Advice on 2012 Ford Super Duty Diesel Axle Ratio

[dbj216]

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

[polarlyse]

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.

[Aquabud]

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.

[Safari-Rick]

Ditto !

[Safari-Rick]

Originally Posted by polarlyse

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

[Moflash]

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.

[dbj216]

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

[nilesrob]

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.

[Naper]

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.

[newroswell]

Originally Posted by dbj216

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.

[Pileus]

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.

[Hodum]

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.

[dbj216]

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

[Steve & Mary]

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.

[jdalrymple]

I have towed with 2 Duramax trucks, and loved them both. Both rear-end gears were 3.73.

The major difference is the transmisson in the '12 is a six speed. That brings the cruise RPM down to around 1800 at 70 mph.

I do hate the DEF issue, but I guess the folks at the EPA like having all the air scrubbers driving around. So we can have more iceburgs, of course.

Regards,

JD

[slowmover]

I wouldn't sweat 3.31. I intend to change my 3.73 manual transmission DODGE to 3.42. I don't mind going a bit slower from a stop or on ascents, and the gear ratios would allow me to otherwise (solo) to stay closer to peak torque in most situations (better mpg).

These trucks are all over-powered. Mine as much as yours despite the differences when it comes to pulling any size A/S.

Put your reading, instead, to a PRO PRIDE hitch and TT disc brake conversion.

.

[pappy19]

3.73 all the way. I would have a 4.10 if they offered it but they don't. Most come with a 3.55 but you can find a 3.73 if you look hard. Ford wants more higher rear end ratios as it shows up better on their emissions(lower the number, the higher the ratio). Mileage is a wash between the 3.73 and the 3.55. Higher than that and you loose power but gain mileage, but also more strain on the tranny. Your choice.

Pap

[mefly2]

3.73 in our diesel and the AS disappears in the mirror ...

[dbj216]

I thank you Airstream truckers for your descriptions of your experience. I did some thinking on this axle ratio business. Tire Rack has a great website that gives tire size diameters. 275/70R18 tires are 33.2 inch diameter resulting in 627 revolutions to travel a mile, 275/65R20 tires are 34.1 inch diameter resulting in 610 revolutions per mile. The Super Duty transmission top gear is .67 to 1 overdrive. So 3.31 axle ratio results in a 2.21 overall ratio, and 3.55 axle results in 2.38 overall ratio.

The 3.31 gears with 18 inch wheels gives 1386 engine rpm at 60, and 3.55 gears with 20 inch wheels gives 1452 rpm at 60.

Diesels don't have throttles. I probably have to feed the same fuel at 1386 rpm as I would at 1452 rpm to maintain 60 with the Airstream behind me.

I think I am fussing about nothing. Either combination would result in the same performance.

David

[elolson]

Dude I read the posts. No one mentioned that the new 2012 Ford diesels are spec'd at *800 ft-lbs* and 400hp. That is way over the top of what they have been the last few years. Airstreams are light in the big picture of 40' 5th wheels etc and the other junk people tow. Get some nice tall gears and enjoy the fuel mileage and cruising along. I have a 34' excella and had a Dodge cummins 3.73 with the factory 600ft-lbs. That towed just fine all conditions. I now have an '02 7.3 ford (550 ft-lbs with a standard) with 4.10 gears. It also tows fine and I wish I had 3.55s.