The towing standard, called SAE J2807, tests vehicles under load in three categories: climbing, acceleration and launching.
The tests are pass-fail, and the load weight is up to the manufacturer. If a pickup passes all three tests with, say, a 10,000-pound load, the truck gets a 10,000-pound rating.
In the launch test, a pickup with a loaded trailer is put on a steep 12 percent grade -- a rise of 12 feet over 100 feet of road. That's the equivalent of a 220-foot ascent in a half mile.
To pass, the pickup must travel uphill at least 16 feet from a standstill five times within five minutes, then do the same in reverse in another five minutes.
To pass the acceleration test, the vehicle and loaded trailer have 12 seconds to reach 30 mph and 30 seconds to reach 60 mph on level ground. The vehicle also must accelerate from 40 mph to 60 mph in less than 18 seconds on level ground.
The climbing test requires the vehicle and loaded trailer to ascend 3,000 feet over an 11.4-mile stretch without dropping below 40 mph and with the air conditioning at maximum. The test is based on the Davis Dam grade, a stretch of Arizona road southeast of Las Vegas.