Words by Mike Levine, Mark Williams and Kent Sundling, Photos by Ian Merritt
Davis Dam Grade Climb
After nearly four years of deliberation and negotiation, truck manufacturers and the Society of Automotive Engineers are expected to agree to the industry's first tow testing standards for pickups by late this year.
The standard, known as J2807, establishes tow-vehicle performance requirements against the following criteria to establish maximum ratings: timed acceleration on level ground and up a 12 percent incline; maintaining speed on a real-world grade; understeer; trailer-sway response; braking and park brake at gross combined weight; and tow-vehicle hitch/attachment structure. To minimize test variations, J2807 provides standard test trailer specifications and requirements for use in these tests.
Once J2807 is implemented, truck buyers will finally have an apples-to-apples comparison for the trailer-towing capacity of all light-duty pickups. All manufacturers are expected to follow it starting with the 2013 model year. PickupTrucks.com is using parts of the standard for testing, including the standardized hill climb at Davis Dam Grade.
Topographical map of Davis Dam Grade based on GPS data collected by our VBOX and exported to Google Earth. The red line representing our timed course starts at the upper right (near the Colorado River) and finishes 59,000 feet (11.17 miles) later in the lower left at Union Pass.
The Davis Dam grade test site is on U.S. Highway 68, just outside Bullhead City, Ariz. We started our run at the intersection of Highway 68 and McCormick Boulevard, the same place that J2807 specifies. The top of the grade is about 12 miles from the starting point. We measured 11.17 miles (59,000 feet) from start to finish, just past the Union Pass marker at the summit. The incline is a steady 5 percent for nearly its entire length.
Each truck had two clean runs up the grade at wide open throttle from start to finish. Runs during which the driver let off the accelerator, braked or both were not counted. The trucks were in tow/haul mode, with the exhaust brakes on and the air conditioning set to maximum for the entire climb.
The first run was completed late in the afternoon. The second run was completed the next morning. We averaged the two runs to calculate the fastest time.
Despite the grade’s length and the hot temperatures, which we thought would expose and exaggerate any weaknesses in cooling or power, all of the trucks were very competitive.
The Ford F-350 and GMC Sierra sparred fiercely with each other for the fastest time. The Ford was fastest on the first run and the GMC was fastest on the second. GMC’s average time up the hill was 11.5 seconds faster than the Ford’s time. The Ram 3500 finished just more than a minute behind the F-350.
This chart shows each truck's speed climbing Davis Dam Grade against the clock at wide open throttle. The GMC Sierra 3500's fastest run was 671.3 seconds, the Ford F-350's best time was 710.8 seconds and the Ram's quickest climb was 774.2 seconds. The sloped lines represent each truck's position climbing the mountain.
This chart shows the speeds of the three trucks relative to each other over the 59,000 foot (11.17 mile) run to the top of Davis Dam Grade. Note how similar the speed patterns are for each truck as the grade changes throughout the climb.
The GMC Sierra 3500’s quickest time up Davis Dam was 11 minutes, 11.3 seconds, and its average speed pulling from 500 feet up to 3,000 feet in elevation was 58.35 mph. Top speed was 69 mph for a few moments where the highway’s slope decreased to 3 percent for several hundred yards.
The Ford F-350's best time up the grade was 11 minutes, 50.8 seconds at an average speed of 54.9 mph. Its top speed was 63.15 mph.
The Ram’s fastest run was 12 minutes, 54.2 seconds at an average speed of 50.64 mph. Its top speed was 62 mph, at the same spot the GMC and Ford hit their top speeds.
Of the three trucks, the Sierra ran coolest up the hill, even when the outside temp was more than 100 degrees. Coolant temp climbed by just 3 degrees, from 187 to 190, and transmission temp ranged from 210 to 215.
While the Ford was almost as fast as the GMC, its powertrain ran hotter. Coolant peaked at 231 degrees, and the transmission temp hit as high as 216. The Ram stayed cooler than the Ford but warmer than the GMC. Coolant temp topped out at 226 degrees, and the transmission hit 213.
All the trucks’ engine fans turned on during their runs to cool things down, but the Ram’s fan was the loudest. The Ram also had the roughest shifts and seemed to have difficulty figuring out whether to stay in 3rd or 4th gear, hunting for a sweet spot among the two gears.
It’s worth noting that all three trucks would have easily passed the SAE J2807 minimal speed standard, which is 35 mph on Davis Dam Grade for a dually one-ton pickup with a gross vehicle weight rating of 13,000 pounds or less.