The Society of Automotive Engineers has updated its J2807 standards (Performance Requirements for Determining Tow-Vehicle Gross Combination Weight Rating and Trailer Weight Rating), and recommended this update be applied to all 2013 model-year trucks and SUVs with GVW of 13,000 pounds or less. As a result, more manufacturers are signing on, even though the process is voluntary, and by virtue of the often-stricter parameters in J2807, some tow ratings are going down. While most half-tons and 'utes will experience a drop of fewer than 500 pounds, if any, some single-rear-wheel HD pickups may drop more than 2 tons.
Much of this is because trucks like these equipped with diesel engines have the power, cooling, and potential braking capacity to haul a lot, and weigh less than dualies. But the single-rear limits rear-axle GAWR, and if a 20,000-pound tow rating has been calculated using a relatively light 15-percent hitch weight of 3000 pounds, the J2807 requirement of 20 percent (we like 20-25 percent for fifth-wheel and gooseneck hitches) drops that max fifth-wheel trailer to 15,000 pounds.