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Discussion Starter #1
I've seen people debate axle ratio and MPGs before and I was always convinced to get the taller gear( lower number) for better highway mileage because I do alot of it. 15-20K/year or more, a lot of it unloaded. but I plan on keeping my truck 10+ years and I don't know if I'll ever need the extra 1-2,000lbs of towing the lower gear provides. So I finally sat down and and did some math:

This assumes 150,000 highway miles over the life of the truck which if you keep the truck 10+ years is not unreasonable to see that many highway miles, I focused on this because lower gears(high numbers) usually get better mileage in the city anyway.

Diesel @ 3.60/gal
@28mpg; 150k miles / 28mpg = 5357 gallons x 3.60/gal = $19,285

@27mpg; 150k miles / 27mpg = 5555 gallons x 3.60/gal = $19,998

@26mpg; 150k miles / 26mpg = 5769 gallons x 3.80/gal = $20,768 Total Difference $1,483


Diesel at $3.80/Gal
@28mpg; 150k miles / 28mpg = 5357 gallons x 3.80/gal = $20,357

@27mpg; 150k miles / 27mpg = 5555 gallons x 3.80/gal = $21,111

@26mpg; 150k miles / 26mpg = 5769 gallons x 3.80/gal = $21,923 Total Difference $1,566


Diesel at $4.00/gal
@28mpg; 150k miles / 28mpg = 5357 gallons x 4.00/gal = $21,428

@27mpg; 150k miles / 27mpg = 5555 gallons x 4.00/gal = $22,220

@26mpg; 150k miles / 26mpg = 5769 gallons x 4.00/gal = $23,076 Total Difference $1,648



If someone had shown me that we'd be done. ~$1,500 over 150K miles/10 years is something I can live with. I've completely changed my stance from getting 3.55s to now getting 3.92s
 

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I like the math, but I don't need it to convince me of the rear-end choice. I think the 8-speed auto with double overdrive gearing makes the rear-end choice a no-brainer :)
 

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Discussion Starter #4
Yes it will. Which is why lower geared vehicles usually get better city mileage.
 

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wont the 3.92 walk out of the hole better as well? I'm going off my ranger fx4 with 4.10 vs ranger 4x4 with 3.55....

Turbo engines are different and I have no experience with a diesel however I did turbo a gasoline Dodge Slant 6 and learned a lot with that combo.

Started with 3.23, then 2.94 and finally settled on 2.76. In each instance it went faster with new gearing. Torque is huge, best run is a 11.02 @ 121mph and could go on a 1,000 mile road trip now if needed. Turbo's like load and this translates to boost and torque.
 

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Wow, I consider 15-20k/yr to be "average" mileage. I hit 9 years with my truck next week, and I'm about to roll 250k on the odometer, so by the time I hit 10 years I'll probably be at 280k or so. I hit 150k before the truck was 5 years old!!!

Amazingly (I guess), I've had no power train issues - engine, trans, transfer all original. I do change fluids (fairly) regularly, and oil/filter every 3k like clockwork.......

Did have to put bearings in the rear end about 25,000 miles ago, but that's not too bad.

I hate to think about how much I've spent in fuel though.......at an average of *maybe* 15 mpg (and that's likely a bit optimistic) and an average of $3.50 a gallon.........well, way more than I paid for the truck anyway.....:eek:
 

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The thing to remember is turbo diesels are torque makers/monsters.
Keep the revs low, let the torque do the work.
 

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Typo and question

I've seen people debate axle ratio and MPGs before and I was always convinced to get the taller gear( lower number) for better highway mileage because I do alot of it. 15-20K/year or more, a lot of it unloaded. but I plan on keeping my truck 10+ years and I don't know if I'll ever need the extra 1-2,000lbs of towing the lower gear provides. So I finally sat down and and did some math:

This assumes 150,000 highway miles over the life of the truck which if you keep the truck 10+ years is not unreasonable to see that many highway miles, I focused on this because lower gears(high numbers) usually get better mileage in the city anyway.

Diesel @ 3.60/gal
@28mpg; 150k miles / 28mpg = 5357 gallons x 3.60/gal = $19,285

@27mpg; 150k miles / 27mpg = 5555 gallons x 3.60/gal = $19,998

@26mpg; 150k miles / 26mpg = 5769 gallons x 3.80/gal = $20,768 Total Difference $1,483


Diesel at $3.80/Gal
@28mpg; 150k miles / 28mpg = 5357 gallons x 3.80/gal = $20,357

@27mpg; 150k miles / 27mpg = 5555 gallons x 3.80/gal = $21,111

@26mpg; 150k miles / 26mpg = 5769 gallons x 3.80/gal = $21,923 Total Difference $1,566


Diesel at $4.00/gal
@28mpg; 150k miles / 28mpg = 5357 gallons x 4.00/gal = $21,428

@27mpg; 150k miles / 27mpg = 5555 gallons x 4.00/gal = $22,220

@26mpg; 150k miles / 26mpg = 5769 gallons x 4.00/gal = $23,076 Total Difference $1,648



If someone had shown me that we'd be done. ~$1,500 over 150K miles/10 years is something I can live with. I've completely changed my stance from getting 3.55s to now getting 3.92s
In your first block of numbers you mistyped 3.80 which should be 3.60 but the math is right.

Question. If I am going to be using this truck to tow a travel trailer, what gear ration would you recommend is best for that?
 
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