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Discussion Starter #1
I’m looking at ordering a Tradesman with the 17’s and am trying to decide which gear ratio. I’ve decided against the Outdoorsman pkg since I don’t really care about some of the stuff and a “loaded” Tradesman will give me everything I want except the 32gal tank and extra HD shocks.

The LT265/70R17E OWL On-/Off-road tires are 31.6” tall. The P275/60R20 BSW All-Seasons are 33” tall.

The mpg and towing reviews on the internet seem to be with 3:55’s and 33” tires since they all have the 20” rims. I’ve read one review where they had the 3.92s and mpg was about 2 miles less on low and high ends. This was with the 20/33’s.

It seems that with the 17”rims/31” tires and 3.92’s it’d be quite a bit lower geared. But we have the 8speed tranny.

Would the 17/31’s with 3:55’s be about the same as the 33’s and 3.92’s?

I’m not so sure I want to loose 2 or 3 mpg by going with 17/31’s. My TT is full size but only about 5000 wet and fully loaded. I’m also gonna haul a 700lb atv in the bed. I’ll be at max payload I know but that’s the way it goes. I’ll be using the truck as a car most of the time, more than towing.

3:55’s or 3.92’s with the 17/31 wheels and tires??
 

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Wow, sounds like you will be over payload. Let me know how that goes.

I don't know what the terrain is where you live, and how often you will tow, but I would pick what is easiest on the drive train, and that is the 3.92s.
 

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I wouldn't worry too much about going 3.92 gearing. Our 8 speed tranny is going to save you in the fuel department. I have a 2012 BMW 320i with the Zf 8 speed and it works wonders. Your tire size will matter much more than the gears. I would stick to 17" if I were you.
 

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The slightly smaller tires will not affect your mileage that much. but the taller gear (3.55) will net you a significant difference over the 3.92. my current truck has the 3.55 rear end with 17" rims but I run 285 tires. another factor in mileage is if you decide to put LT rated tires on (stock is P rated unless you go with the outdoorsman) your mileage will suffer a bit. LT's are a must for me as I am on back roads a lot. I also have a similar weight TT and will be putting air bags in the rear. my current truck has the coils in the rear an hauls like a pogo stick even with the weight distribution hitch and nothing but a cooler in the bed.
 

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Man I don’t know either, :confused: in 8th gear (.67):

3.55/20s:
1900RPM is about 78MPH
70MPH is about 1700 RPM

3.92/17s:
1900RPM is about 68MPH
70MPH is about 1960 RPM

3.92/20s, or a bit larger tires on the 17’s:
1900RPM is about 71MPH
70MPH is about 1875RPM

I’m thinking 3.73s would be ideal, I do not believe the 3.55/3.92s were chosen by RAM with this diesel/trans in mind. (3.55 for max mileage I suppose, but notice you can’t get 3.21s) If you plan on running larger than stock tires 3.92s are the way to go I believe.
 

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Discussion Starter #6
Thanks for the input guys. A few comments regarding some of yours.

According to RamTruck builder and the brochure the LT265/70R17E OWL On-/Off-road tires are available as an option on the Tradesman, only other availability seems to be the Outdoorsman. I need LT's for sure with our roads up here. We still have a couple dirt highways plus frost heaves, etc.

Payload.... ug... I wish Ram would fix the lousy gvw/payload ratings on these trucks. The QC 4x4 Tradesman with the diesel is 6950 and 1400. Ford F-150 STX S-Cab is 7350 and 1830.

It's just the wifey and I but 500lbs tongue weight plus WD hitch, 700lbs of atv, 125lbs of wifey and a 15lb dachsund some road grub and I'm at 1400!! I'm thinking some airbags or the air suspension but I don't think I'm ready for the air suspension in this Arctic environment. Rather, I'm not sure the air suspension is ready for Arctic after reading this... 2013 Ram 1500 Air Suspension problems when -10 or lower - DODGE RAM FORUM - Ram Forums and Owners Club! - Dodge Truck Forum

I'm thinkin that with 3:55's and 8 gears the tranny should do a good job of keeping the engine in the powerband pulling 5000 with or without the atv in the bed. Plus a guy can lock out higher gears can't you? But on the other hand, down the road it's easier to go with a larger tire than to swap out gears. Plus, according to Ram, the 3.92's adds 1000lbs to GVWR and Max towing.

Then again, 3.92's empty will turn higher rpms so running empty mpg will suffer some. But, either way, it'll beat the Hemi! :D
 

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Snyd, what kinds of roads will you be running on up there? Flat highway at 70+, or 2-lanes at 65-, hills etc? If you are going slower with hills/curves you might want to think about the 3.92s. We need some of the guys who ordered 3.92s to chime in when they get their rigs.
 

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I have run the numbers, every possible tire and RPM, and posted on the topic... if you are towing, probably 3.92... but I'll probably go with the 3.55 and 17" wheels. 3.92 would work fine, but I will not be towing anything more than 6000 pounds, and if I do, I'll borrow my old 2006 Ram-Cummins from my nephew.
 

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Discussion Starter #9
Snyd, what kinds of roads will you be running on up there? Flat highway at 70+, or 2-lanes at 65-, hills etc? If you are going slower with hills/curves you might want to think about the 3.92s. We need some of the guys who ordered 3.92s to chime in when they get their rigs.
More like 2 lanes a 45-60 mph. Some areas of 65mph speed limit flats. Your thinking is what I was considering. Quite a bit 45-50 up and down up and down with lots of curves, at those speeds 3.92's sound good but I'm coming from old school, 4spd man or 3spd autos! Now we've got this 8 spd in the mix. My current tow rig is an 88 Chevy van with a 350 built up, custom exhaust, TH400 with a shift kit and 3.73's. Obviously not hauling at atv. Back in 91 I pulled a 32ft TT up the ALCAN with my 79F150 short box, bored and stroked 351, 4spd with 3.50 gears and 32" tires.

Might consider a trip though Canada down to America some day.
 

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Discussion Starter #11
Let me know when the SIlvers are running, may take a trip up !
Marsman
:D ahhh, silvers. I used to go fish em in Valdez in August. For eating I prefer the Copper River Reds. Wifey and I just got done eating on one tonight! Might have to hit Valdez again though. Problem is, I'm Sheep Huntin in August! That's my first passion.
 
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