Porsche is changing. The company known for rock-solid sports cars started its transformation earlier this decade by developing the Cayenne, an SUV that is sporty both on road and off. For 2010, Porsche adds its first-ever sport sedan and expands its lineup to four models, two more than it had in 2000.

The 2010 Porsche Panamera is a grand-touring luxury performance sedan aimed at the likes of the Audi A8, BMW M5 and 7 Series, Maserati Quattroporte and Mercedes-Benz S Class. Unlike any of those cars, the Panamera uses a hatchback body design – a logical choice given the company’s requirements that the car have a spacious rear seat and plenty of cargo capacity.

The 2010 Panamera is offered in S, 4S and Turbo models, the S with rear-wheel drive and the others with all-wheel drive.

The S ($89,800) and 4S ($93,800) feature a 400-horsepower 4.8-liter V-8, while the Turbo ($132,600) gets a 500-horsepower twin-turbocharged version of the same engine. Both engines are mated to Porsche’s Porsche Doppelkupplung (PDK) seven-speed automated manual transmission. The PDK uses two clutches, one to hold the current gear and one to ready the next so power to the wheels is never interrupted.

The best-equipped Porsche ever, the Panamera S and 4S models come standard with equipment such as leather upholstery, quad bucket seats, a navigation system and a sunroof. The high-luxury Turbo gets adaptive air suspension, adaptive headlights and full leather upholstery and interior trim.

Options are numerous and they can add up to $60,000 to the price of the car. They range from performance features such as anti-roll control and Porsche’s Sport Chrono Plus stopwatch with launch control to interior amenities like high-end Bose and Burmester audio systems and the option to trim numerous interior bits in leather, Alcantara, wood or aluminum.

Not that the base interior really needs extra trim. The fit and finish and quality materials rival anything from the competition. It does have a complicated set of buttons, with up to 32 on the center console that juts out from the dash, another 18 on the center of the dashboard and still other functions controlled through the navigation system’s touch screen.

Like other Porsches, the Panamera’s instrument cluster features the tachometer front and center.

This is a driver’s car, after all. The speedometer, with its hard-to-read 25 mph increments, is set to the left and a multifunction display sits opposite it to the right. This display teams with the navigation screen to allow drivers to view all types of information in two places.

The feel from the driver’s seat is much like that of the 911, only higher off the ground. Thanks to supportive seats and plenty of head and legroom, all passengers will be comfortable. The interior’s full-length center console splits the rear seat in two, eliminating a center position but making for plenty of shoulder room.

The hatchback area makes it useful as a family vehicle, too. With the rear seats up, there is 15.6 cubic feet of storage space in back, about as much room as in a midsize sedan’s trunk. Capacity expands to 44.2 cubic feet with the rear seats folded down, which is as much as a Subaru Impreza hatchback.

While the Panamera’s room and luxury are impressive, it drives even better. The Panamera offers the performance of a world-class sport sedan with the comfortable ride and refinement of a luxury cruiser. A lot of engineering went into the car to make those extremes possible. The Panamera also comes with two forms of adjustable suspension that turn the ride from soft but stable to racetrack ready.

The base suspension’s comfort mode isn’t too soft and the sport setting isn’t too firm. The Turbo’s adaptive air suspension adds a firmer sport plus mode. It can also lower the car 1 inch for better handling and stability and raise it 0.78 inch to help the front end clear curbs. Also offered is Porsche dynamic chassis control, which firms up the anti-roll bars to counteract body lean in turns and disconnects them to improve straight-line comfort on bumpy roads.

I had the opportunity to drive the Panamera on the 4.1-mile Road America course in Elkhart Lake, Wis. On the track, the Panamera’s quick, precise steering stood out. It dove readily into turns and remained flat. The PDK, set to sport plus, had the right gear for best power delivery 99 percent of the time, eliminating the need to use the shift paddles. The brakes, however, did fade and the rotors warped in the frighteningly fast Turbo model.

Don’t worry, though. The base brakes will do just fine on the street. If you really want to take your Panamera to the track, invest in the $8,860 composite ceramic brakes.

All Panameras are fast. The base V-8 in S and 4S models delivers as much power as anyone would need, launching the car from 0-60 mph in as little as 4.6 seconds. The Turbo cuts that time to 3.8 seconds, with little if any turbo lag and a rush of power that pins you back in your seat.

For all that power, the Panamera goes relatively easy on gas. It comes with a start/stop feature that turns the engine off at stoplights to conserve fuel.

Environmental Protection Agency fuel economy estimates are a reasonable 16 mpg city/24 mpg highway for the S models and 15/23 mpg for the Turbo. They’re so reasonable that no Panamera is saddled with a gas guzzler tax.

Bottom line, the 2010 Porsche Panamera is a great way to expand the Porsche lineup. It performs well on the street and the track and offers enough passenger and cargo room to make it a useful family car.

Put simply, the Panamera enters the market as one of the world’s best luxury sport sedans.

2010 PORSCHE PANAMERA

ENGINES: 400-horsepower 4.8-liter V-8 (S and 4S), 500-horsepower twin-turbocharged 4.8-liter V-8 (Turbo)

TRANSMISION: seven-speed automated manual

DRIVETRAINS: rear-wheel drive (S), all-wheel drive (4S and Turbo)

FUEL ECONOMY: 16 mpg city/24 mpg highway (S and 4S), 15/23 (Turbo)

BASE PRICES: $89,800 (S), $93,800 (4S), $132,600 (Turbo)

WEB SITE: Porsche.com