Road Test: 2008 BMW X6 xDrive50i
By Shaun Bailey of Road & Track
Laurens, South Carolina — The BMW X6 xDrive50i is a behemoth, but in BMW fashion it tosses sport-ute convention out the window in favor of sports-sedan flair. It tips the scales at a whopping 5270 lb., has 8.3 in. of ground clearance, seats only four and has limited rear storage space due to its coupelike roofline. Thankfully, the X6 has plenty of character and makes up for some of its impracticality by being quick and nimble.
First time I looked at the X6, I saw an X5 with reduced functionality. It is, after all, built on the same platform and assembly line in Spartanburg, South Carolina. Being a slave to style resulted in the loss of the center rear seat and about half the storage space. Still, rear-seat head room is ample at 36.0 in. That's a full inch more than in the 335i sedan and equal to that of 5 Series' models; it lacks only that center rear seat of those smaller sedans.
Like most Road & Track readers, I prefer cars that follow Colin Chapman's philosophy of lightweight car design. The X6 does not, yet in its own way it stirs the enthusiast soul. I can envision the broad-shouldered X6 bombing across open desert, pounding over rough roads and traversing snowy-mountain passes. But it's illusory, as the X6 has roll-rates like a track car and rides on 20-in. wheels shod with sticky rubber meant for pavement. Our test car had the optional sport package that includes the larger wheels, summer performance run-flat tires, active shock valving and staggered wheel widths. If you think these alloys look small, 21s are available, while base models wear somewhat diminutive 19s. Cars for the U.S. will have a useful full-size spare wheel and tire, even when equipped with run-flats.
What separates the X6 from others of its ilk is that it really backs up the claim to be what BMW likes to call a Sport Activity Vehicle, with performance numbers well beyond the realm of reasonable for ordinary SUVs. Looking at the data, you can see that the X6 matches up with the much-lauded 335i. Only in the slalom does the X6 suffer, but this has to do with a low-level stability-control system that cannot be disabled and is designed to inhibit rollover that might occur during fast transitions — like those in our slalom. All BMW X-family vehicles are so equipped. The system was never invoked anywhere else during our test.
The X6 is going against the laws of physics, but that didn't stop the engineers at BMW from trying to turn a 2.5-ton SUV into a true sporting machine. They did it with a host of technology that has been brewing on other BMWs for the past few years, and the addition of some new ones. The latest technology is the Dynamic Performance Control system that can transfer torque left to right at the rear differential. This combines with the xDrive all-wheel-drive system that already shifts torque front to rear. All this is, of course, controlled by computers that sense the car's yaw rates, steering input, lateral acceleration and throttle. With that information, the computers predict where the driver wants to go and make the car go there. What's unique is that DPC can be used to control small understeer/oversteer conditions without the intervention of stability control. It does this with a complicated set of clutches and planetary gearsets around the rear open differential. When cornering, DPC can transfer torque to the outside rear wheel to help rotate the car and decrease understeer. For entertainment's sake, a display on the dash shows power flow to each wheel. Punch the throttle, and each rear tire's power bar grows accordingly. The pure functionality of DPC makes the system's additional 26.5 lb. worth its weight. Surely we'll see this technology on something a little lighter, the M3 perhaps, although an engineer pointed out that the system provides the biggest performance gain on awd vehicles to aid in decreasing understeer.
Our car had the added benefit of Electronic Damper Control and Active Steering. Both systems operate with the Adaptive Drive system that controls roll with electronically adjustable anti-roll bars, both front and rear. It's a lot of techno wizardry that makes the X6 work so well — and it's almost completely transparent to the driver. I can't help comparing it to a modern fighter jet that is so unstable that a computer is required to keep it flying straight. The X6 goes straight just fine, but throw it into a corner and a bunch of computers finesse the car's attitude to make sure you hit your apex. The result is a truly precise and dynamic ride that doesn't fail to impress. Its performance abilities really come out in the wet and if you can't tell from the photos, it rained a lot during our test drive in South Carolina. The X6 is incredibly stable while not suffering from the heavy understeer we would have predicted. On hard driving around the track it picks up mild understeer like a 3 Series sedan. Backing off the throttle and trail-braking aggressively into a corner will induce controllable oversteer, but it gathers itself back up in a hurry. Its characteristics are not unlike the new Nissan GT-R, Mitsubishi Lancer Evolution or Subaru WRX STI. The limits just aren't as high as those machines, but what do you expect of a 2.5-ton beast with 8.3 in. of ground clearance?
The heart of the X6 is a 4.4-liter twin-turbocharged V-8 that pumps out 400 horsepower and 450 lb.-ft. of torque. The engine's heads are reversed compared to more conventional layouts, allowing the two small turbos to nestle like a supercharger in the valley of the V-8's block. Intakes are on the outside of the engine and the exhaust runs down the back out around the transmission. Open the hood and there's nothing to see other than a plastic cover, but open the throttle and there's plenty to hear. At first crank the engine throbs to life at 1400 rpm. It eventually settles down to a 700-rpm rumble that lets you and your neighbors know it's not a family car. The turbochargers naturally muffle the exhaust and at full tilt the X6 isn't a screamer. Instead it emits a bulk-appropriate guttural snarl.
Flying laps around a test track quickly demonstrate how adept the X6 is on pavement. Pushing 110 mph down a short straight is easy. Braking hard for a medium right-hander while thumbing the paddles to manually downshift the 6-speed automatic elicits quick rev-matching blips that can't be felt — only heard. Back off the brakes and turn the heavy, yet communicative wheel slightly and the X6 stays flat with only a mild and easily controllable push. Back off the brakes more and there's enough rotation without steering input to get back on the throttle, whereby the X6 squirts out of the corner. Yes, the 2.5-ton X6 squirts out of corners and makes you wonder where the weight went.
BMW also offers the X6 with the twin-turbo inline-6 from the 335i and 135i that makes 300 bhp. It's aptly named the X6 xDrive35i, and is distinguished by its dual round exhaust tips, smaller brakes and fake front corner air inlets. It also manages to shave 375 lb., but it's not nearly as quick.
I applaud BMW's ability to overcome obstacles and engineer a truly sporting SUV that still has a useful tow rating of 3500 lb. While there is little, if any, competition to rival the BMW for on-road comfort and refinement, in a time of high gas prices, I don't know if the X6 xDrive50i is the answer to some unmet need. It might be too much about flaunting massive on-road excess, rather than off-road prowess.