An Engineer's Ultimate Guide To 3.21 VS 3.92 Axle Ratio

[jimchi]

So glad I went 3.92 after looking at the scale, thanks.

Actually in my line of work, most of them lack common sense, but anyway.

Glad to help. I’m an engineer too, by the way. I’ve noticed that those who share such opinions don’t realize that engineering decisions rarely are black and white. There are multiple factors that go into any engineering decision, e.g. economical, ethical, ease of service, scope, etc., and the end result is a compromise to best meet a design goal. Just food for thought.

 

[bwsRam19]

Glad to help. I’m an engineer too, by the way. I’ve noticed that those who share such opinions don’t realize that engineering decisions rarely are black and white. There are multiple factors that go into any engineering decision, e.g. economical, ethical, ease of service, scope, etc., and the end result is a compromise to best meet a design goal. Just food for thought

I hear you, the place where I work likes to hire them fresh out of college with no real world experience. I'm sure your good at what you do.

 

[dannymcd]

I really enjoyed reading this post, I completely understand how the axle ratio works, but it was great to get that info in such a specific to the Ram trucks way. After reading this I just thought how complicated this would be on the F150 with their 4 different ratio's, which is also one of the many reasons I avoided buying the F150.

 

[bwsRam19]

I really enjoyed reading this post, I completely understand how the axle ratio works, but it was great to get that info in such a specific to the Ram trucks way. After reading this I just thought how complicated this would be on the F150 with their 4 different ratio's, which is also one of the many reasons I avoided buying the F150.

lol, giving you more options was a reason to avoid them?

 

[Mountain Whiskey]

I hear you, the place where I work likes to hire them fresh out of college with no real world experience. I'm sure your good at what you do.

I deal with the same thing....

 

[GadgetMason]

Thanks! That's true, people seek evidences that support their own beliefs. For 3.92 lovers here, I list the exact reason why 3.92 is better for towing, and for 3.21 lovers, I list exact reason why 3.21 is better for fuel economy. There's something for everyone. Personally, I am leaning 3.21 because I don't plan on owning a boat over 5000lbs, and all the 8000lb and above travel trailers require a 5th wheel found in HD trucks. To be honest, I would most likely be hauling air 99% of the time. If I ever own a boat over 10000lbs, I would probably have enough money laying around for a F350 Tremor. I'm sure many of you with horses or heavy construction equipment would benefit greatly from 3.92. I'm just an engineer chained to a desk.

Since one day I'm looking to get a toy hauler for my bike, I'm glad I chose the 3.92!

 

[Willwork4truck]

So glad I went 3.92 after looking at the scale, thanks.

I still want a 3.55 gear hemi option in the 5th gen.

 

[Willwork4truck]

I really enjoyed reading this post, I completely understand how the axle ratio works, but it was great to get that info in such a specific to the Ram trucks way. After reading this I just thought how complicated this would be on the F150 with their 4 different ratio's, which is also one of the many reasons I avoided buying the F150.

Ford restricts their gearing choices by engine. You cannot get every engine with just any gearing. From the thread listed BELOW, post #16:
"If you opt for Max Tow, 3.55 e-locker is the only gear option you'll have.

If you opt for the Heavy Duty Payload package, 3.73 is the only available choice. That package itself is generally only available on #00A option levels.

If you don't pick either one of those, you'll have your choice of a 3.31 standard or e-locker, 3.55 e-locker.

Note: my example is via the build & price page for the 2018 F-150 Lariat trim level."

Here's their "engineers guide" chart: https://www.f150forum.com/f118/what-rear-end-gear-ratio-2018-3-5-ecoboost-10-speed-4x4-397864/
"Agree with chimmike... below table shows total gear reduction comparison between 6 spd and 10 spd."

And finally, a different Ford thread post #4 sums it up well: https://www.f150ecoboost.net/threads/question-about-10sp-2-7-and-gear-ratio.65377/
"With a 10 speed transmission, this is almost a "doesn't matter" scenario.
Final drive ratio has SO much overlap now between 1st and 10th gear, regardless of rear-end gear.
Our granddaddies had a very important decision to make, and one they had to live with if they got it wrong.
They'd laugh at us today for worrying too much about getting it right.
Or put another way, it's hard to get it so wrong that we are tortured by it. That modern transmission just has so much covered."

