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Old 07-22-2020, 05:22 PM   #1
Rivet Master
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Axle ratios

We're temporarily off the road, and I'm starting to seriously look for a pickup. We've narrowed things down to 2013-2017 Ford and RAM diesels, mainly because of a relationship with the local dealer. What rear axle ratios should I prefer? Which ones should I avoid? This is the first time I've ever had to be concerned about that number. I know that the lower the number the better fuel economy but the poorer pulling power, and the higher the number the better pulling power but poorer fuel economy. What's the best compromise?
David Lininger, kb0zke
AIR 54240
Heartland mpg 181 (sold)
1993 Foretravel U300 (for sale)
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Old 07-22-2020, 05:34 PM   #2
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Axle ratio is only one part of the equation. tire size, transmission gearing and peak horsepower and torque will affect towing as much as axle ratio.
1977 Safari Land Yacht
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Old 07-22-2020, 08:26 PM   #3
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Agreed. Specifically, I'm looking at the diesel engine and automatic transmission versions of each truck. Most of what I'm finding are 4wd models. As I understand things, the original buyers can choose from several different rear ends to increase either pulling power or fuel economy. I suspect that most trucks, though, come with the standard one. This question is probably aimed more at the gearheads out there. For example, I'm looking at a pair of F250's. One has a 3.73 rear axle and LT235/85R16E tires. The other has 3.31 rear axle and LT265/70RX17E tires. Any preference just based on rear axle and tires?
David Lininger, kb0zke
AIR 54240
Heartland mpg 181 (sold)
1993 Foretravel U300 (for sale)
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Old 07-22-2020, 08:54 PM   #4
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Frankly, you won’t need to worry. Any 3/4 ton diesel can pull an Airstream with ease. The lower the axle ratio the less towing capacity, but the better the gas mileage. The higher the ratio the more towing capacity and less towing capacity. If you can find one with a 3.2 to 3.5 I would go with that. Unless you are pulling something 15,000lbs or more you don’t need anything different. I would go with the 3.31 for an Airstream; better gas mileage.
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Old 07-22-2020, 09:16 PM   #5
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My 12 Ram 3500 came with 3.73 gears and my 18 Ram 3500 came with 3.42s. The 18 has more power and gets 50% better fuel economy. (The Big 3 truck companies seem to be making them more and more efficient.).

I agree, ANY 250/2500 can tow an Airstream snd the newer the better.
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Old 07-22-2020, 09:39 PM   #6
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Mono City , California
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The 2013 to 2017 Ford 6.7L Diesels are having failures of the High Pressure Fuel Pump
CP-4. Check out this problem on the internet. The Cummins in the Ram use a different High Pressure Pump and are not having failures. The CP-4 pump was used on the Duramax from 2011 to 2016 and are failing. Cost of repairs for the failure runs from $10,000 to $15,000.
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Old 07-23-2020, 05:10 AM   #7

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Zanadude Nebula , Milky Way
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Axle ratios today are a lot less important, they are just one part of the powertrain.
The engineers have done a much better job of designing the powertrain to optimize economy & performance.
You have a lot of ratios with an 8,9 or 10 speed transmission.


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"It is more wiser to ponder all things with diligent suspicion, than follow with blind assumption."
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