3.6L express 3.21 or 3.55 rear ratio?

raven3 · Nov 2, 2015

On a 3.6L V6 Express with 275/60/20 tires, the 3.21 rear ratio is standard and the 3.55 rear ratio is optional.

When test driving both ratios in a Express regular cab short box, seems like the eight speed 845RE transmission shifted more with the 3.55 compared to the 3.21.

Is the 845RE 8 speed transmission more compatable with the 3.21 or is the 3.55 a better choice?

Engine speed at 65 mph in 8th gear is only about 1467 rpm with 3.21 ratio and about 1623 rpm with 3.55 ratio.

darthdzl · Nov 2, 2015

raven3 said:
On a 3.6L V6 Express with 275/60/20 tires, the 3.21 rear ratio is standard and the 3.55 rear ratio is optional.

When test driving both ratios in a XL regular cab short box, seems like the eight speed 845RE transmission shifted more with the 3.55 compared to the 3.21.

Is the 845RE more comparable with the 3.21 or is the 3.55 a better choice?

Engine speed at 65 mph in 8th gear is only about 1467 rpm with 3.21 ratio and about 1623 rpm with 3.55 ratio.

3.55 definitely. I had a tradesman with the 3.21s and a buddy has an express with the 3.55s. The off-the-line response, hill performance, and overall "peppiness" is night and day. The 3.6 will never be a torque monster, but the 3.55s help tremendously, and don't affect fuel economy.

jon0m0berry · Nov 2, 2015

3.55 all day long. itll help with accelerating and moving your truck. it will help your city mpg but itll hurt your highway mpg but itll be negligible. youll do just fine with 3.55

raven3 · Nov 2, 2015

With the 33"diameter tires on the express the engine speed at 65 mph highway speed is about 1467 rpm with 3.21 rear ratio and 1623 rpm with 3.55 rear ratio in 8th gear, about 10% increase in rpm, but higher up on the torque curve to help compensate mpg.

Believe 1467 engine rpm seems too low.
The 5.7l V8 is only available with 3.21 & 3.92 rear ratios, only.

Jerry1984 · Nov 2, 2015

3.55s unless you are driving 85 mph on the highway regularly.

KingTuna · Nov 2, 2015

I test drove both, and went with the 3.55 because I was buying a crew cab. If I was buying a 2wd rcsb, I might go with the 3.21s, but anything else I would go 3.55. With the crew cab, it is more peppy, and definitely helps.

raven3 · Nov 2, 2015

Getting a 2WD RCSB.
3.21 seemed to have less radical shifting than 3.55.
Interesting to note the 3.55 V6 has
slightly greater towing rating than V8
Hemi 6 speed, approximately 150#.
33" diameter tires seems just too large for a 3.21 V6, but all right with
3.21 Hemi V8.

develand · Nov 2, 2015

How do I know what my 14 express has?

Jerry1984 · Nov 2, 2015

Can look up the build sheet or the axle should be stickered. Do you have the window sticker? If so it will be on there as well.

develand · Nov 2, 2015

I looked on the window sticker and didn't see it. I tried doing the VIN look up, but I may not be at the right place to do.

Barcelo5 · Nov 2, 2015

I've been regretting getting the 3.55 ratio as everyone on here has been ranting and raving about the 3.92. But i have the 5.7 v8 with the 6 speed. Maybe every set up has its advantages and disadvantages? I dont find my set up "peppy" at all. Kind of boggy in fact. Wish i had the 8 speed.

raven3 · Nov 2, 2015

It's easy to measure the rear ratio & have performed this procedure many times.
Mark a spot with white paint on the tire or rim & drive shaft tube or rear yoke.

Jack up the rear so one rear wheel is free is free to turn freely and the opposite wheel is grounded.

Rotate the free wheel until the drive shaft completes one full revolution, while counting the number of wheel revolutions.

Divide the wheel revolutions by two.

