kittyjo
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3.21
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3.21. vs 3.92 gear
- Thread starter Mike97
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With 3.21 I’m around 1500rpm. Maybe a little less
gbsharrock
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Which line in the incoming from the transmission?
Richard320
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I paid close attention on a recent long trip, remembering this post.
At 70 mph with 3.21 gears and 275/65R18 tires, closer to 1500 than 1750 so I'd call it 1600 RPM in 8th.
I bought a 5th gen off the lot with the 3.21 gear ratio on it, and 22 inch tires. I was looking to go with larger tires (maybe LT285/50r22) which are obviously heavier and than stock, and a diameter of 33.5”. Will this kill my performance drastically? I don’t tow and run mostly highway, but cannot stand the 285/45r22’s. Looking for some insight. Has anyone put larger tires on a truck with a 3.21 gear ratio?
ExcursionDiesel
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That stock tire is around 32". Going to a 33.5 tire is not a huge change. Less than 5%. Go for it...if it fits without rubbing.
Jako
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Don't know if this helps at all but somewhat interesting.
Tire Size Calculator
The best tire size calculator. Use our tire size calculator to find tire size specs and suggested tire sizes. Then check prices for all available tire sizes.
silver billet
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I haven't done the math; but I put 1 inch bigger and much heavier tires on my old Jeep GC which had a horrible gear ratio (3.12? 3.09??) and only 5 gears, which weighs almost as much as my truck and had the same v6 pentastar. Could not notice the change by my butt dyno.
The hemi has so much torque I'd eat my hat if you would notice any difference. Just by a pedal commander or something to even out the difference
mp1
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I haven't done the math; but I put 1 inch bigger and much heavier tires on my old Jeep GC which had a horrible gear ratio (3.12? 3.09??) and only 5 gears, which weighs almost as much as my truck and had the same v6 pentastar. Could not notice the change by my butt dyno.
The hemi has so much torque I'd eat my hat if you would notice any difference. Just by a pedal commander or something to even out the difference
Good to know. I have 3.21 with 32" tires and plan on getting 33.5" soon
I know going from 32" to 33.5" will drop the effective gear ratio down from 3.21 to 3.06. So when is a gear ratio too low?
Hemiguy226
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??! I don’t get those miles on same truck
Bainers
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He lives in a different kind of city
silver billet
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Neither does he. Not with those conditions.
I just bought a 2022 Big Horn with the 3.92. I test drove a Laramie with the etorque 5.7l with 3.21 then got in the Big Horn 5.7l (non etorque) with 3.92. It didn't even seem like the same truck to me. The Big Horn was so much quicker. Plus, towing 11,400 compared to the Laramie at 8,300. I'll eat the extra couple miles per gallon to have such a drastic increase in performance.
silver billet
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It's important to remember that something can "feel" faster, without actually being faster; in this case, because the 3.92 shifts from first into second at a lower MPH than the 3.21 does, it feels like it's accelerating quicker. It shifts faster because the gear is shorter, not because the engine is working all that much easier. If you put 18 gears in that thing it will rip through them in a heartbeat and maybe give you that impression of really working hard/fast, but it's not. "So much quicker" is simply inaccurate.
When you do 0 to 60 runs in both trucks, the 3.92 will be slightly faster, but how much? What are the actual differences? I can't seem to find any reliable test that compares otherwise equivalent trucks, but this test compares pretty close trucks, and shows the results are measured in a few tenths of a second:
3.92 vs 3.21 Who Wins? TruckTrend data shows...
- Accel 0-60 MPH 3.92- 6.94 secs; 3.21- 6.44 secs
- 1/4 Mile 3.92- 15.93 secs @ 91.13 MPH; 3.21- 15.71 secs @ 92.97 MP
- Accel 0-60 (Towing 7,500 lb weight) 3.92- 14.28 secs; 3.21- 14.48 secs
- 1/4 Mile (Towing 7,500 lb weight) 3.92- 20.23 secs @ 72.57 MPH; 3.21- 20.30 secs @ 72.95 MPH
- Tested Fuel Econ (Average/Best) 3.92- 14.50/17.96; 3.21- 15.73/19.07
0 to 60 the 3.21 was a half second quicker. And look at the 1/4 mile while towing 7500 pounds... apparently it really can't tow 3000 pounds more than the 3.21 despite the paper certification that it can, which is what I've been saying all along. So while the 3.92 may give the impression of being significantly faster to some people, most of that is simply a "feeling" and not actually measurably different with a stop watch.
