OK,
I've responded to these hitch threads a few times already, but here goes;
- The Society of Automotive Engineers (SAE) are the ones that come up with the hitch classifications. A Class IV hitch (such as the one that Dodge claims they install on our trucks) is rated by SAE at 500 lbs dead weight and 5,000 lbs towing capacity and 1,000 lbs hitch weight and 10,000 lbs towing with weight distributing bars. I did an extensive search a while back and can find no other criteria from SAE. I would agree that information is hard to find and sparse.
- From an engineering perspective the WD bars do a lot more than simply change the way the weight of the trailer tongue acts on the vehicle's suspension. They change the point loading on the hitch fasteners. As Rockcrawler has found out, WD bars change the way the hitch reacts to the tongue weight. Simply put, the hitch can handle more weight with the bars than it can without.
- Dodge claims the hitch is a class IV, but then claims a 12,000 lb tow capacity. These statements are contradictory as far as I can ascertain. Perhaps this is why not all of us got a paper raising the 10,000 lb limit to 12,000.
Ultimately if DC says we can tow 12,000 lbs with the truck using the factory hitch, then I'm sure it's OK, BUT I WOULD STRONGLY RECOMMEND THAT ANYONE WITH OVER 500 LBS TONGUE WEIGHT OR 5,000 LBS TRAILER WEIGHT USE THE WEIGHT DISTRIBUTING HITCH SET-UP. Maybe you can use your discretion and decide that 600/6000 is OK given DC's apparent upping of the Class IV ratings, but that's up to you.
My 2. 5 cents on the issue
Dave