I have been reading the "Ford 2006 RV & Trailer Towing Guide and the F250 / F350 Super Duty Brochure". I am getting puzzled with some of the stuff I am reading.
Like this about the F350 4X4, Diesel, Crew, Short bed, SRW, suspension:
Front Axle (rating @ ground) 4 X 4 = 6000 lbs. F350 Rear Axle (rating @ ground) 4 X 4 = 7280 lbs. Max. Payload Wt. Rating F350 4 X 4 = 11400 lbs.
5th wheel towing Max. 15400 lbs.
My question is why is the so high? What is the relationship between axle ground rating and max. trailer rating? I am interested because I want to safely tow a 12,000 lbs 5th wheel with a pin around 1,700 lbs. and I would like to have some safety in the margins.
Will the single rear wheel provide this? I have read that with the Gross trailer Wt. above 10,000 lbs. one should go to Dual rear wheel or the larger trucks and beyond? If someone can point to an easy source to understand where these calculations are described I would really appreciate seeing that link or links.
I've seen very few people hit the axle ratings if they stay with the truck's vehicle weight ratings.
Ford's Guide computes the maximum towing weights based on a minimal truck, e.g., in the above case an XL trim truck without anything added. Moving up to a Lariat from an XL, and including a bed liner, tool box, etc., could add 1,000 pounds to the truck's weight. Two real limits on the maximum trailer weight exist, computed as follows.
The first limit is based on the trucks maximum gross combined vehicle weight limit (GCWR), which for an automatic diesel SRW F-350 is at least 23,000 pounds. If the truck weighs 8,000 pounds the maximum trailer weight is 23,000 - 8,000 or 15,000 pounds. This is close to Ford's number, and is how they get their maximums.
The other limit is the gross vehicle weight rating (GVWR), which limits the pin weight. This is the limit most fifth wheel and gooseneck rigs hit. An F-350 diesel SRW 4x4 LB has a GVWR of 11,500 pounds. If the empty wet truck weighs 8,000 pounds, the maximum weight of your payload, which includes pin weight, passenger weight, and the weight of everything else you carry, is 11,500 - 8,000 or
3,500 pounds.
If your pin weight is 1,700 pounds, everything else must weigh less than 3,500 - 1,700 or 2,200 pounds. Assume you carry four passengers at 175 pounds each, a hitch weighing 200 pounds, and another 300 pounds of cooler, tools, dog, etc., for a total of 1,200 pounds, and you are still 1,000 pounds under the truck's GVWR.
I will note that a 12,000 pound trailer's pin weight should be between
15% and 25% of your trailer's weight, or between 1,800 and 3,000 pounds. Your 1,700 pound pin weight seems low. Using 20% of the trailer weight on the pin, which gives a pin weight of 2,400 pounds, you're only 300 pounds under the truck's GVWR.
If the truck actually weights 8,300 pounds wet and empty, rather than
8,000 pounds, and we use 20% pin weight, you've hit the GVWR. Or if the weight of the trailer rises much, e.g., after you've stocked it and filled the tanks, the pin weight rises and you're again approaching the GVWR.
When I read people's comments about SRW vs. DRW, most who have towed with both say the DRW is much better, not because of the weight ratings but because of better stability and handling. For the above truck the DRW's GVWR is 13,000 pounds, an increase of 1,500 pounds but the truck weighs an additional 200 pounds. The DRW would provide a net 1,300 pounds of additional payload, a more comfortable margin than the SRW's 300 pound margin.
I think you need at least an F-350 DRW truck to get the margin you need. Could you get by with an F-350 SRW? Probably.
You'll find lots of good information, including this sort of discussion, over on
Funny thing is is that the 350 SRW and DRW have the same rear axle (except for hubs) and chassis so the two most important parts od combo are the same (both axles are rated at around 8500lbs) The difference is the tires and springs and if you increased the springs a bit and tires size the SRW will carry the weight fine. Some swear by duals for a bit more stabily and "image" but it is not the must have that some claim and if you are splitting hairs for max MPG towing you will do better with a SRW than a DRW model. Around here BP uses single tires replacements for duals on tractors and trailers because it reduces rolling resistance and if the oil company does it that tells you something too because they are looking for maxiumum frm their products. ALso you will have no more "reserve" in actual axle capacity with a DRW than a single if they have proper springs and tires otherwise and if you want to play the max GCW game the SRW truck will will less than a DRW one with any given payload too. I own a SRW 1 ton truck and never which it was aDRW and I have been glad many times that it is not.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.