It's light -- but no lightweight

By DAN NEIL

Oct. 22, 2003 12 AM PT

With all the shrillness at their command, SUV zealots seized upon last week’s report by the federal government that correlated lower vehicle weight in passenger cars with higher fatality rates. One conservative lobbying group, the Competitive Enterprise Institute, gloated that the report showed that fuel economy standards were “even deadlier than previously thought.”

The study indicates no such thing, and the institute’s spin on the topic is the stuff of magic mushrooms. It does say that drivers of lighter vehicles have tended to come out on the short end of the stick, mortality-wise, in collisions with heavier vehicles. As the owner of a small vintage sports car, I do not take this conclusion, um, lightly.

At issue here is the relationship between crashworthiness and fuel economy. Given that the Bush administration plans to revise mileage standards for light trucks -- meaning sport utility vehicles, pickups and minivans -- a key question is: Would a drive toward lighter and more fuel-efficient vehicles cost lives? The answer: not necessarily.

Smarter design can compensate for a lighter vehicle’s loss of Newtonian leverage.

Consider the Jaguar XJ8. For model year 2004, the venerable dame of British sedans has been reincarnated as a high-tech showpiece, its most salient feature being its all-aluminum, lightweight construction. The chassis is an aluminum monocoque, an assembly of alloy panels, beams, castings and extrusions that are riveted and glued together rather than welded like a steel unibody. Rival Audi’s A8 L is an aluminum chassis car also, but the construction technique found in the XJ8 is more like that used in the Aston Martin Vanquish, the Lotus Elise and the Panoz Esperante (if the last two seem obscure, it only goes to show how exotic this method is).

The result is that the new XJ8 -- which is bigger, faster, more powerful and more richly appointed than its predecessor -- is also 200 pounds lighter than its forerunner and quite a bit lighter than many of its competitors. The aluminum diet helps the XJ8, with a 4.2-liter, 294-horsepower V-8, return the highest Environmental Protection Agency-rated gas mileage of any luxury sedan, a conscience-clearing 28 miles per gallon highway and a combined rating of 22 mpg. That’s a full 10% higher than the previous model.

Oh, and by the way, it romps to 60 mph in 6.3 seconds (half a second faster than before), carries four sets of golf clubs in the trunk and seats five people in a vibe of deep civility and leather-bound cool.

But is it any less safe for being lighter? I don’t think so.

The government study, issued by the National Highway Traffic Safety Administration, is judicious on the matter of vehicle weight and safety, pointing out that although the conservation of momentum favors occupants in heavier cars, mass alone does not make a vehicle safer. Under the heading “crashworthiness,” the study says that heavier cars, “with their longer hoods and extra space in the occupant compartment provide an opportunity for a more gradual deceleration of the vehicle, and the occupant within the vehicle” in a collision.

What if you could build a big car that also was lighter? The report goes on to say: “While it is conceivable that light vehicles could be built with similarly long hoods and mild deceleration pulses, it would probably require major changes in materials and design.”

The aluminum Jaguar XJ8 embodies such changes. This car is 200.4 inches long -- nearly 17 feet -- and the revised design retains the pip-pip classicism of the older XJs, with the long, graceful hood swept back in fluted contours from the quad headlights. Under the hood, Jaguar has engineered a bolt-on front structure that can sustain impacts of up to 10 mph without deforming the remaining structure, which is itself protected by extruded aluminum “crush tubes,” sacrificial members that deflect crash energy away from the cabin. The 2004 XJ8 has not yet been crash-rated by NHTSA or the Insurance Institute for Highway Safety, but I’d be very surprised if it doesn’t get full marks in crash protection.

Another factor that has historically favored heavier vehicles in collisions is structural integrity. The beefier steel members in heavy cars, around doors and along roof rails, can fend off impacts from other vehicles. However, the Jaguar’s aluminum structure -- 60% stiffer, or more rigid, than the steel-bodied car it replaces -- seems to suggest that the choice between weight and safety is a false one. The cabin openings are ringed with high-strength alloy extrusions, and similar structures gird the floor, roof and bumpers. It all looks as if it can take a pretty good lick.

NHTSA’s study also notes that bigger cars, not necessarily heavier cars, are more dynamically stable. Longer-wheelbase cars have less of a tendency to spin; wider vehicles have less of a tendency to roll over. The Jag’s wheelbase is 119.4 inches, 5% longer than before. And yet it’s 5% lighter. Go figure.

