Originally Posted by lee cole
whats the correct formula for tow weight
There is no such thing as a good formula for estimating the max trailer weight of a tandem-axle travel trailer (TT). My tow vehicle, for example, has a tow rating of 8,400 pounds, but I'm overloaded with my TT that grosses 4,870 when wet and loaded on the road. That's 58% of Ford's advertised tow rating.
My previous tow vehicle was an F-250 diesel with tow rating over 13,000 pounds. But it was overloaded with my small 5er that grossed only 8,000 pounds when wet and loaded on the road. That's 61.5% of Ford's tow rating.
But I'm not going to suggest that 58% or 61.5% is a good formula for others to use.
Instead of picking a number out of the air, you need to know the weight of YOUR
tow vehicle when wet and loaded for the road before you tie onto any trailer. Wet means a full tank of gas, and loaded means with all the people and other things that will be in the tow vehicle when towing, including the weight-distributing hitch, campfire wood, tools, and options such as a bed liner.
Subtract the weight of your wet and loaded tow vehicle from the GVWR of that tow vehicle and the answer is the maximum tongue weight of any TT you can tow without being overloaded.
(The maximum tongue weight is also called the available payload capacity of your tow vehicle. There is probably a payload capacity number on the doorframe of your tow vehicle, but no, you cannot use that number either, because it is not the available unused payload capacity of your wet and loaded tow vehicle. So you must weigh the wet and loaded towvehicle to determine the real-world payload capacity available for tongue weight.).
Divide that maximum tongue weight by 0.125 and the answer is the maximum GVWR of any TT you want to consider. Or if you want to be conservative and almost guarantee you won't be overloaded with a TT that is not overloaded, then divide the maximum tongue weight by 0.15 instead of 0.125. Tongue weight of an "average" wet and loaded TT is about 12.5%, but max tongue weight of many TTs is about 15% of wet and loaded trailer weight.
And don't try to guess at the wet and loaded trailer weight. Use the GVWR of the trailer as the probable max trailer weight you'll have in the middle of your third RV trip.
Sorry to bust your fantasy of a simple formula to determine the max weight of any TT you might want to tow. But the simple facts of life is that there is no such formula.