
Selecting the appropriate trailer for a job depends on towing vehicle, payload, and coupling. Each has limiting factors that affect how much a work truck can haul without suffering damage or compromising the driver’s ability to control the load.
How Much it ALL Weighs
As the acronym implies, gross combination weight rating (GCWR) is the total weight of work truck, passengers and cargo, plus the trailer and its cargo. The rating is developed and managed by the U.S. DOT’s Federal Motor Carrier Safety Administration and applies to complete vehicles like pickups and vans, not trucks built from an incomplete chassis.
Based on drivetrain, engine, transmission, number of drive axles, axle ratios, and braking capability, the chassis manufacturer provides GCWR for conventional coupling devices (ball-and-socket hitches attached to truck’s rear) and fifth-wheel/gooseneck coupling devices (attached to top of chassis near rear axle).
Vehicle manufacturers test chassis towing and stopping capability before determining GCWR.Look for GCWR in the vehicle’s trailer towing guide or specifications.
Trailer Weight and Payload
Another acronym comes into play: trailer gross vehicle weight rating (GVWR).
GVWR is the weight of the trailer plus its payload. Manufacturers must consider axle(s), tires, frame, coupler, and safety chains to determine a product’s rating.
Look for the rating on the trailer’s certification label; typically, a metal plate welded or riveted to the left front side of the trailer. The label’s required by the National Highway Traffic Safety Administration, so if it’s missing ask the seller where it is.
Keeping the Connection
The coupler is a series of components -- receiver, draw bar, hitch ball, and connecting pin – that connects the towing vehicle and trailer. Manufacturers follow SAE International (formerly, the Society of Automotive Engineers) standards based on type.
· SAE J684 Trailer Couplings, Hitches, and Safety Chains-Automotive Type http://standards.sae.org/j684_200507/ applies to trailers with 10,000 pounds and under GVWR. These are ball-and-socket hitches that attach boat, camping, travel, utility, and other special-purpose trailers to cars, light-duty commercial vehicles, light trucks, and multipurpose passenger vehicles and are divided into four classes:
· Class 1 for trailers not to exceed 2,000 pounds· Class 2 for trailers over 2,000 pounds and not to exceed 3,500 pounds
· Class 3 for trailers over 3,500 pounds and not to exceed 5,000 pounds
· Class 4 for trailers over 5,000 pounds and not to exceed 10,000 pounds
Some manufacturers market Class 5 hitches up to 17,000 pounds even though SAE J684 doesn’t have such a rating.
· SAE Recommended Practice J847 Trailer Tow Bar Eye and Pintle Hook/Coupler Performance Doesn’t specify classes like the more common ball-and-socket hitches, but provides a performance test for manufacturers to ensure ring-and-pintle and clevis-and-pin hitches and draw bars perform to rated test capacities.
· SAE J2638 Fifth-Wheel/Gooseneck Attachment Performance Up to 30,000-lb Trailer Gross Vehicle Weight
Putting It All Together
This is where things get a bit complicated because it involves yet another acronym: the work truck’s GVWR.
You can’t rely solely on the truck manufacturer’s GCWR. The rating includes the trailer’s weight but not the truck’s chassis, body, equipment, passenger, fuel, and whatever the trailer’s hauling. The difference is how much payload you can safely tow.
For example, let’s say a truck with 26,000-pound GCWR and 19,000-pound GVWR is loaded to its full GVWR. Even if the manufacturer says the truck’s maximum trailer weight is 11,000 pounds, in this case it’s actually 7,000 pounds.
Finally, a note about the coupling’s impact on all this: It’s determined by the system’s weakest component. If the hitch is rated at 10,000 pounds but the hitch ball is rated for 9,000 pounds, maximum towing capacity is 9,000 pounds. Don’t tempt fate by loading up beyond that.