|
11-15-2012, 04:07 PM
|
#1
|
Rivet Master
1986 34' Limited
1975 27' Overlander
1969 21' Globetrotter
Conifer
, Colorado
Join Date: Jun 2009
Posts: 8,315
|
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
|
|
|
11-15-2012, 05:46 PM
|
#2
|
retired USA/USAF
2001 30' Excella
Somerset
, New Jersey
Join Date: Jan 2009
Posts: 2,418
|
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.
__________________
Roger in NJ
" Democracy is the worst form of government. Except for all the rest"
Winston Churchill 1948
TAC - NJ 18
|
|
|
11-15-2012, 08:12 PM
|
#3
|
2 Rivet Member
2010 27' FB International
Birmingham
, Michigan
Join Date: Jan 2010
Posts: 62
|
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.
|
|
|
11-15-2012, 08:26 PM
|
#4
|
USN/LAPD Retired
2005 25' Safari
North Las Vegas
, United States
Join Date: May 2005
Posts: 850
|
Ditto !
__________________
2007 Dodge Ram Quadcab 6.7L Diesel w/jakebrake
"Better to have more then you need, then need more then you have because you don't have enough!"
AIR #: 8129
|
|
|
11-15-2012, 08:28 PM
|
#5
|
USN/LAPD Retired
2005 25' Safari
North Las Vegas
, United States
Join Date: May 2005
Posts: 850
|
Quote:
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
__________________
2007 Dodge Ram Quadcab 6.7L Diesel w/jakebrake
"Better to have more then you need, then need more then you have because you don't have enough!"
AIR #: 8129
|
|
|
11-15-2012, 08:37 PM
|
#6
|
Rivet Master
2007 28' International CCD
Springfield
, Missouri
Join Date: Apr 2011
Posts: 1,423
|
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.
|
|
|
11-16-2012, 03:40 PM
|
#7
|
Rivet Master
1986 34' Limited
1975 27' Overlander
1969 21' Globetrotter
Conifer
, Colorado
Join Date: Jun 2009
Posts: 8,315
|
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
|
|
|
11-16-2012, 06:04 PM
|
#8
|
Rivet Master
Hampton
, New Hampshire
Join Date: Oct 2005
Posts: 2,126
|
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.
__________________
Brad (The Slowsky's)
2019 Airstream Classic 30RBT, 2021 Ford F350 King Ranch 4X4 w/6.7L Diesel, Hensley, ACI #1313
travelwiththeslowskys.com
|
|
|
11-16-2012, 06:17 PM
|
#9
|
Rivet Master
2017 30' Classic
Loretto
, Ontario
Join Date: Oct 2010
Posts: 507
|
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.
|
|
|
11-16-2012, 11:01 PM
|
#10
|
Chief Chili Cook
2010 30' Flying Cloud
Bakersfield
, California
Join Date: Feb 2009
Posts: 738
|
Quote:
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.
__________________
The NSA -- The only part of the government that listens.
|
|
|
11-17-2012, 05:34 AM
|
#11
|
3 Rivet Member
1985 31' Excella
Seguin
, Texas
Join Date: Nov 2011
Posts: 113
|
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.
|
|
|
11-17-2012, 07:40 AM
|
#12
|
4 Rivet Member
1995 34' Excella
Corinth
, Mississippi
Join Date: Dec 2010
Posts: 304
|
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.
__________________
Why settle for anything less?
1995 34ft Classic Excella 1000
2012 Kings Ranch F-250 FX-4, 6.7 diesel, 6 speed auto trans.
TAC # MS-8
|
|
|
11-19-2012, 04:33 AM
|
#13
|
Rivet Master
1986 34' Limited
1975 27' Overlander
1969 21' Globetrotter
Conifer
, Colorado
Join Date: Jun 2009
Posts: 8,315
|
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
|
|
|
11-19-2012, 05:13 AM
|
#14
|
3 Rivet Member
2008 31' Classic
Lake Charles
, Louisiana
Join Date: Apr 2009
Posts: 153
|
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.
|
|
|
11-19-2012, 05:24 AM
|
#15
|
Rivet Master
2009 27' FB Flying Cloud
1982 31' International
1991 35' Airstream 350
Jay
, Oklahoma
Join Date: Oct 2006
Posts: 1,706
|
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
__________________
Jeff & Cindy
'09 27FB Flying Cloud;'82 31 International
'91 350 LE MH; '21 Interstate 24GT
|
|
|
11-25-2012, 10:25 PM
|
#16
|
Vintage Kin
Fort Worth
, Texas
Join Date: Nov 2006
Posts: 8,014
|
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.
.
|
|
|
11-28-2012, 08:04 PM
|
#17
|
Rivet Master
2002 30' Classic S/O
Garden Valley
, Idaho
Join Date: Jul 2010
Posts: 1,631
|
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
__________________
2008 F-250 4X4 Lariat V-10
2002 Airstream Classic 30' w/SO #2074
2007 Kubota 900 RTV
1996 Ford Bronco
2007 Lincoln LT
|
|
|
11-28-2012, 10:00 PM
|
#18
|
Rivet Master
2015 25' FB Eddie Bauer
2013 25' FB Eddie Bauer
2012 20' Flying Cloud
Small Town
, *** Big Sky Country ***Western Montana
Join Date: Feb 2010
Posts: 2,860
|
3.73 in our diesel and the AS disappears in the mirror ...
__________________
2015 25' Eddie Bauer Int'l FBQ / 2023 Ford Lightning ER
2022 Ford F350 6.2 V-8; equalizer hitch + Shocker air hitch
Honda Eu3200; AIR# 44105; formerly WBCCI 2015.1
Terminal Aluminitis; 2-people w/ 3+ dogs
|
|
|
12-09-2012, 03:33 PM
|
#19
|
Rivet Master
1986 34' Limited
1975 27' Overlander
1969 21' Globetrotter
Conifer
, Colorado
Join Date: Jun 2009
Posts: 8,315
|
3.31 with18" wheels versus 3.55 with 20" wheels
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
|
|
|
12-09-2012, 06:20 PM
|
#20
|
4 Rivet Member
2000 34' Excella
Tucson
, Arizona
Join Date: Apr 2006
Posts: 375
|
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.
|
|
|
|
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
|
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
|
Recent Discussions |
|
|
|
|
|
|
|
|
|
|
|