4.56 or 4.88 w/ 6.4

[FlatbedHemi]

I regeared my truck to 4:56's about a year ago. I cruise the highway at 2,000 RPM's at 70 mph. I typically see 16/17 mpg on the highway and 13/14 in town (summer gas and calculated via the dash). In the winter I lose about 1mpg. Towing my trailer, I see 7/8 mpg depending on load and headwinds. I don't exceed 65mph with the RV trailer. I do drive like a gentleman. One thing to note as well, my MDS does not come on anymore then it did before. MDS is pretty much un-useful and only activates when my truck is slowing down.The biggest thing to consider is when using tow/haul mode with a geared truck, the computer locks out 6th gear. In tow/haul mode at 65mph (5th gear), I'm turning 2500 RPM's which is just right for my RV towing needs. I really don't want to go any faster with my RV trailer. But when I'm towing the flatbed with a car on it, I can't use tow/haul because I like to go faster and it will push the rev's further than I like. Something else to think about.

Now that I have over 15,000 miles on my 4:56's, I have no regrets and would not go any lower. Below is a quote from my initial post regarding my gear swap.




View attachment 171738

Are you still running stock size tires to get those numbers?

 

[SuperBeeMike]

Yep, Stock Firestone AT's. 275/70R18's (33")

 

[olyelr]

Yep, Stock Firestone AT's. 275/70R18's (33")

Exactly, but toss some heavier 35’s or 37’s under there and what would you do. For stock size tires though, yea I can see sticking with 4.56’s.



Very informative prior post, thanks

 

[FlatbedHemi]

Yep, Stock Firestone AT's. 275/70R18's (33")

That’s more of what I was wanting to hear. I guess I have decided to buy into the 4.88 idea. Now I need to figure out what brands are the most reliable and quiet. I hear that the nitros can be loud, and AAM make the factory sets, but what about Yukons? The local shop I talked to said Yukons were the only brand they could get in 4.88. Said the AAMs only go to 4.56.

 

[olyelr]

That’s more of what I was wanting to hear. I guess I have decided to buy into the 4.88 idea. Now I need to figure out what brands are the most reliable and quiet. I hear that the nitros can be loud, and AAM make the factory sets, but what about Yukons? The local shop I talked to said Yukons were the only brand they could get in 4.88. Said the AAMs only go to 4.56.

Last I checked, you could get up to 5.13’s from AAM.

 

[SuperBeeMike]

Two thoughts I had when deciding on a gear change. First was utilizing factory AAM gears. I'm not a fan of buying foreign made components if I don't have to. I did not want to compromise on something like this if I was spending that kind of money. I found a local shop that uses factory parts and gave me a warranty to back it up. I do not have experience with Yukon or Nitro but if I recall, they were foreign made. I've bought enough made in China crap over the years to steer clear when possible.

Lastly, I read an article about pinion size and heat generated by going to a smaller pinion gear. I wish I could find it again so I could share. From what I remember, when going lower with the gear set, the pinion gear is significantly reduced in size, and contact area, to account for the change in the ring gear. The smaller contact area has less surface to transfer the energy, therefore putting more pressure on the surface and oil, causing more heat. It also puts more stress on the gear itself. Since my truck is mainly used for towing, it had me worried about going to low and having a tiny pinion gear. That article might have been B.S. but it did have me thinking. Anyway...Food for thought.

Regardless of which direction you go, it is money well spent. Hope all of this helps - Mike

That’s more of what I was wanting to hear. I guess I have decided to buy into the 4.88 idea. Now I need to figure out what brands are the most reliable and quiet. I hear that the nitros can be loud, and AAM make the factory sets, but what about Yukons? The local shop I talked to said Yukons were the only brand they could get in 4.88. Said the AAMs only go to 4.56.

