3.21 vs 3.92

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jasonw

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An an aside, Scientifically proven dCt that a tonneau doesn't at all help with mileage. In fact it hurts.

I have ready studies that have gone both ways. Consumer Reports reported that a tonneau hurt MPG worse than with the tailgate down (and we all know how much faith we can put into some Consumer Reports "tests" sometimes), while SEMA reports that a tonneau decreases drag by 4.2-7.8%. Mythbusters was right in the middle, saying tonneau covers didn't hurt or help, but were better than having the tailgate down.

It supposedly also depends on your truck configuration/trim (long box vs short box, single cab vs crew cab, etc. etc.), so real conclusive testing would be very hard to do.

But back to the topic at hand... if towing any big loads regularly, go 3.92s. If towing mild loads (or a medium load every once in a while), and you want the best MPG in-between (when load-less), go 3.21s. If you plan on going bigger tires, 3.92s would probably be better, although its not the end of the world if you don't.
 

Smokey613

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Our recent vacation trip where we were "stuck" doing about 60 for over 60 miles.
 

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N1ck

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I was thinking the same... I have a lowered 2016 REG cab with 32" street tires and my 3.92 geared 8 Speed would never see 27mpg lol

Best I see is around 23MPG when cruising around 60.
 
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coldfusion73

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I have 3.92 and DD my truck. It's good on every day traffic. At 60mph I'm still pulling 27mpg. Any faster it goes down but even at 75 I'm still getting 19mpg. Can't say mpg for towing but I'm looking at getting a pop up and the 3.92 is rated around 10k lbs over 8k with the 3.21 gears. I plan on lifting and 35s. That's honestly why I got the 3.92 anyways. I'm hoping that brings the mpg in the higher speeds back a little like if I had 3.21s


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Is that with the pentastar?


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Cmsharp

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I have a 3.21. Evic said 20mpg for about 300 miles of driving to/ from work. About 60/40 highway/city. But hand calculated showed it at 18.3 mpg so my evic is definitely off!
 

ColdCase

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I have a 2016 SBRC with 3.21s and a tonneau. This is a interstate trip from Boston to Lexington towing a 14 foot cargo trailer with 6000 pounds on the way out and empty on the way back. MPG towing full was roughly 13 and the V8 didn't struggle but rpms reached 4500 driving up some of those WV hills. A nice sound :) Empty roughly 17mpg. I typically get around 20 when not dragging something. All EVIC numbers. Except for the steeper hills, I didn't notice a trailer pull behind me. And that was only because the transmission shifted and rpms increased. I'm sure at some weight 3.92 would be prudent.
 

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goldtr8

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My Hemi in my Charger can get close to 30 mpg on the highway if I play real nice with it.

My 1500 if I super baby it I can squeek 19 out of it driving back roads around 45 mph. Real numbers are always around 17 ish towing 8 to 10.
 
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