The result is the rear end differential gear ratio.
The number of wheel revolutions is not an interger, like 6 or 7.
It will be something like 6-1/2 turns/2= 3.25, which is a 3.21 rear ratio.
If it is something like 7-1/8 turns/2 = 3.61, which is a 3.55 rear ratio.

If the rear end differential is a locking type, jack up both rear wheels, so each rear wheel turns freely.
Turn one rear wheel until the drive shaft completes two revolutions, then divide the number of wheel revolutions by two. The result is the differential gear ratio. Two revolutions are required to obtain adequate accuracy.

raven3 · Nov 2, 2015

Believe the 5.7 V8 is matted to 3.21 & 3.92, only,with both 6 & 8 speed.
3.6 V6 is matted to 3.21 & 3.55 , only, with 845RE 8 speed.

1st gear for 6 speed is 3.00:1
1st gear for both 8 speeds are 4.70:1, much faster out of the hole than 6 speed.

Hemipower392 · Nov 3, 2015

Your ratio on your rear diff. and my 3.6 with the 3.55 handles my tires well

Barcelo5 · Nov 4, 2015

raven3;1154#'s 17 said:
Believe the 5.7 V8 is matted to 3.21 & 3.92, only,with both 6 & 8 speed.
3.6 V6 is matted to 3.21 & 3.55 , only, with 845FE 8 speed.

When i put my vin # in the ram website, it shows 3.55 in the equipment listing. Thought i saw that on the actual diff but its hard to read.

RamGator · Nov 11, 2015

What is the website to check the ratio?

How much would it cost to change it to the 3.55?

darthdzl · Nov 11, 2015

RamGator said:
What is the website to check the ratio?

How much would it cost to change it to the 3.55?

Put this in your browser, and add your VIN (all uppercase for the letters) at the end, no spaces.

http://www.chrysler.com/hostd/windowsticker/getWindowStickerPdf.do?vin=

(Copy the link, not the text...if you get the "..." in the middle of it, it won't work.)

As for cost to change to 3.55s, it depends. If you have a 4WD, it'll be expensive. You can't just change the gears in the front after 2011 or so; they're welded in, so you have to replace the whole front end as well as the rear gears. There are other threads that talk about this.

If you have a 2WD, it's not too bad. Contact someone like Moe's Performance. Parts would likely be $500ish, and then there's labor. 3.92s also become an option as well. It's just the factory that doesn't offer them on V6s; there's nothing preventing them from working if installed aftermarket.

Just make sure you get the ones for ZF axle specifically. They switched to those after 2011, I think, and although it's the same size (9.25"), the ones from the older rear ends won't work (without changing a bunch of different hardware; Moe or others can give you details on that).

jag1886 · Nov 11, 2015

Barcelo5 said:
I've been regretting getting the 3.55 ratio as everyone on here has been ranting and raving about the 3.92. But i have the 5.7 v8 with the 6 speed. Maybe every set up has its advantages and disadvantages? I dont find my set up "peppy" at all. Kind of boggy in fact. Wish i had the 8 speed.

Maybe you should crawl under the back and check. A lot of 6 speed trucks that the window sticker said 3.55 had a 3.21, I know mine did and the dealer wouldn't do crap about it because the OE factory (computer generated) build sheet said it was built with a 3.21. Window sticker means nothing.

TerraNewf · Nov 16, 2015

I have the 3.21 ratio and have no complaints. Having said that I have never driven a Pentastar with 3.55's so I can't compare. Very satisfied with my setup, even tow a 6x10 enclosed trailer with my quad in it on occasions. This quick of the line stuff doesn't interest me, if I want to go there I'd be driving a Hellcat Challenger/Charger.

raven3 · Nov 20, 2015

Is the programming software for the V6 845RE Trans for the 3.21 rear ratio different than the programming for the 3.55 rear ratio?

3.6L express 3.21 or 3.55 rear ratio?

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