As for the relationship between size and directional stability, the current generation of driver-assist technologies -- including stability control, which was not widely available during the 1991-99 period covered by the NHTSA study, can largely compensate for smaller cars’ friskier dynamics.

The XJ8 offers a full suite of driver-assist systems, including anti-lock and stability control, traction control, emergency brake assist, adaptive cruise control (it maintains a set distance from the vehicle ahead), as well as air suspension and semi-active dampers.

Which brings us to the last explanation the report offers as to why heavier cars have been historically safer: Heavier cars were more expensive cars, in which early iterations of equipment such as air bags and anti-lock brakes were available. These days, however, some of the lightest cars, such as an Acura RSX, have a full complement of such systems.

For the record, the XJ8’s air bags (front, side and window curtain) are controlled by something called the Advanced Restraint Technology System. The sensors keep tabs on the occupants, accounting for their position and weight as well as the type and severity of impact -- factors crucial to the millisecond timing of air bags.

The 339-page NHTSA study is a worthy contribution to the debate on vehicle safety. But it does not support the conclusion that tougher mileage standards would inevitably lead to more death on the highway. Anyone who says so is pursuing an agenda quite apart from safety -- and is hoping you won’t read the report yourself (available at www.nhtsa.gov).

Frankly, I didn’t expect the new XJ8 to be an avatar in the safety and fuel-mileage debate, but there you are. I have always regarded this model to be the most beautiful and ineffably stately of large sedans (excepting that period in the late 1980s and early 1990s when Jaguar chose to iron the curves out of the bodywork and use headlights that looked like Halls cough drops). It remains so in this generation.

The trick for Jaguar design chief Ian Callum was to retain the iconic styling of the car yet give it a firmer visual foundation (stretch the wheelbase relative to the body) and enlarge the cabin. Previous XJs, with their long, shallow greenhouses, were pretty cramped for luxury cars. The new XJ8 remains intimate yet offers much more elbow room and headroom. It’s a very comfortable car.

There are three models available. In addition to the base XJ8, which I drove, there is the Vanden Plas, which offers more limousine-like appointments such as deep-pile lamb’s wool rugs, an electric rear sun blind and a premium sound system. The performance-tuned XJR uses a supercharged version of the engine (390 horsepower), a racier suspension setup (lowered ride height, stiffer air springs, 19- or 20-inch high-performance Z-rated tires and the bigger Brembo disc brakes).

I opted to test the base XJ8 because, among other things, it is a good value: $59,995 base price (the Vanden Plas starts at $68,995 and the XJR, $74,995). The cabin certainly doesn’t look or feel value-driven. Broad panels of burled walnut grace the dash, doors and central console, and the interior is brightened with chrome bits around the gearshift. The visual center of gravity is a large liquid crystal display used for both the navigation and audio functions. It works well enough, though these touch-screen units are easily smudged with fingerprints.

I often wonder what kind of car I myself would like to own as a daily driver. The XJ8 has some sporting guts, and it’s plenty quick enough to dispatch ornery commuting traffic. But it’s best at cruising altitude, because the car is lazy off the mark till the revs pick up. The car’s air suspension is cloud-like, and interior ambience is lushly quiet, a kind of alpha-wave bell tone. I’d like to drive this thing to, say, Alaska.

Key to the car’s appeal -- and its fuel mileage -- is the new ZF six-speed transmission, a unit found in several of the Jag’s competitors. No matter. It works beautifully, and at highway speeds it drops into its very tall sixth gear, allowing the engine to turn lazily and save fuel.

Maybe gas mileage doesn’t matter to you. The Jag XJ8’s lack of vices recommends itself, then, in spite of the car’s virtues.

Times automotive critic Dan Neil can be reached at dan.neil@latimes.com

2004 Jaguar XJ8

Wheelbase: 119.4 inches

Length: 200.4 inches

Curb weight: 3,803 pounds

Powertrain: 4.2-liter, double- overhead-cam, 32-valve V-8 engine; six-speed automatic transmission; rear-wheel drive

Horsepower: 294 at 6,000 rpm

Torque: 303 pound-feet at 4,100 rpm

Acceleration: zero to 60 mph in 6.3 seconds

EPA rating: 18 mpg city, 28 mpg highway, 22 mpg combined

Price, base: $59,995, includes destination charge ($665)