Practically all towing guides give RVers just enough information that may cause them to purchase a trailer too heavy for their tow vehicle's capabilities. Towing guides listing TWR or Maximum Tow Capacity or Tow Limits fail to take into consideration the different towing capacity calculation requirements between 5th wheel and conventional trailers. These basic guides do not consider the additional weight created by the fifth wheel trailer kingpin. Then there is the problem of knowing the real tow capacity of a newly purchased tow vehicle after it is fully loaded with passengers, cargo, and other aftermarket accessories. Even the creators of the most well known towing guide published by Trailer Life use to devote four pages of instructions entitled "Choose Wisely," that spelled out the details required for selecting the correct towing combination.
"WEIGHT: The tow-ratings guide in this section lists the maximum tow ratings for vehicles with specific equipment, but many buyers interpret the maximum vehicles' tow ratings with far too much optimism. Always check the manufacturer's figures before making a purchase. The following is an explanation of the terms you need to know which, when combined with readings from a public scale and from your own calculator, should help you determine the correct tow rating for the tow vehicle you plan to buy." (emphasis added) Note: Trailer Life discontinued the article containing this quote beginning with the 2016 issue.
The RV Safety and Education Foundation (RVSEF) data indicates that 60% of all tow vehicles on the road exceed one or more weight safety ratings. "Many of these trucks exceed all of their ratings." (Walter Cannon, RVSEF Video, @14 minutes, 50 seconds)
None of the towing guide publications discuss the weight safety formula for calculating towing capacity based on available payload. The calculation for the available payload is a very important step, especially for 5th wheel trailers, to ensure the vehicle's weight safety ratings will not be exceeded. Since a majority of vehicle owners do not read and heed the instructions, cautions, and warnings in their owner's manual, the best choice to ensure total tow vehicle and trailer compatibility, is using the industry leading RV Tow Check app.
But for those who still insist on using these unrecommended towing guides, this resource will remain available. PDF reader required.
For more information, read this article "Before You Buy That RV, Truck or Other Tow Vehicle."