BMW has never bought into the traditional, truck-based SUV.

Instead the company has built car-based crossover-style SUVs, which it calls sports activity vehicles, since it introduced the X5 for the 2000 model year. Welcome the X6.

Searching for a new market niche, BMW cut down the X5’s wagon body to create a coupelike roofline and released it as the X6 last year. BMW calls it the world’s first sports activity coupe. I call it a high-riding, four-passenger, four-door hatchback with an in-your-face attitude and looks that dare to be different.

For 2010, BMW is turning the attitude up to a new level by adding the X6 M model. The X6 M and its X5 M sister are the first BMW X (i.e. crossover) models to get the high-performance M treatment, which includes a powerful engine, chassis tweaks to make it racetrack ready and sporty interior touches.

On the outside, the X6 M announces its presence with authority thanks to standard 20-inch tires, side “gills” behind the front wheels, a more angular front fascia with large air intakes and a rear diffuser that surrounds quad exhaust outlets.

Powering the X6 M is a version of the 4.4-liter twin-turbocharged V-8 engine used in the X6 xDrive50i model. The M engine has its own pistons, camshafts, cooling system and a unique exhaust manifold that pairs the exhaust gas from opposite sides of the engine’s firing order and sends it to the dual turbochargers.

Capturing exhaust in this manner produces a more consistent stream of air that both aids power and reduces turbo lag. The stats are impressive: a whopping 555 horsepower, 500 pound-feet of torque and a 0-60-mph time of just 4.5 seconds.

Underneath the X6 M’s suspension uses the same geometry as base models, but it gets its firmer bushings, springs and suspension links, and a 10-mm lower ride height. A rear air suspension is standard, as are all-wheel-drive and BMW’s adaptive drive. Adaptive drive comes with adjustable shock absorbers and active roll stabilization, which twists the anti-roll bars to firm them up and thus prevent the vehicle from leaning in turns. The brakes are larger as well, with vented rotors measuring 15.6 inches up front and 15.2 inches in the rear.

Inside, the X6 M has sport bucket seats, a thick M sport steering wheel, unique gauges with a programmable rev limiter and a mysterious M drive button on the steering wheel. Programmed through the standard iDrive control system, the M button is a one-touch way to firm up the suspension, leave more room for play in the stability control system, increase throttle response, hold gears longer and add a rev counter warning in the optional head-up display.

I had the opportunity to drive the X6 M on Georgia’s Road Atlanta 2.5-mile road course in Braselton, and I can say that it is a true performance vehicle worthy of the M badge. The engine is astounding. A stab of the throttle provides a rush of acceleration without the slightest hint of turbo lag. Power is prodigious at all speeds. The only problem is fuel economy, which is predictably low at 12 mpg city and 17 mpg highway.

All that power is pushed through a responsive six-speed automatic transmission. Drivers can shift manually via a pair of standard aluminum steering wheel shift paddles or the gearshift. Nudge the gearshift into the sport mode and the transmission holds gears longer to provide more willing power.

In S mode, I found the transmission was in the right gear 95 percent of the time during racetrack driving.

On the track, the X6 M handles better than it should for its size and weight, thanks to quick, responsive steering and a stiff suspension. The standard xDrive all-wheel-drive system comes with dynamic performance control, which can multiply torque to the outside rear wheel to help steer the vehicle through a turn. It’s hard to feel the system operate, but I swear I could feel it pulling the vehicle through a corner on Road Atlanta.

Track driving also revealed that the X6 M corners flatter than any SUV. However, due to its high center of gravity and considerable mass, the X6 M isn’t as flat or as nimble in quick changes of direction as a sport sedan. Despite that mass, the large brakes offer confident stopping power, which was pretty darn important at speeds topping 140 mph.

All that performance talk is fine, but what is it like to live with the X6 M? Well, the stiff suspension settings and short sidewalls can take their toll on passenger comfort. Even with the adjustable shocks in the comfort setting, the X6 M reacts harshly to sharp bumps and the ride is stiffer than many drivers would prefer for everyday use. Given Chicago’s pockmarked streets, I’d recommend driving the X6 M before you buy to make sure you can live with the ride.

Like other X6 models, the M has some useful cargo and passenger space, but not nearly as much as a typical crossover SUV. It holds only four passengers, which might turn off some families, and rear head room is tight. Cargo space maxes out at 59.7 cubic-feet with the rear seats folded down.

In the final analysis, there are certainly many more practical ways to spend $89,725 for a vehicle to haul around the family or impress clients. But there aren’t many more fun ways. Sometimes, it’s fun to crack an egg with a hammer.

2010 BMW X6 M

ENGINE: 555-horsepower 4.4-liter twinturbocharged V-8

TRANSMISSION: six-speed automatic

DRIVETRAIN: all-wheel drive

FUEL ECONOMY: 12 city/17 highway

AS TESTED: $89,725

WEB SITE: BMWusa.com