The poster in that thread noted that the trucks are not otherwise equivalent, slightly different weights and tire sizes too. Ok, so if the 3.92 took a slight hit from tire size (though it's also 118 pounds lighter than the 3.21) then why did it go faster 0 to 60 while towing but get less MPG? This is my point, in acceleration it's pretty much equal or a wash, but when you're daily driving this thing and paying todays gas prices... well I'll take the 2 mpg gain they got with the 3.21.
If you guys can find other comparisons please post them, the more data we have the better.
It's important to remember that something can "feel" faster, without actually being faster; in this case, because the 3.92 shifts from first into second at a lower MPH than the 3.21 does, it feels like it's accelerating quicker. It shifts faster because the gear is shorter, not because the engine is working all that much easier. If you put 18 gears in that thing it will rip through them in a heartbeat and maybe give you that impression of really working hard/fast, but it's not. "So much quicker" is simply inaccurate.
When you do 0 to 60 runs in both trucks, the 3.92 will be slightly faster, but how much? What are the actual differences? I can't seem to find any reliable test that compares otherwise equivalent trucks, but this test compares pretty close trucks, and shows the results are measured in a few tenths of a second:
3.92 vs 3.21 Who Wins? TruckTrend data shows...
www.ramforumz.com
- Accel 0-60 MPH 3.92- 6.94 secs; 3.21- 6.44 secs
- 1/4 Mile 3.92- 15.93 secs @ 91.13 MPH; 3.21- 15.71 secs @ 92.97 MP
- Accel 0-60 (Towing 7,500 lb weight) 3.92- 14.28 secs; 3.21- 14.48 secs
- 1/4 Mile (Towing 7,500 lb weight) 3.92- 20.23 secs @ 72.57 MPH; 3.21- 20.30 secs @ 72.95 MPH
- Tested Fuel Econ (Average/Best) 3.92- 14.50/17.96; 3.21- 15.73/19.07
0 to 60 the 3.21 was a half second quicker. And look at the 1/4 mile while towing 7500 pounds... apparently it really can't tow 3000 pounds more than the 3.21 despite the paper certification that it can, which is what I've been saying all along. So while the 3.92 may give the impression of being significantly faster to some people, most of that is simply a "feeling" and not actually measurably different with a stop watch.
The poster in that thread noted that the trucks are not otherwise equivalent, slightly different weights and tire sizes too. Ok, so if the 3.92 took a slight hit from tire size (though it's also 118 pounds lighter than the 3.21) then why did it go faster 0 to 60 while towing but get less MPG? This is my point, in acceleration it's pretty much equal or a wash, but when you're daily driving this thing and paying todays gas prices... well I'll take the 2 mpg gain they got with the 3.21.
If you guys can find other comparisons please post them, the more data we have the better.
Any data for something more realistic than 0-60 or 1/4 mile? Any data comparing two otherwise identical trucks?
Last edited:
Where you seeing 2mpg difference? The data you provided shows basically only 1mpg difference in both average and best. Of course, you can take truck trend performance testing with a grain of salt. It's rarely accurate comparisons. I actually participated in one of their track days many years ago with a group of Dakota R/Ts. The day we were there, the track was not prepped at all, we were actually kicking up clouds of dust going down the track. Air temps were over 100 degrees. They told us they would make sure to note the temperature in the article and post "corrected" times as well as actual. When the article was released, no mention of the heat effecting our times, and they even went as far as to comment about how much slower our trucks were than when they did a similar thing with Ford Lightnings, when the air temp for them was in the 70's.It's important to remember that something can "feel" faster, without actually being faster; in this case, because the 3.92 shifts from first into second at a lower MPH than the 3.21 does, it feels like it's accelerating quicker. It shifts faster because the gear is shorter, not because the engine is working all that much easier. If you put 18 gears in that thing it will rip through them in a heartbeat and maybe give you that impression of really working hard/fast, but it's not. "So much quicker" is simply inaccurate.
