A8 L models are 5.1 inches longer than the standard A8 and S8. (L stands for long-wheelbase.) Inside the car, those 5.1 inches translate entirely into increased rear-seat legroom. Choose the A8 over the A8 L if squeezing into tight parking spots is more important than a vast rear seating area, remembering that the standard A8's rear accommodations are quite expansive by typical sedan standards.

At 115.9 inches, the standard A8 is fractionally longer in wheelbase than a Cadillac DTS. The A8 L is essentially the same length overall as a Mercedes S-Class and BMW 750i. The A8 L wheelbase stretches 121.0 inches, which leaves it 3.6 inches short of the long-wheelbase Mercedes and 2.2 inches short of the long-wheelbase BMW. Other things being equal, a longer wheelbase offers more passenger room and increased stability at speed, but is less maneuverable on canyon roads and in tight parking lots. The Audi is an inch wider than the Mercedes-Benz and comparable to the BMW.

All the doors open extra wide, making it easy to get in and out. The flush, lever-style outside handles are attractive, but we find them harder to use than the type you can put your hand through, such as those on a Mercedes.

Standard on A8 4.2s are 10-spoke 18-inch alloy wheels with 255/45HR18 all-season tires; these provide excellent handling and ride comfort and superb grip in the wet. The optional 19- and 20-inch wheels and tires more aggressively fill the wheelwells and provide a surprisingly smooth ride in spite of their short sidewalls. The A8 L W12 gets the 19-inch wheel/tire package standard; with 20-inch wheels available and 18-inchers (which offer the best ride) offered as a no-cost option.

All models feature a tall, vertical grille that connects Audi's familiar horizontally split grilles over the front bumper, emphasized with a chrome surround.

The rear of the A8 models feature taillights that fit flush with the clean rear design. Turn signals use LED technology and feature side repeater lamps to signal your intentions to drivers alongside. Dual exhausts poke from below the beautifully integrated rear bumper.

The S8 has a bolder front end, with a bright finish emphasizing the vertical elements of the family grille, and a honeycomb texture for the air intakes on either side of it. A red-and-black S8 badge is offset to the lower right. Sharp-eyed Audi-watchers might notice additional S8 badges on the front fenders and front brake calipers, as well as a V10 badge on each front fender and unique aluminum-look trim on the side mirrors and door handles. Subtle, too, are the S8's integrated deck-lid spoiler and light-reflecting panel in its rear apron; not so subtle are its four oval exhaust tips.

The aluminum space frame saves about 300 pounds compared to a conventional steel frame, allowing more features without overburdening the car with weight. An A8 L 4.2 weighs 150 pounds less than a BMW 750Li and only 23 pounds more than a Mercedes-Benz S550, neither of which have all-wheel drive. The A8 benefits from a highly rigid structure, which means less flex, and the A8 feels as if it's milled from a single block of bar-stock aluminum. A rigid structure is the key to a smooth ride quality and sharp handling.