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Old 11-15-2012, 05:07 PM   #1
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Advice on 2012 Ford Super Duty Diesel Axle Ratio

Will you experienced truckers give me some advice on the best axle ratio for my tow vehicle? I will be pulling a 34 Limited out west. The trailer weighs about 9800 loaded. The tow vehicle will also be used for errands and going to work. I was wondering if I could get by with a 3.31 axle ratio figuring the diesel has tons of torque down low, and the six speed ought to select the right gear for the load. And I figured traveling unloaded I could squeeze a little more out of a gallon of diesel with the higher axle ratio.

I am interested in the new Ford 6.7L diesel starting in 2011. I think 3.55 is the standard ratio, and wheel size may make a difference.

Will a 3.31 ratio be a mistake causing the transmission to shift down at every hill? Or maybe the diesel will be too low on the rev range and end up using more fuel that a guy would think.

Your experience towing with these newer Super Dutys would be welcome.

David
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Old 11-15-2012, 06:46 PM   #2
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I have a Dodge ram 3500 diesel and it came with the 3:73 rears. It pulls our AS 30'er and doesn't skip a beat. Sure it will downshift sometimes but I just set the cruise control and sit back and enjoy the ride. I think the ratio your talking about is fine unless you plan to tow mega-heavy loads through the rockies every day.
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Old 11-15-2012, 09:12 PM   #3
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I have a 2011 F250 with the 6.7 diesel. The gear ratios are set up so that towing is a breeze at near any speed. When towing, be certain to engage the Tow Haul button on the column shifter. This helps avoid multi-shifting during any elevation changing driving. If you're driving flat land slabs you can leave Tow Haul disengaged. I hardly ever notice the truck shifting even when driving through rain.
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Old 11-15-2012, 09:26 PM   #4
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Ditto !
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Old 11-15-2012, 09:28 PM   #5
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Quote:
Originally Posted by polarlyse View Post
I have a Dodge ram 3500 diesel and it came with the 3:73 rears. It pulls our AS 30'er and doesn't skip a beat. Sure it will downshift sometimes but I just set the cruise control and sit back and enjoy the ride. I think the ratio your talking about is fine unless you plan to tow mega-heavy loads through the rockies every day.

DITTO ! But, I have the Dodge 2500
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Old 11-15-2012, 09:37 PM   #6
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I have 355 gear ratio and you cannot tell a loaded 28ft trailer is attached.Taller gears would be fine with 10000lbs and mileage would benefit by them.
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Old 11-16-2012, 04:40 PM   #7
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So far I am hearing 3.31 axle ratio would be acceptable for the Super Duty diesel. I just didn't want lugging and shifting down too much. Like most of you, we will be towing our Airstream in the mountains as well as prairies.

Maybe someday there will be a two speed axle option for heavy duty pickups!

Anyone else with experience with conventional towing with high axle ratios and high torque diesels would be welcome.

Thanks,

David
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Old 11-16-2012, 07:04 PM   #8
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At the time I bought a new (right out of the wrapper) 2008 F250 6.4L diesel 4x4, and I don't know if it has a 3.xx axle ratio or a Waring Blender back there - no clue; I can only assume I have an axle, because the wheels turn when I step on the gas pedal. But over 100k miles it has towed magnificently, over mountain passes in Colorado and the Smokies, with very little shifting or anything to what I would consider outside of normal. And it drives great around town.
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Old 11-16-2012, 07:17 PM   #9
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I have a 2013 6.7 with 3:55. Couldn't ask for a better combination. 70 mpg at 1800 rpm no down shifting no matter the grade.
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Old 11-17-2012, 12:01 AM   #10
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Quote:
Originally Posted by dbj216 View Post
Will you experienced truckers give me some advice on the best axle ratio for my tow vehicle? I will be pulling a 34 Limited out west. The trailer weighs about 9800 loaded. The tow vehicle will also be used for errands and going to work. I was wondering if I could get by with a 3.31 axle ratio figuring the diesel has tons of torque down low, and the six speed ought to select the right gear for the load. And I figured traveling unloaded I could squeeze a little more out of a gallon of diesel with the higher axle ratio.

I am interested in the new Ford 6.7L diesel starting in 2011. I think 3.55 is the standard ratio, and wheel size may make a difference.

Will a 3.31 ratio be a mistake causing the transmission to shift down at every hill? Or maybe the diesel will be too low on the rev range and end up using more fuel that a guy would think.

Your experience towing with these newer Super Dutys would be welcome.

David
David, unless you (or the dealer) orders something special, you will get the 3.55 gears with the 20" wheels (34" tires). That is to put you back at the same ratio as the 18" wheels with 3.31 gears. I wouldn't try to out think Ford on this. If you get the 20" wheels (which is available a lot of different ways) take the 3.55 gears, if you go with the smaller wheels, take the 3.31 gears. 9800 is light for all these modern diesels.

We have the Lariat+FX4 package, so 20" wheels and 3.55 gears.
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Old 11-17-2012, 06:34 AM   #11
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If you get the 20" wheels, make sure the tires have the load capacity to handle a 34 ft. trailer and all your goodies (i.e. LT vs P series tires--hard to find in 20").
My truck has the 3.31 ratio, and I pull a 32 ft. I use the tow-haul mode, the 6-speed transmission selects the right gear for the load. It tows beautifully. Easily get 15 mpg.
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Old 11-17-2012, 08:40 AM   #12
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I had a 2011 F-250 with a 6.7 diesel and a 3:31 rear axle ratio. I could not have been better pleased with the way it preformed. I pulled my 34'ft air stream through the mountains of WV, VA, and East TN with no problems of excessive downshift. After a year of excellent service I went to the dealer and asked to trade for another truck exactly like the one I had except a year newer. They did not have it in stock so I traded for an upgrade Kings Ranch that had a 3:55 ratio rear axle ratio. the only difference that I can tell in performance is approximately 2mpg less when not towing and may be just a slight drop when towing. I could not be better satisfied with the performance of either truck, however i would prefer the 3:31 rear axle ratio after a year and 24,000 miles of driving it, many of which were towing.
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Old 11-19-2012, 05:33 AM   #13
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You experienced Airstream puillers are giving me some great advice. I am plannng on the F250 with the 18" wheels, and then opt for the 3.31 axle ratio. The Ford RV towing website does not degrade the towing capacity with this setup. I think I will have more relaxed cruising loaded or unloaded with the 3.31. I don't think the 3.31 is available with the larger 20" wheels. The desiel engine certainly has the torque to handle 3.31 even though I may loose a drag race with a Chevy truck now and then.

You folks have helped me make up my mind on this F250 option.

David
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Old 11-19-2012, 06:13 AM   #14
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We have a 2012 F-250 with the power stroke and 20 inch wheels. We love it. Pull a 31 Classic Limited and most of the time you have to remember the trailer is back there. Only issue I didn't like was the lack of fuel capacity when you are towing. I installed a Titan 50 gal. tank to replace the factory one. Haven't had a chance to tow yet but I'm use it is going to be a lot better since I'm not looking for fuel as often.
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