everyone hate there 3:21 gears?

[theblet]

Nope. I get 16-16.5 in the city.

If you are getting 18 city, it's not because of 3.21 gears, it's your eTorque.

Or both

 

[Mountain Whiskey]

Yet I get 18 in the city, you?

Yea, so does a 1977 VW Rabbit but the homeless guy pushing a shopping cart will pass it.

 

[Rick J]

What I hate.....


Every time this thread gets bumped to the top and I have to read the subject line and its improper use of the word there....

Sorry, couldn't resist.

 

[Ramroo]

Except the simple resistance of air has a 3.21 struggling to get that fast. 3.92 trucks just glide along.

Gotta glide when they run out of gas.

 

[Idahoktm]

Or both

Nah. I'm sticking with eTorque, unless you can explain how a truck with 3.21 gears is more efficient in the city.

 

[Rick3478]

Nah. I'm sticking with eTorque, unless you can explain how a truck with 3.21 gears is more efficient in the city.

The engine's internal friction and pumping losses probably come out in the wash if you assume the transmission will compensate and keep you in the "right" gear.

At low speed you may lose a bit by using the torque converter a fraction of a second longer.

A small amount of energy is dissipated by the shock absorbers on each acceleration from stop due to the twisting force applied to the rear axle by the driveshaft, and that force is smaller with the 3.92 gears.

So the 3.21 gears might actually be *less* efficient in the city.

 

[theblet]

Nah. I'm sticking with eTorque, unless you can explain how a truck with 3.21 gears is more efficient in the city.

Because rpm’s are lower in every gear with 3.21s. you probably won’t see much of a difference in bumper to bumper traffic tho.

 

[Idahoktm]

Because rpm’s are lower in every gear with 3.21s. you probably won’t see much of a difference in bumper to bumper traffic tho.

The RPM's will not be any different until you reach top gear and get past a certain speed. If you have the same driver in both trucks, the shift RPM's will be the same and at average speeds of ~ 35MPH, both trucks will be at the same RPM, even if they are in a different gear. A 3.92 geared truck is not going to hold a higher RPM than a 3.21 truck if another gear is still available.

 

[theblet]

1st and 8th should be different.

 

[Rick3478]

And while I'm at it - the increased twist applied to the rear axle by the lower gear ratio increases uneven tire wear. We really should get rid of that nasty old energy-wasting live beam axle differential thing and put on a good full independent rear suspension.

 

[Idahoktm]

1st and 8th should be different.

The TCM will still shift out of 1st gear at a certain RPM, no matter which gear set you have. At 35 MPH, the 3.21's would be turning 793 RPM's and the 3.92's would be turning 968 RPM's in 8th gear. I don't believe it's possible to hold 793 RPM's under a load.

Edit:
I just got back from an errand. The TCM won't allow the engine to drop below ~1,100 RPM's, so 8th gear isn't going to happen in normal city driving...at least where I live.

 

[BowDown]

Nope. I get 16-16.5 in the city.

If you are getting 18 city, it's not because of 3.21 gears, it's your eTorque.

I thought etorque provided minimal gains a\nd was BS? At least that's what I've read here, confusing.
BTW, there is no "if" I am getting that mileage, I posted a pic above along with a 5k mile average.

 

[BowDown]

Nah. I'm sticking with eTorque, unless you can explain how a truck with 3.21 gears is more efficient in the city.

Easy, lower rpm's. Less rpm's, less fuel burn.

ETA

https://www.ramforumz.com/attachments/drive-ratios-v2-pdf.35959/

That seems to disagree with your same rpm premise and I just looked at 3rd gear, look at the other 6. 3.21 truck is 1-3 mph in every gear, if you worked backward and matched the speed, the 3.21 truck is turning less rpm in every gear to achieve the same speed

 

[Av1]

I think the best gear ratio is the one that suits your needs most.

