Extreme Traction Control Test
To complement the autocross, we also conducted an extreme traction-control test that examined how well the trucks could recover from a loss of grip. We placed the trucks’ right and left wheels on different surfaces with different amounts of friction — dry asphalt and wet basalt tile on a steep, 20 percent grade — to create a “split-mu” condition. Wet basalt has a coefficient of friction similar to a snow-covered road. This caused the trucks to slip to one side because the tires couldn’t gain traction equally. We parked each truck on the asphalt and basalt and attempted to drive off in two-wheel drive with traction control enabled.
Traction control cuts engine power when it senses wheel slip, allowing the slipping wheel or wheels to slow enough for the rubber to once again grip the driving surface. It may also use the truck’s antilock braking system to brake the wheel that’s spinning, allowing the wheel on the other side to grip. Because most full-size pickups are rear-wheel drive but have the bulk of their weight positioned in the front half of the vehicle, they can lose traction more easily than other vehicles, particularly in icy conditions.
The Ford F-150 and Toyota Tundra performed best. They were the only trucks to make it off the slippery surface without having to stop and engage four-wheel drive. The F-150’s traction was superior to the Tundra’s. While the F-150’s wheels did slip, the truck was able to cut throttle smoothly and apply selective braking until grip was restored and it was able to climb the basalt. The Tundra cut throttle too, but very aggressively. It took pushing the accelerator all the way to the floor to keep throttle up while the Tundra slowly crawled off the pad. Both the Tundra and F-150 had rear limited-slip differentials. They were also the heaviest trucks we tested, which likely helped.
The Chevrolet Silverado and GMC Sierra both had locking mechanical rear differentials that engaged automatically when wheel slip hit a certain rpm. While both pickups performed excellently in the autocross, they were challenged by the wet surface and fishtailed backward as power was applied. We had to put both trucks into 4-High to get off the basalt.
The Dodge Ram 1500 also required the use of 4-High to escape the split-mu surface, but like the F-150 and Tundra it has a rear limited-slip differential. To us, this was proof that extra weight and, particularly, excellent anti-slip logic can make a big difference getting a truck out of slick conditions.
The Nissan Titan was the most challenged by this test. When its electronic-locking rear differential wasn’t engaged (which only happens in four-wheel drive) the rear diff operated as an open differential, meaning there was no way to shift power or lock up the slipping wheel. The engine quickly hit close to the redline as the Titan slipped backward and struggled to figure out a way off the hill before we cut power and engaged four-wheel drive to escape.
Another traction-control test we conducted involved driving the trucks straight up a wet jenite surface without stopping. Wet jenite has a coefficient of friction similar to an icy road. Almost all the trucks were able to make it up the jenite as long as forward momentum was maintained at 10 mph or more. Again, the Nissan Titan was the most challenged by this test; it required backing off the jenite and using 4-High.
Next: Squat Test