Originally Posted by thehallocks
So please help this old fart out and set me straight in plain laymens English.
Hi Tom -
It's reasonably simple, but not as simple as you'd like it to be.
There are two weight ratings for your tow vehicle that you need to understand.
GVWR is the limiter on most pickups and SUVs with single rear wheels (SRW). That's the max weight, including hitch weight, you can haul
on the 4 truck tires without being overloaded. But ignore the payload rating of your tow vehicle (TV), because it's not even close to accurate.
The only way to determine your max hitch weight is to load the truck down with all the people and stuff that will be in it when on the road. Stuff includes pets, tools, jacks, cooler, and options you added, such as spray-in bedliner and trailer hitch. For a TT hitch, you want to include the shank and ball mount for the weight-distributing hitch. For a 5er hitch, you want the whole shebang installed in your truck, or at least loaded into the back of the truck. Then go to a truckstop with a CAT scale, fill up with fuel, and weigh the wet and loaded TV.
Subtract the weight of the wet and loaded TV from the GVWR of the TV, and the answer is the max hitch weight you can have without being overloaded.
TTs have anywhere from about 12 to 15 percent hitch weight, so to be safe, divide the max hitch weight by 0.15 and the answer is the max GVWR of any TT you can tow without being overloaded.
Smaller and medium-size 5er RVs less than 12,000 pounds have anywhere from 16 to 20 percent hitch weight, also call "pin" weight or kingpin weight. So to be safe, divide the payload available for hitch weight by 0.20 and the answer is the max GVWR of any 5er you can tow without being overloaded.
GCWR is the gross combined weight of the truck and trailer. That indicates the max weight you can pull
up a normal interstate grade at a reasonable speed without burning up something in the drivetrain. The tow rating is simpy the GCWR of the truck minus the dry empty "shipping" weight of the truck. It's overstated by at least 1,000 pounds for most vehicles, and ignores GVWR (hitch weight). So it's not useful for anything more than a wet dream of how heavy a trailer you can tow.
So compute you own realistic tow rating. Subtract the weight of the wet and loaded TV from the GCWR, and that's one limit as to how much trailer you can tow without being overloaded. But don't use that limit unless it's less
than the max trailer weight computed above, based on the GVWR of your TV.
Then realize that all this estimating might still get you in trouble if you don't frequently weigh the wet and loaded rig on a CAT scale. Add the weights on the 4 truck tires, and compare the total to the GVWR of the TV. Compare the gross weight of the truck and trailer to the GCWR of the TV. Compare the weight on the trailer tires to the combined GAWR of the trailer.
A dually might not have any more GCWR than an SRW, but it will have a lot more GVWR, so it can safely handle a lot more hitch weight.
An SUV can rarely get even close to the tow rating, because folks tend to haul more weight of people inside the SUV. So same rule if you have an SUV = subtract the weight of the wet and loaded SUV from the GVWR to detrmine the max hitch weight you can add without being overloaded. Then convert that available hitch weight into the max weight of any TT you can tow without being overloaded by dividing it by 0.15.
Note that TT sellers will tell you to use 10% to estimate hitch weiight of a TT. Don't believe them. My new 2012 TT has a hitch weight over 15%.