3.55 vs. 3.92 - MPG vs. Towing Ability - Ram 1500 Diesel Forum
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post #1 of 22 Old 08-19-2014, 11:52 PM Thread Starter
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3.55 vs. 3.92 - MPG vs. Towing Ability

Hi All,

Iím trying to decide on the best gears for my future purchase. Iím trying to see how big of a difference the gears make on the gas millage. That always seems to be the information people leave out of their MPG reports.

Also I have read several threads talking about towing more than the truck is rated for but they typically leave out what gears they have.

To me the gears are a huge part of evaluating the MPG and the towing ability.
Can some of you guys please clue me in on your experience with these two topics and let me know what gears you have?

Thanks!
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post #2 of 22 Old 08-20-2014, 01:21 AM
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i have limited experiance with towing above the rating. I have the 4x4 3.55 gears and it hauls my 3K LBS boat just fine. Cant tell its there.

3.55= better gas milage less pulling power
3.92=better pulling less MPG.

If you plan on towing 9k on a regular basis then get the 3.92. honestly at that weight you wont be getting great milage anyway. I tow once a month or 3 time if i am lake happy during the summer. 3.55 makes sense. I use the truck as a daily driver most of the time.
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post #3 of 22 Old 08-20-2014, 09:04 AM
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Just my .02. I ordered 3.55. I do 85% driving and tow the occasional "normal" trailer (utility trailer with dirtbikes or a quad, 25' camper, 19' boat) a total of 15 to 20 times a year combined. Nothing I have is over 5500 lbs. I went with the 3.55s based on the percentage of time I don't trailer anything. The question you need to ask yourself is how often and how heavy will you be? I've read threads were guys only lose 1 mpg hwy with the 3.92s. Good luck!
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post #4 of 22 Old 08-20-2014, 10:08 AM
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You are getting some good advice. Listen. My choice was 3:55's. Not disappointed as I haven't towed above 6,000 lbs and doubt I will ever get above 8K. No issues.

Oh - no "gas" mileage on a diesel. Now start to think "fuel" mileage and "fuel" stop.
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post #5 of 22 Old 08-20-2014, 04:53 PM
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A buddy of mine was giving me crap about the lower tow capacity, & my question to him was "how many times since you have owned your truck (3+ years) have you been over even 75% of the 10,400 lb tow capacity"?....His response, "probably never". My point exactly. This is why the ED is such a beautiful thing.....A family vehicle with a bed and hitch. I do way too much non towing / hauling to deal with 16-17 mpg! It all comes down to personal needs.
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post #6 of 22 Old 08-20-2014, 10:36 PM Thread Starter
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Thanks for all of your replies!!

So here is my issue,
I have a 5500 pound tractor (including attachments) and a 2500 pound trailer so I will be pushing the upper limit of it's rating. That being said, I'll probably tow it less than 5 times a year. Typical trip would be about an hour with mostly expressway driving. Possibly a 5 hour trip once every couple years.

Other than that and towing a couple 4 wheeler's the truck will be a daily driver for me. That's my dilemma, sacrifice the better mileage day to day so that I can tow a little easier a few times a year.

The laramie limited towing capacity is 7350 with 3.55 gears and 8350 with 3.92 gears

What would you do 3.55 or 3.92?
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post #7 of 22 Old 08-20-2014, 11:35 PM
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Oh boy....you are right on the bubble. Technically you would be over those few times a year, but I'm sure the 3.55s would work. Really with that weight I'd be more concerned with suspension sag. I'm not towing heavy, but for the price I've already purchased a set of air lift air bags. They are supposed to be good for a 1000 lbs. They help with sag, bounce, and some say sway. I've never used em but for under 100 bucks I figured it would be a nice add on. I'd like to hear someone chime in on difference in mpg. If it's minimal maybe 3.92s won't be a bad fit for you since you actually pull something that's heavy. Do the math once. Figure 1 mpg less over say 50000 miles and see what the 3.92s would actually cost you. If it's not much it may be a good option for you.
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post #8 of 22 Old 08-20-2014, 11:39 PM
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I just did a quick math work up....24 mpg average over 50k miles @ 3.69 a gal compared to 25 mpg is about a 300$ difference over those miles. If it's only 1mpg, I'd say go with 3.92s. But again I do not know if that is an accurate estimation in fuel economy.
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post #9 of 22 Old 08-20-2014, 11:55 PM
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Transmission section. ...axle ratio vs. Mpg....Some additional information there. It's like anything else. Many different opinions and at the end of the day you are just as confused as you were prior to asking the question. Ha. It sucks I know! In my opinion if it's a minimal gap ( 1 mpg or less) go with 3.92s. Just remember the more fuel costs the more that 1mpg loss will cost you. Really tho 300 bucks over 50k miles @ 3.69 isn't too bad.
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post #10 of 22 Old 08-24-2014, 10:04 AM
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Go with the 3.92's... The 8 speed has high enough gearing and overdrives to make up for it. 3.92's will give you better all around performance

2014 RAM 2500 BIGHORN 4x4
6.7L CUMMINS TURBO DIESEL
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