 

[WY.Ram]

5.13 AAM, MDS delete, 305/70r18 (35x12.5 ish) Mickey Thompson MTZ:

11.5 mpg city / 13.0mpg highway (85mph)

----------------------------------------------------------
4.10 AAM, MDS activated (doesn't do ****), 305/70r18 (35x12.5 ish) Mickey Thompson MTZ:

10.5 mpg city / 13.5mpg highway (85mph)

7000 to 12000ft above the sea, and I step on the pedal like I'm towing 16k lbs, but I'm not.
My wife calls me a lot of things when we get out of the wagon, 'gentleman' isn't even close. Lol

Those are all EVIC numbers


2016 RAM 2500 pw | 392ci w 6spd | CAI w ARH long tubes & Solo | Diablo T2 w HF tune | 5.13 AAM w 35" Mickey MTs | Custom Graphics w illegal tint | Dodge Off-Road

 

[RoadRamblerNJ]

5.13 AAM, MDS delete, 305/70r18 (35x12.5 ish) Mickey Thompson MTZ:

11.5 mpg city / 13.0mpg highway (85mph)

----------------------------------------------------------
4.10 AAM, MDS activated (doesn't do ****), 305/70r18 (35x12.5 ish) Mickey Thompson MTZ:

10.5 mpg city / 13.5mpg highway (85mph)

7000 to 12000ft above the sea, and I step on the pedal like I'm towing 16k lbs, but I'm not.
My wife calls me a lot of things when we get out of the wagon, 'gentleman' isn't even close. Lol

Those are all EVIC numbers


2016 RAM 2500 pw | 392ci w 6spd | CAI w ARH long tubes & Solo | Diablo T2 w HF tune | 5.13 AAM w 35" Mickey MTs | Custom Graphics w illegal tint | Dodge Off-Road

I've been lookin' for you bro. Mom says we're twins! Ha ha ha

 

[RoadRamblerNJ]

OP, keep one thing in mind about gear ratios. The ratio is only what it's called (4.56:1 or 4.88:1) when you're in your trucks 1:1 gear. My '17 2500 6.4 is 1:1 in 4th. In 6th gear, my tru ratio is 2.85:1. That's "highway gearing" brother.

I was running 4.88s on the street back in the 70's with a Muncie M-22 close ratio 4-spd. You run out of engine RPMs real fast with no over drive gears like we have now. Multiply your top gears ratio by your rears ratio to get true ratio. eg. My 6th gear is 0.625:1. So, my final drive ratio's are...
0.625 X 4.56 = 2.85
0.625 X 4.88 = 3.05
0.625 X 5.13 = 3.21

 

[FlatbedHemi]

Yeah, I have been playing with the calculator pretty frequently comparing my setup to other trucks I have owned, considering their performance and comparing that to other makes and models I am familiar with. That’s what ultimately convinced me to run 4.88, but I needed confirmation that by going with a slightly taller gear wasn’t gonna net me any better fuel mileage (yeah, 1mpg is significant to me, but I am crazy). What really didn’t help was that everyone on here drives like a nut on a circle track, , so finding someone who drives conservatively and gets decent mileage at the RPM I was looking at was just extra reinforcement that I would be happy with the 4.88 ratio.

 

[allenmp]

2017 2500 crew cab long bed 4x4
Leveled with 35/12.5 18 mt/at hybrid tires
373 to 4.88 nitro gear swap 5000 miles ago
Anything over 55 my mds is pretty much non existent
90% highway driven since i got the truck
I averaged 13-16 pending on blend
Now with 4.88 it stays closer 14-15 running anywhere from 65-75 at 55 around 16 or so
So i think fuel mileage is a wash
What i have pulled with the new gears vs old and the daily driveability of the truck is where the improvement comes in
Any driving condition you can possibly think of is improved by leaps and bounds
Mds kicks in when driving around town a lot
It holds gears so much better
I pulled a 9000 pound trailer not too far but got 12 to 12.5
It's just so much more of a pleasure to drive now
And if your mood says you want to stomp on it on occasion
It will not disappoint it just moves
If your truck has a heavy flat bed and tools i would opt for the 88's no question about it
I was afraid it would be too low when i asked a bunch of questions i went with them
I am very happy with them

