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Discussion Starter · #1 ·
Hi.
I have a dually 4 Speed AT 4wd longbed.
I have a guy who said I could go from 12 MPG to 18 MPG if I switch my axle ratio from 4:10 to 3:55.
I would love to get some comments on this. I’m still waiting to see how much it will cost. Are there other downsides to doing this? He said he can reprogram the speedometer so that it is accurate. Thanks.
 

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You're talking a small difference.
But you have to consider tire size too.
Go with overdrive and have the cake and eat it too.
If you google your question and filter the emotion the 4;10 is the deal
On the flats, you could drop 500 RPM with an OD unit, but doing it with the final drive is prolly not ideal.
 
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Discussion Starter · #3 ·
You're talking a small difference.
But you have to consider tire size too.
Go with overdrive and have the cake and eat it too.
If you google your question and filter the emotion the 4;10 is the deal
On the flats, you could drop 500 RPM with an OD unit, but doing it with the final drive is prolly not ideal.
Thanks. It has an overdrive button in the gearshift and I run it on overdrive all the time and my RPMs are still too high even on the flats. At 60 miles an hour and my RPMs are 2000. I’m told my RPMs should be closer to 1200 or 1300 at 60 mph
 

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Do you still tow that truck camper? if so, your going to hate 3:55. Gross, 3:55??? At least 3.73. Dont destroy your towing power for a little mpg. might as well buy a f150.

Also 12 to 18 mpg? I'm calling BS there. You might, I mean "might" see 2mpg, but most of that depends on how you drive. MPG is so damn subjective, anyone that makes a claim like that is being ignorant.
 

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The factory OD is probably a 75% unit, you need a ger vendors or simular
 

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Discussion Starter · #7 ·
Do you still tow that truck camper? if so, your going to hate 3:55. Gross, 3:55??? At least 3.73. Dont destroy your towing power for a little mpg. might as well buy a f150.

Also 12 to 18 mpg? I'm calling BS there. You might, I mean "might" see 2mpg, but most of that depends on how you drive. MPG is so damn subjective, anyone that makes a claim like that is being ignorant.
I won’t be towing anything. But I will be carrying a 4 to 5000 pound truck camper in the bed. Since I’m at 2000 RPMs at 60 mph I am told that changing the axle ratio to 3:55 I should be able to be at about 1300 RPMs at 60 mph which would be significant fuel savings. So I’m told.
 

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Words are EZ, and results are much more difficult.

Your best results will vary from platform to platform with dependencies on many many factors.
The coefficiency of a camper on a truck going dwn the road has to HIGH!
On a short vehicle, it might be more than the 70-foot semi-truck !
Have this person show you rather than be his experiment ....he must be speaking from experience, correct?
I am not believing it..
 
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4:10's = 2000RPM
3:73's = 1725RPM
Gear vendors is supposed to be a overdrive ratio of 0.78.
4:10's plus gear vendor = about 1375
 

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At 1300-1400 you'll be under the torque curve of the engine. you want to be 1600-2100, ideally.
your mpg's won't change much if at all. it's a calculation of wind drag. the 2K rpm's isn't bad, it's the Load on the engine that's the issue.
If all you do is 60 mph then yours good, if you want to go 70, then 3.73 are the ticket.
i do not believe you'll see any savings on fuel. just a lighter pocket book.
 

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Is MPG your main concern, or are you wanting to be able to go 60+ without screaming down the road over 2000rpm? As stated above, lots of variables in play here, but any regear will be costly and likely take a long time to recover your investment via gains in fuel efficiency. IMO at your GVCW 3.55 gears would be just fine, but again costly. And I doubt you’d average 18mpg, unless you did some really fine tuning with a quad and even then the conditions would have to be right.
 

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2022 RAM 5500 Tradesman Crew Cab & Chassis 4X4
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I have a guy who said I could go from 12 MPG to 18 MPG if I switch my axle ratio from 4:10 to 3:55. I would love to get some comments on this.
If he told you wolverines made great housepets.......would you believe that as well?

There‘s not a gear swap out there for a 2nd GEN RAM that will net a 50% increase in fuel economy.

Ask your “guy” if he will put his money where his mouth is.....and eat the gear swap cost for you if it doesn’t add 6 MPG......
 

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Some improvement is likely, but not that much. All else being equal, just 4.10 to 3.55 would likely be 2-4mpg better at 55 mph, At 55 mph Tach wold be about 1500rpm and about 3-400 less than 410. Speedo does not care what gears are in it as it just counts revelations. Changing tire size is what affects speedo and odometers and can only be partially corrected depending on year.
You will loosed considerable heavy towing power with that gear swap.
Cost can be 1000-2000 bucks per end. Tire tread make a significant difference in mileage. So does being a dually, and more important speed and driving habits. Anything over 55 can drop it fast.
 

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Discussion Starter · #17 ·
At 1300-1400 you'll be under the torque curve of the engine. you want to be 1600-2100, ideally.
your mpg's won't change much if at all. it's a calculation of wind drag. the 2K rpm's isn't bad, it's the Load on the engine that's the issue.
If all you do is 60 mph then yours good, if you want to go 70, then 3.73 are the ticket.
i do not believe you'll see any savings on fuel. just a lighter pocket book.
I was told that truck is at its best torque at 1200 RPMs
 

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Discussion Starter · #18 ·
Thanks everyone for your comments. I think I need to get out there and just see what kind of mpg I get going about 55 miles an hour. And go from there. normally I’ve been going a bit faster than that. But my wife and I are planning on doing some very long trips including going to Alaska, so I do want to get a handle on mpg.
 

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I was told that truck is at its best torque at 1200 RPMs
1200 RPM is lugging the hell out of it. Ideal range for power is 1600-2000.

Cruising under 2000rpm, you will maybe see 18mpg unloaded with a dually depending on driving style, but with a camper? Never!
 

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Yeah, you want to be cruising @ 1800-2000ish RPMs range. That's the sweet spot for these trucks. Somewhere close to 65MPH depending on your final drive ratio. Tire size and final drive ratio have the biggest impact to MPGs. Took me a while to learn this from others.
 
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