 

[Willwork4truck]

It's fun to read other threads/posts on competitors forums. Here's a Ford one from 2017 where the guy wants a 4" lift and 35's and is concerned about getting good mpg's...: https://www.ford-trucks.com/forums/1513296-what-gear-ratio-is-best-for-me-mpg-2.html
"darn it now you got me considering the 2.7. I had my heart set on the 3.5, but now I'm researching the 2.7 and I'm thinking that might be better. My only concern would be I may at times have to tow 2 classic vehicles at once which would put me at around eleven thousand pounds, and that's only a maybe that I might have to tow that. So now would the 2.7 on say 33s and a mild lift do better with MPG than the 3.5?

So don't think that all the questions on gears is just a "RAM thing".
You've got F150 owners trying to tow 11K while lifted and wanting good mpg's... Right.

 

[jimchi]

It's fun to read other threads/posts on competitors forums. Here's a Ford one from 2017 where the guy wants a 4" lift and 35's and is concerned about getting good mpg's...: https://www.ford-trucks.com/forums/1513296-what-gear-ratio-is-best-for-me-mpg-2.html
"darn it now you got me considering the 2.7. I had my heart set on the 3.5, but now I'm researching the 2.7 and I'm thinking that might be better. My only concern would be I may at times have to tow 2 classic vehicles at once which would put me at around eleven thousand pounds, and that's only a maybe that I might have to tow that. So now would the 2.7 on say 33s and a mild lift do better with MPG than the 3.5?

So don't think that all the questions on gears is just a "RAM thing".
You've got F150 owners trying to tow 11K while lifted and wanting good mpg's... Right.

2.7 and 3.5 are referring to the engine sizes, specifically the V6 EcoBoost offerings in the F150

 

[Willwork4truck]

2.7 and 3.5 are referring to the engine sizes, specifically the V6 EcoBoost offerings in the F150

Yep. I owned and liked the 2.7, a real workhorse for the small displacement. Whether it will last for 150K, well, ??
The 5.0 V8 guys all prefer their mill but they don't have the hp or tq of the 3.5.

 

[theblet]

I’m happy with my 5.7 with 3.21. Plenty of power to pull many things.

 

[bwsRam19]

I'm happy with my 5.7 with 3.92. More power to pull more things.

 

[jimchi]

I'm happy with my 5.7 with 3.92. More power to pull more things.

Technically, since this is an "engineer's guide" and I am a pedant, it's the same amount of power. You probably mean "More torque to pull more things."

 

[Buz]

Technically, since this is an "engineer's guide" and I am a pedant, it's the same amount of power. You probably mean "More torque to pull more things."

Opening a BIG can of worms are you? lol
Both have the same HP and Torque. The only difference is the time it takes to hit those numbers when you hit the gas.

 

[jimchi]

Opening a BIG can of worms are you? lol

Yes. My work here is done.

 

[silver billet]

Opening a BIG can of worms are you? lol
Both have the same HP and Torque. The only difference is the time it takes to hit those numbers when you hit the gas.

Not really; the 3.92 will multiply the engine torque/hp more than the 3.21 will in first gear. But I refuse to fixate on that one number, a truck is all about balance and compromise; 1500's shouldn't be pulling > 8000 pounds anyway IMHO.

 

[Willwork4truck]

Yes. My work here is done.

We used to call them folks “shyt disturbers”...

 

[ChryslerVette]

I rarely tow trailers, and when I do they aren't heavyweights. Therefore, gear ratio is less important to me than the fact it has a limited slip or not for winter traction.

 

[Sportznut]

To the OP - Thanks for the data and explanation.

It is great to deal in facts but too much work and not as much fun as spewing baseless opinions.

25 pages of comments and counting - the 3.21 vs. 3.92 debate is a passionate one. I have owned both. Like them both for different reasons.