3.55 Rear Axel Ratio

[mcat79]

I'm building out my config and looking to place an order with MD tomorrow. I've read so much about 3.21 vs 3.92, but no one ever seems to mention 3.55. Is this something I should consider? Mostly flat driving, light trailer hauling. Just curious if this is a good compromise or if I should just stick with the 3.21 for mpg. This will be paired with the 5.7

 

[jws1982]

If you’re hauling a light trailer most of the time then the 3.55 would keep it in eighth gear more often, giving you a smoother highway ride. You don’t need 3.92 at all for your purposes unless you just want quicker acceleration in 1st gear.

3.21 or 3.55 would be fine. If I usually had a light trailer hooked up, I’d go 3.55.


Sent from my iPhone using Tapatalk

 

[mcat79]

I figured the 3.92 would be overkill. Would the 3.55 give a noticeable benefit in acceleration? Any thoughts on MPG difference between 3.21 and 3.55. While I will have a light trailer, most driving will be without a trailer.

 

[Idahoktm]

You can't get 3.55 with the 5.7.

 

[mcat79]

You can't get 3.55 with the 5.7.

You're right, I saw it as an option and assumed I could. I just tried on the build and sure enough it switched to the v6. Well that makes that decision easy and explains why no one else was discussing the 3.55. I feel like an idiot.

 

[Idahoktm]

You're right, I saw it as an option and assumed I could. I just tried on the build and sure enough it switched to the v6. Well that makes that decision easy and explains why no one else was discussing the 3.55. I feel like an idiot.

I tried it too. Not sure why 3.55 isn't available with the 5.7. It would be a popular choice.

 

[jws1982]

I tried it too. Not sure why 3.55 isn't available with the 5.7. It would be a popular choice.

Definitely would.

In OP’s case, for sure go 3.21 over the 3.92. At 70, 3.21’s have the engine around 1600 rpm. 3.92’s will have it close to 2000 rpm. Definite difference in fuel economy in flatter areas.


Sent from my iPhone using Tapatalk

 

[397STROKER]

If you plan on lifting/leveling and putting bigger tires on I would go with the 3.92s.

 

[bigdodge]

Definitely would.

In OP’s case, for sure go 3.21 over the 3.92. At 70, 3.21’s have the engine around 1600 rpm. 3.92’s will have it close to 2000 rpm. Definite difference in fuel economy in flatter areas.


Sent from my iPhone using Tapatalk

i would like to see the torque curve
before I would say your statement is true.

 

[Idahoktm]

Definitely would.

In OP’s case, for sure go 3.21 over the 3.92. At 70, 3.21’s have the engine around 1600 rpm. 3.92’s will have it close to 2000 rpm. Definite difference in fuel economy in flatter areas.


Sent from my iPhone using Tapatalk

I don't want to turn this into another 3.92 vs 3.21 argument, but you would need to spend the majority of your time on the highway for 400 RPM's to make a significant difference in fuel economy. If the OP doesn't do a lot of highway cruising, he might want to consider 3.92's.

Edit: I drove on the freeway yesterday....3.92 gearing: 70 mph=1700 rpm. 75 mph=1900 rpm.

 

[teamroper60]

I'm building out my config and looking to place an order with MD tomorrow. I've read so much about 3.21 vs 3.92, but no one ever seems to mention 3.55. Is this something I should consider? Mostly flat driving, light trailer hauling. Just curious if this is a good compromise or if I should just stick with the 3.21 for mpg. This will be paired with the 5.7

I dont know what your definition of light trailer hauling is, but for reference, I live in Missouri, where flat towing virtually doesnt exist. I tow a fiberglass bass boat with my truck (5.7 etorque, 3.21 gears) without any problem and average 15mpg doing it. Empty, I am averaging 19-20mpg, depending on speed.

 

[Dragonmaster13]

I think Ram is missing a better CAFE rating by not offering 3.55 or 3.73s for both engine variants. The ED runs at 2000rpm at 75, and drops from 27mpg in my rebel at 70 to 25-26 at 75. A few hundred less revs would be great. Too bad regearing the front axle is a major PITA, as in you need to buy a new carrier and housing, otherwise $3500 would be dropped in a heartbeat to go from 3.92s to 3.73s in my 4x4

 

[Idahoktm]

I think Ram is missing a better CAFE rating by not offering 3.55 or 3.73s for both engine variants. The ED runs at 2000rpm at 75, and drops from 27mpg in my rebel at 70 to 25-26 at 75. A few hundred less revs would be great. Too bad regearing the front axle is a major PITA, as in you need to buy a new carrier and housing, otherwise $3500 would be dropped in a heartbeat to go from 3.92s to 3.73s in my 4x4

You would blow $3500 for a 2 mpg gain at 75 mph? It would take you 150,000+ miles to break even and that's if you drove 75 mph 100% of the time.