Although perhaps valid for general comparisons, please be aware that manufacturers' "trailer tow ratings" contain the following traps:
1. The trailer tow rating is calculated by subtracting the truck's curb weight from its GCWR (gross combined weight rating). The curb weight is unrealistically low since it is typically based upon a base truck (no options or accessories) with only a 150 lb driver. The actual laden curb weight (LCW) of a truck with driver, passengers, full fuel tank(s), accessories (including 5th wheel hitch, toolboxes, etc.), options, cargo, pets, etc. can vary by 1000 lbs or more from the manufacturer's curb weight used in this calculation. The actual equation that should be used to avoid exceeding the truck's rated GCWR is:
Truck's GCWR - Truck's LCW = Maximum allowable total weight of loaded trailer
2. The manufacturers' trailer tow ratings don't take into account the GVWR of the truck. Only in the fine print does one find the admonition that "no ratings of the truck should be exceeded (i.e., GCWR, GVWR and GAWRs)" when towing a trailer. This is especially important when selecting a tow vehicle for 5th wheel trailers that can carry 20% or more of their total weight on the truck as pin weight where it counts against the truck's GVWR. This is where the higher GVWR of the dual rear wheel truck comes into play as a single rear wheel truck will typically exceed its GVWR before approaching its GCWR or "manufacturer's trailer tow rating" when towing a 5th wheel. The formula for calculating maximum allowable pin/hitch weight without exceeding the truck's GVWR is:
Truck's GVWR - Truck's LCW = Maximum allowable pin/hitch weight of loaded trailer.
A conservative approach when shopping for a 5th wheel is to use the RV's GVWR as the total loaded weight and 20% of the RV's GVWR as the pin/hitch weight to compare with the results in the equations above.
2016 Ram Longhorn 3500 Dually 4x4 CCLB, 385/900 Cummins, Aisin AS69RC, 4.10
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