucks have gone to 4.88s and wish they'd have done the 5.13s.

Something to think about because at your loaded trailer weight. With that monster trailer your towing, your already in Cummins territory so as it is, in my opinion, even on stock tires. I dont think the 5.13s would be too much gear with 37s, personally at the weights your pulling. It's a big decision I know.

I'll just add that typically folks that regear dont post that they wish they would have gone with less gear, they report they wish they'd gone with a taller gear.

Good luck with your decision.

 

[Toddz]

I would say to visit
http://www.grimmjeeper.com/gears.html
If you do a lot of freeway driving at 75 when not towing, you can figure out what your rpms will be using the above calculator. Then go out and use your gear selector to drive around at that rpm to see if that is where you want to be.

 

[RamminMopar]

With how big your truck and trailer is id go 5.13 for sure, that extra get up and go is nice on these rfe hemis

 

[RoadRamblerNJ]

5.13's. You won't regret it one bit. As stated previously, nobody comes back and complains about going to 4.88s or 5.13s. Keep the revs up, That 6.4 does not like to lug. You will think you're in a different truck at first. In the good way.

Sent from my SM-N910V using Tapatalk

 

[BlueMule]

6.4L with the 6speed trans here. I don't tow anything and I went from 4.10's and 33's to 4.88's and 37's. Plenty of get up and go for acceleration. I cruise 75 with plenty of power on the highways. She will downshift on hills at highways speeds. But if I were to tow anything significant, I would go to 5.13's. Or just trade it and get a Cummins like someone above said. I can't quite remember, but the parts and labor for the gear upgrade was $2000-2200/2300 for me in Maryland.

 

[Bldrinker]

Well I’m heading out tomorrow. Truck and trailer are loaded heavier than it ever has. 150 gallons of water, 40 gallons of fuel 2 15 gallon propane’s, 2 quads. Enough food, clothes and alcohol for 6 days. If anyone has done the hill north of Bishop, CA on the 395. You know how bad I’m gonna be hurting.

If I can avoid 1st gear I will be impressed.

This is Truck and trailer empty.