I have 3.92 gears which suit my needs because I have 35+ inch diameter tires. I live at a pretty high density altitude and drive through mountains with 8% grades to and from work.

If I had stock diameter tires in a predominantly flat area close to sea level, I would much rather have the 3.21 gearset unless I planned on towing heavy.

Neither gearset is a disaster in either situation, but one may be the better choice over the other depending how we use our trucks.

 

[Idahoktm]

Easy, lower rpm's. Less rpm's, less fuel burn.

ETA

https://www.ramforumz.com/attachments/drive-ratios-v2-pdf.35959/

View attachment 138870

That seems to disagree with your same rpm premise and I just looked at 3rd gear, look at the other 6. 3.21 truck is 1-3 mph in every gear, if you worked backward and matched the speed, the 3.21 truck is turning less rpm in every gear to achieve the same speed

At a steady speed of 35 MPH, the 3.92 truck will be in 7th gear at 1213 RPM's. The 3.21 truck will be in 6th gear at 1183 RPM's. 30 RPM's is not going to make any difference. In city driving, both trucks will spend most of the time accelerating, decelerating, and sitting at traffic lights. In that situation as well as steady speeds of 35 MPH, 3.21's have zero advantage. Even if the speed was bumped up to 45 MPH, a 3.21 truck could not hold 8th gear under a load. The truck would have to shift down to 7th gear at 1278 RPM's, while the 3.92 truck is in 8th at 1245 RPM's.



I don't like eTorque, but I never said a word about it not having an advantage in city driving. In heavy stop and go traffic, it could easily get 2 MPG better economy than the standard Hemi.

 

[BowDown]

At a steady speed of 35 MPH, the 3.92 truck will be in 7th gear at 1213 RPM's. The 3.21 truck will be in 6th gear at 1183 RPM's. 30 RPM's is not going to make any difference. In city driving, both trucks will spend most of the time accelerating, decelerating, and sitting at traffic lights. In that situation as well as steady speeds of 35 MPH, 3.21's have zero advantage. Even if the speed was bumped up to 45 MPH, a 3.21 truck could not hold 8th gear under a load. The truck would have to shift down to 7th gear at 1278 RPM's, while the 3.92 truck is in 8th at 1245 RPM's.

View attachment 138872

I don't like eTorque, but I never said a word about it not having an advantage in city driving. In heavy stop and go traffic, it could easily get 2 MPG better economy than the standard Hemi.

Then why am I at 18mpg and you at 16mpg?
I didn't say you made a negative comment about etorque, I said I've repeatedly read that here; not that the opinion of those making the comment matters to me, just pointing out the seemingly prevailing thought here about etorque.

Secondly, your chart or premise seems wrong, my truck (presumably all the 3.21 trucks too) doesn't even go into 8th until 54 mph. Using your steady speed of 35mph and my above chart, the 3.21 truck could be in either 6th or 7th, lets use your 7th gear reference, at around 900 rpm to make 35 mph. The 3.92 truck is at 1000 rpm is at 32 mph and would likely be at ~1100rpm to make 35 mph. That's a 300 rpm difference.

 

[theblet]

Man, I can’t wait to hit 2000 posts!

 

[bigdodge]

Man, I can’t wait to hit 2000 posts!

someone will just start another thread!

 

[Rick3478]

That seems to disagree with your same rpm premise and I just looked at 3rd gear, look at the other 6. 3.21 truck is 1-3 mph in every gear, if you worked backward and matched the speed, the 3.21 truck is turning less rpm in every gear to achieve the same speed

Missing the point, or distracting from it, that it *won't* be in the same gear at the same speed. The 3.21 truck will often be in a lower gear than the 3.92, until you top out at 8th.

 

[Mountain Whiskey]

Theoretical paper proof.

Just remember real life facts, not theory.

3.21=4g gears (girls grocery getter gears)

3.92 = MPT gears (Man's Powerful Truck)

Admittedly the head of the Federal Department of Energy did release a report recommending 3.21 gears though.