All-wheel-drive systems have come a long way from that first Audi Quattro, yet the Mazda's setup still shows evidence of the same philosophy. It begins with a new, compact, twin-shaft gearbox adapted to the transverse engine. This gearbox features a unique, water-cooled power take-off that spins a driveshaft connected to an electronically actuated clutch pack just ahead of the rear wheels. Finally, a torque-sensing, limited-slip differential distributes the power between the rear wheels themselves. The amount of torque that the fast-acting clutch pack transmits to the rear wheels is determined automatically by electronic data input from the steering angle, yaw rate, lateral g forces, and engine performance, and the torque distribution falls into three modes: normal, sport, and snow. The normal calibration distributes most of the torque to the front wheels with some directed to the rear wheels for stability, while the sport mode varies torque distribution front and rear according to acceleration and cornering inputs. The snow mode delivers a more constant distribution to all four wheels for optimum traction.
As you leave Mt. Whitney and follow U.S. Highway 395 farther north, you reach Lee Vining, on the shores of desolate Mono Lake. Here, Tioga Pass begins with California Highway 120, the first genuine road across the mountains. A trail initially blazed by the Mono Indians and then followed by mountain man Joseph Walker in 1833, Tioga Pass climbs the sheer rock wall of the Sierra. As you negotiate the last steep pitch, it's like entering a huge matte painting of Mordor as seen in the recent The Lord of the Rings trilogy. The road seems to go straight up into the sky, cresting at 9945 feet and making this the highest pass in the Sierras. At the top, newly restored gates welcome you to Yosemite National Park and the alpine meadows along the Tuolumne River. We appreciated the turbo's work on the way up, as it packs the engine with enough oxygen to compensate for the speed-sapping effect of altitude, which reduces a normally aspirated engine's output by three percent for every 1000 feet of elevation. On the way down, we equally appreciated the upgraded brakes, which feature large, 12.6-inch rotors in front and 12.4-inch examples in the rear.
You meet an even greater challenge when you turn off U.S. Highway 395 just beyond Bridgeport into the Sonora Pass on California Highway 108, an old pack trail pushed across from the western slope in 1861. When you pass the U.S. Marine Corps's mountain warfare training center, the road through the tall Jeffrey pines rolls up and down and back and forth like an amusement park ride, and you roar into switchbacks that unexpectedly pitch upward into twelve-percent grades. To keep the Mazdaspeed 6 on the boil, it's best to short-shift the engine, since the thrust diminishes after 5500 rpm. Fortunately, the six-speed gearbox is terrific, and the compact twin-shaft layout promotes clean, low-effort shifts even when it's loaded up with torque.
The 9624-foot crest of Sonora Pass is only twelve miles away from Highway 395, but the road is also great across the western slope another twenty miles, all the way to Strawberry Lake. The Mazdaspeed 6 is generally up to this task, as the Mazda 6's chassis structure has been reinforced to deliver a 50 percent improvement in torsional rigidity: the suspension spring rates are 25 percent stiffer up front and 37 percent higher at the rear, and the antiroll bars are firmed up as well. At the same time, there's no denying that this is a heavy car at 3589 pounds, and 60 percent of that weight is distributed over the front wheels. As a result, you have to drive the Mazdaspeed 6 with a sense of anticipation, as stabbing too late at the brakes and clumsily flicking the steering wheel will make the car feel slow, heavy, and obstinate.