Most automobiles are using more aluminum parts all the time. Aluminum is light, and in most cases, light is good, as long as it's also strong. Many luxury sedans have a couple of aluminum fenders or an aluminum hood; a few have complete aluminum bodies. The XJ, on the other hand, is made almost entirely of aluminum from the chassis crossmembers up. It has a conventional unit-body design, meaning the body and chassis are a single, assembled piece, with some visible elements of the exterior serving as structural, load-bearing components. But the XJ's unit-body is entirely aluminum, with steel subframes that cradle the engine and suspension.

The XJ L and other long wheelbase models are the longest cars in this class. They're a fraction of inch longer than the Mercedes Benz S-Class, and 1.4 inches longer than the longest BMW 7 Series. Yet the XJs are also the lightest, thanks to their aluminum intensive construction. Other things equal, lighter means better performance and better fuel economy.

Of course, no one will be thinking about the aluminum when they're sizing-up the XJ in a showroom. We suspect many buyers choose Jaguars for the styling, and there's no mistaking this big sedan for anything other than a Jaguar. The XJ looks as though it's ready to pounce even when it's standing still.

The hood has the traditional curves that flow back from the top edges of four round headlights. The wide grille protrudes forward slightly and the leaping jaguar, called the Bonnet Leaper, sits on top of the hood. The rear is uncluttered and features iconic triangular taillight clusters.

From the side, the XJ has a high belt line, the trend at least partly because people feel safer with taller side panels. This makes the side windows appear shallower. The windshield is set at a modern, raked angle. The subtle way in which the belt line edges up as it runs toward the rear gives the car a purposefully crouched look. All the glass is laminated, with two layers separated by an ultra-thin acoustic interlayer, which cuts interior noise and protects trim from the damaging effect of UV radiation. Jaguar also claims that the laminated side glass makes smash-and-grab thefts more difficult.

All XJs now feature the wire-mesh grille introduced on the high-performance XJR, though the R model still sports a unique body-color grille surround and other design tweaks that give it a more aggressive look. These include thin-spoke, 19-inch wheels.

Wheel packages range from 18 to 20 inches in diameter. For appearances sake, we generally say bigger is better, and that applies with the XJ. On the other hand, larger wheels (and therefore shorter tire sidewalls) tend to produce a slight decrease in ride quality, or at least more tire noise.