 

[Mountaineer83]

2017 2500 crew cab long bed 4x4
Leveled with 35/12.5 18 mt/at hybrid tires
373 to 4.88 nitro gear swap 5000 miles ago
Anything over 55 my mds is pretty much non existent
90% highway driven since i got the truck
I averaged 13-16 pending on blend
Now with 4.88 it stays closer 14-15 running anywhere from 65-75 at 55 around 16 or so
So i think fuel mileage is a wash
What i have pulled with the new gears vs old and the daily driveability of the truck is where the improvement comes in
Any driving condition you can possibly think of is improved by leaps and bounds
Mds kicks in when driving around town a lot
It holds gears so much better
I pulled a 9000 pound trailer not too far but got 12 to 12.5
It's just so much more of a pleasure to drive now
And if your mood says you want to stomp on it on occasion
It will not disappoint it just moves
If your truck has a heavy flat bed and tools i would opt for the 88's no question about it
I was afraid it would be too low when i asked a bunch of questions i went with them
I am very happy with them

Are you hearing any noise at all with the Nitros now? I really want 4.88s for towing heavy, but I know you had issues at first with the shop having some noise after initial install.

 

[FlatbedHemi]

Are you hearing any noise at all with the Nitros now? I really want 4.88s for towing heavy, but I know you had issues at first with the shop having some noise after initial install.

I have the same question for anyone with Yukon. The shop I talked to uses Yukons primarily but I read somewhere that someone had a noise problem with the Yukons.

 

[allenmp]

Are you hearing any noise at all with the Nitros now? I really want 4.88s for towing heavy, but I know you had issues at first with the shop having some noise after initial install.

There is still a little noise they quieted down a lot after the 500 mile break in
Thet also said the crush sleeve was the wrong one the first time round
Now it's hardly noticeable either I'm used to it or it's quieter lol
There is still a little low gear whine on deceleration but not too bad
Over all i am very happy with them
I figured at 10k i will do another inspection and oil change but do far the only regret i have is not doing it sooner

 

[Mountaineer83]

Awesome! I look forward to getting mine done eventually. I ended up using some of my gear money for tires on my wife's car and a more secure tonneau cover.

 

[RoadRamblerNJ]

There is still a little noise they quieted down a lot after the 500 mile break in
Thet also said the crush sleeve was the wrong one the first time round
Now it's hardly noticeable either I'm used to it or it's quieter lol
There is still a little low gear whine on deceleration but not too bad
Over all i am very happy with them
I figured at 10k i will do another inspection and oil change but do far the only regret i have is not doing it sooner

Yes Sir. I can't wait. Those 4.88s I had in my '72 Camaro were FUN! I know nobody but my NJ brethren will get this but we had a saying back then. "First one outta the toll booth but the Last one down the shore!

 

[[email protected]]

I'm running 4.56 with 37's. AAM in the front and Nitro in the rear. Love them and have zero complaints RPM'S are great and drivability much improved from the 3.73's. But slight noise on deceleration.

 

[RamminMopar]

Anyone re gear a 5.7?

 

[RoadRamblerNJ]

I'm running 4.56 with 37's. AAM in the front and Nitro in the rear. Love them and have zero complaints RPM'S are great and drivability much improved from the 3.73's. But slight noise on deceleration.

Easy fix...louder mufflers.

Ever been in a car with a blower on it? It whines like all get out. That is a sweet sound you never get tired of hearing. Makes grown men giggle.

 

[RoadRamblerNJ]

I'm running 4.56 with 37's. AAM in the front and Nitro in the rear. Love them and have zero complaints RPM'S are great and drivability much improved from the 3.73's. But slight noise on deceleration.

Since your 4.56 upgrade with the 37's, have you ever wished you done 4.88's or 5.13's?