When you do 0 to 60 runs in both trucks, the 3.92 will be slightly faster, but how much? What are the actual differences? I can't seem to find any reliable test that compares otherwise equivalent trucks, but this test compares pretty close trucks, and shows the results are measured in a few tenths of a second:
3.92 vs 3.21 Who Wins? TruckTrend data shows...
- Accel 0-60 MPH 3.92- 6.94 secs; 3.21- 6.44 secs
- 1/4 Mile 3.92- 15.93 secs @ 91.13 MPH; 3.21- 15.71 secs @ 92.97 MP
- Accel 0-60 (Towing 7,500 lb weight) 3.92- 14.28 secs; 3.21- 14.48 secs
- 1/4 Mile (Towing 7,500 lb weight) 3.92- 20.23 secs @ 72.57 MPH; 3.21- 20.30 secs @ 72.95 MPH
- Tested Fuel Econ (Average/Best) 3.92- 14.50/17.96; 3.21- 15.73/19.07
0 to 60 the 3.21 was a half second quicker. And look at the 1/4 mile while towing 7500 pounds... apparently it really can't tow 3000 pounds more than the 3.21 despite the paper certification that it can, which is what I've been saying all along. So while the 3.92 may give the impression of being significantly faster to some people, most of that is simply a "feeling" and not actually measurably different with a stop watch.
The poster in that thread noted that the trucks are not otherwise equivalent, slightly different weights and tire sizes too. Ok, so if the 3.92 took a slight hit from tire size (though it's also 118 pounds lighter than the 3.21) then why did it go faster 0 to 60 while towing but get less MPG? This is my point, in acceleration it's pretty much equal or a wash, but when you're daily driving this thing and paying todays gas prices... well I'll take the 2 mpg gain they got with the 3.21.
If you guys can find other comparisons please post them, the more data we have the better.
silver billet
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Fair enough, it's all I could find. I think if you read these MPG threads long enough we can see at least 2 to 3 mpg difference on average, the more highway travel you do the more the difference. My personal best is 25 mpg all highway.
We can pick apart testing methodology all day long, this test will have flaws just like every other test. The point is to look at what the data is suggesting: no difference in acceleration or for towing, but the more you travel on the highway (unloaded/not towing) the more you save with the 3.21's MPG.
How can I say this? Because nobody does 0 to 60 all day long, that's the only time you might see a few tenths of a difference, when you are running flat out. But we often sit on the highway or rural roads for hours at a time, and the 3.21 constantly benefits at those times; we're running at 400 rpms lower.
Here in Canada we'll see gas prices hit $2.00/L by summer. I spent $125 for my last fill up at $1.52/L so doing the math, that will cost me $165 by summer. Nobody buys a truck to save gas, but if you need a truck I don't see the point in spending extra for something that I'll never need (drag racing points).
A lot depends on where you drive as well. Live in an area with long flat roads, sure. Only makes sense the 3.21 will do better of fuel mileage. Get in an area with lots of hills, or mountains, I bet the difference narrows significantly as the 3.21 will be shifting a lot more often.
silver billet
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I wish I could find a test, but I haven't yet.
silver billet
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All the 3.92 does, is take the same 8 gears and move them down 1 rung. You gain an extra first, and lose the 8th. So that means there is no difference in shifting patterns, unless the 3.21 is in 8th and can't hold that gear at which point it will downshift to 7th.
Since the entire point of the 3.21/8th gear is fuel economy, I'll take that extra shift. With the super smooth 8 speed and the difference being 400 rpms, its not noticable at all, and if you happen to hit that rare road and wind condition and speed where you find yourself downshifting more than normal, just use the gear limiter. I haven't ever done that yet in my almost 3 years of ownership.
