Preposterous as it may seem, until recently there was no legitimate means of comparing the trailer-tow rating advertised by one truck manufacturer with claims issued by competitors. That created a game of leap-frog. With the introduction of every new large truck, the proud manufacturer would announce some new high in the number of pounds that could be hauled or towed. That would prompt one or more competitors to pause for a few months before announcing revised tow ratings for their products which would of course return their progeny to the top of the towing heap.
But after years of effort, the SAE's tow vehicle trailer rating committee is finally ending the farce. The SAE's Surface Vehicle Recommended Practice J2807 spells out in precise terms a procedure for determining two important ratings: the maximum permissible gross combination weight (GCWR) for a tow vehicle and its trailer and the maximum permissible trailer weight rating (TWR).
After three years of effort by the three domestic manufacturers and representatives from several of the Japanese brands, a standard was approved in April 2008 and scheduled for 2013 model year implementation. Some companies have already begin phasing in the more realistic J2807 tow ratings for their new models.
There are five engineering characteristics that strongly influence any tow vehicle's performance:
- The engine's power and torque characteristics.
- The powertrain's cooling capacity.
- The durability of the powertrain and chassis.
- Handling characteristics during cornering and braking maneuvers.
- The structural characteristics of the vehicle's hitch attachment area.
Standard J2807 spells out test procedures and performance requirements that must be meant for a manufacturer to assign a maximum tow rating to a particular vehicle. While various trailer configurations are suitable for these tests, the towed unit must provide a minimum specified frontal area starting with 12 square feet for a TWR below 1500 pounds, ranging to 60 square feet for a TWR exceeding 12,000 pounds. There are also specifications for how the trailer's load is distributed on its axle(s) and how the attachment tongue is configured.
One major change from past practice is what the SAE committee defines as Tow Vehicle Trailering Weight (TVTW). Unlike the past, a driver, a passenger, optional equipment purchased by at least one third of the customer base, and hitch equipment are now included in this calculation along with the base weight of the tow vehicle. Raising the TVTW figure automatically lowers the maximum permissible GCWR and TWR figures.