The Good: Serious speed, roomy interior, optional adaptive damping system

The Bad: High price, mediocre fuel economy, no third-row seats

The Bottom Line: Porsche-style speed with Mercedes luxury and convenience


The new 2008 ML550's new 5.5 liter V8 engine, great looks and lithe performance explain why this big SUV is still a big seller

Up Front

One of the oddities of the car market is how well big SUVs are selling, despite the rise in gasoline prices. And among the hottest right now is one of the most expensive: the Mercedes-Benz M-Class. Last year, U.S. sales of the M-Class rose 7.1% to 33,879—and then soared 37.7% to 3,237 in January.

Why is the M-Class selling so well? It certainly isn't because of its low price. The entry-level ML350 starts out at a hefty $44,825, rising to $53,575 for the speedier ML550. The price tops out at $87,825 for the superspeedy ML63 AMG. Add options, and the price soars.

The M-Class' fuel economy isn't great. The diesel-powered ML320 CDI gets decent gas mileage for an SUV: It's rated at 18 mpg in the city and 24 on the highway. But it drops to 15/20 mpg for the gasoline-powered ML350. The ML550 does as well as the ML500, the less-powerful model it's replacing, but it still is only rated to get 13 mpg in the city and 18 on the highway. The AMG version, needless to say, does even worse (11 city/14 highway).

After a week spent test-driving the 2008 ML550, I think I get it: The people who buy higher-end Mercedes aren't on tight budgets. And if penny-pinching isn't a great concern, a Mercedes SUV is tremendously appealing.

Introduced a decade ago, the M-Class is a tall, old-style SUV, the kind where you have to reach down to use an ATM. It combines a comfortable car-like drive with an armored-truck-like feeling of safety, and it has a roomy, well-designed interior that's crammed with convenience features. It's also made in the U.S.A.—specifically, in Tuscaloosa, Ala.

The newest version of the M-Class, the '08 ML550, has a powerful 5.5-liter V8 engine that makes it genuinely fast. The new engine delivers 382 horsepower, 80 more than the 5.0-liter engine in the ML500. By comparison, the V6 engine in the '08 ML350 is only rated at 268 horsepower. That's adequate, but hardly exciting when it comes to accelerating a vehicle that weighs a hefty 4,800 pounds. All versions of the M-Class come with full-time four-wheel drive and an innovative seven-speed automatic transmission.

Both the National Highway Traffic Safety Administration and the Insurance Institute for Highway Safety have awarded the M-Class top crash-test ratings. That's not surprising, considering that the M-Class is packed with air bags and has a steel-reinforced frame with both front and rear crumple zones to protect occupants in serious accidents. Stability and traction control, a roll-over sensor, oversized antilock disk brakes with braking assist, seatbelt pretensioners, and active head restraints are all standard.

The M-Class has one big negative, however: It seats only a maximum of five people, while the BMW's (BMWG) X5, Volkswagen's (VLKAY) Audi Q7, and Honda's (HMC) Acura MDX all can seat up to seven. If you want a Mercedes SUV with three rows of seats, consider moving up to the larger, even more expensive GL-Class.

The M-Class, nonetheless, is a major reason Mercedes' U.S. sales have risen for 14 consecutive years. Its main rivals are also doing very well in the U.S. right now. The BMW X5 saw its U.S. sales soar 31.4% last year, to 35,202, while sales of the MDX rose 7.9% in 2007, to 58,606.

But the M-Class is off to a stronger start this year than its rivals. While M-Class sales soared more than one-third in January, sales of the X5 fell 4.7% and the MDX 4.1%.

Behind the Wheel

The ML550 is a luxury SUV on steroids. Mercedes borrowed all sorts of styling cues from the AMG that give it a far more aggressive appearance than the ML350. These include the big running boards on the side, 19-inch spoke wheels, and a chrome grille with a huge Mercedes logo in its center.

The big V8 gives the ML550 serious speed to match its looks. I clocked it at just under six seconds in accelerating from zero to 60 mph; Mercedes puts it at 5.6 seconds. That's more than two seconds faster than the ML320 CDI and the ML350—and only 0.8 seconds slower than the ML63 AMG. The ML550 is noticeably quicker than the V8-powered version of the BMW X5 and much faster than the Acura MDX and base model Porsche Cayenne. (The Porsche Cayenne Turbo, which sells for $93,700, can blast from zero to 60 in 5.3 seconds.)

The ML550 can be had with every imaginable convenience feature, from adaptive headlights that swivel when you turn to an electronic hatchback that raises and lowers at the push of a button. And anytime you get into a jam, some system comes to your aid. For instance, the standard hill braking regularly kicked in on rural back roads to slow the vehicle on steep, icy hills. When I drove too fast through slush puddles, the wipers automatically cleared the windshield.

Another thing that sets the ML550 apart is an optional Adaptive Damping System (ADS) that allows you to change the ride setting at the flick of a switch. It's part of a Premium III package that costs $8,550, which is a lot, but the package also includes a navigation system, Surround Sound, and numerous other add-ons. ADS is well worth having because it allows you to change switch the ML550 from "comfort" to "sport" mode. In comfort mode, the ride is like a traditional luxury SUV's; changing the setting to sport noticeably hardens the suspension and lowers the vehicle by 0.3 inches to improve stability.

The ML550's off-road capabilities are considerable. The air suspension system that comes with ADS lets you raise the vehicle up 3.1 inches, giving the ML550 an enormous 10.5 inches of ground clearance. I parked my test vehicle in a snowdrift up to the running boards and watched it rise, which is really something. I then took it down into a frozen, rutted dirt road in a river bottom. There was no danger of scraping bottom.

Another nifty option is the dual-screen rear-seat entertainment system ($2,670). This allows two kids riding in back each to have a separate video screen. The screens also are built into the backs of the front seats, which frees up space in the ceiling for a sunroof. The one downside of the Mercedes system is that the DVD player is under the right rear seat, which is an inconvenient place for it to be when you have to load a disk.
Buy it or Bag It?

The gasoline-powered ML350 is the best selling of the M-Class SUVs, but to me it's the least attractive model. If fuel economy is a priority, consider the ML320 CDI. Its rating of only 215 hp seems a little feeble, but because it's a diesel it delivers 398 pound-feet of torque—more than the V8 in the ML550. As a result, its acceleration is as good as the gasoline-powered ML350's. And, for an extra $1,000, the ML320 will save you thousands of dollars in fuel costs. Unfortunately, ML320 CDI won't be available in New York, California, or the six other states with the tightest air-quality standards until a super-low-polluting Bluetec version comes out this summer.

If performance is a priority, the ML550 is a terrific SUV, but its average selling price is a considerable $59,353, according to the Power Information Network (PIN). Only the Porsche Cayenne, at $66,501, costs more, according to PIN. By comparison, the BMW X5 goes for an average of $57,414, the Audi Q7 for $55,833, and the Acura MDX for $42,473.

Dollar-for-dollar, the Acura is by far the best buy in the bunch. But if you can afford to splurge on an ML550, you won't be disappointed.


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