A road trip is always the perfect way to test a car.

In this case, the destination was Detroit and the North American International Auto Show. So, it was time to pack up and head west with a fellow troublemaker.

While our destination was a cold, rather gritty city, our method of transport, the Audi A6, was, by contrast, a smooth, easy ride.

The A6 is available as a sedan and as a wagon called the Avant. Both are available in front-wheel-drive or with Audi's all-wheel- drive Quattro system. Three engine choices are available: The top-of- the-line 4.2-liter, 300-horsepower V-8; the mid-level, 2.7-liter, turbocharged V-6 with 250 horsepower, and the all-new base 3-liter, 220 horsepower V-6. It replaces the old 2.8-liter V-6.

Audi provided the 3-liter V-6 model for testing, because it is the only model with the continuously variable transmission with Tiptronic.

A continuously variable transmission is an automatic transmission without any gears. You never feel a shift between first and second gear because there is no first or second gear, only a drive gear. The power builds without any lurching. Similarly, there's no downshift with a kick of speed and when you lift off the accelerator, the car slows down without a feel of shifting.

This seamlessly smooth drivetrain, according to Audi, is faster than a five-speed manual and more fuel efficient. Indeed, despite a highway rating of 25 mpg, the test car yielded more than 28 mpg, with some stretches yielding close to 30 mpg. That's excellent for a luxury sedan.

Until now, getting a steel belt that could handle the torque was the reason the continuously variable transmission has been used only on small economy cars. Audi has resolved this problem resulting in an excellent drivetrain.

The car never lacks for power. No matter how much or how little pressure is applied to the accelerator, the car responds appropriately. It never feels underpowered, with Audi claiming a 0- 60 time of 7.1 seconds.

Also unusual is that the revs stay constant when driving at a certain speed -- say 65 mph -- and encountering a hill and needing more power.

Strangely, Audi provides a Tiptronic mode for this car, allowing the driver to manually shift through six traditional "gears" with the help of microchips. It feels unnatural and isn't very necessary.

The rest of the car is standard Audi A6.

Electronic Stability Program with Brake Assist ensures that the driver stays on the road in emergency situations. Traction control and anti-lock brakes also are standard. So are side impact airbags.

Handling is nearly perfect.

The suspension provides just enough road feel to telegraph to the driver what's going on. Road shocks are well-absorbed. In Detroit, where the streets are one long pothole, the Audi A6 was able to take a beating and keep on going. There wasn't any body lean or jounce and ride motion was well-controlled.

The speed-sensitive steering was perfectly weighted and quick when needed. Braking was short and quick.

The tree-lined hills along Interstate-80 in Pennsylvania gave way to the unrelenting flatness of Ohio, with boring cities like Akron, Youngstown and Toledo. The state has some of the cleanest rest stops I've ever seen and some of the meanest state troopers. While one would love to drive through as quickly as possible, the troopers make that impossible.

That's what made traveling in the A6 so nice. The cabin is stocked with the luxury accoutrements expected of the class.

Gauges are complete, including a speedometer, tachometer, oil temperature, water temperature and voltage. A multi-function trip computer is always handy and resides between the speedometer and tachometer.

The dual-zone climate control has a sensor that automatically shuts off inductio of outside air, when air pollution is too high.

The AM/FM/cassette/CD audio system had a convenient in-dash 6-CD changer and superior sound. It belted out R&B greats like Ruth Brown with crystal clarity.

The tilt-telescopic steering wheel and power front bucket seats with articulating headrests made the trip extremely comfortable. The seats are supportive in all respects. Seat heaters, both front and rear are available for $550 and feature multiple temperature settings. They helped warm the leather seats quickly. The wood trim on the dash and door panels gave the interior an elegant appearance.

The headlamps are operated manually, in contrast to those on most luxury cars. Ditto the lack of an auto-dimming rearview mirror, automatic door locks and memory seats. I loved the lack of a navigation system. More important were the map pockets, perfect for holding the old-fashioned way of navigating.

But they weren't missed. These gimmicks aren't necessary when the task at hand is driving. Driving pleasure is the luxury here.

Still, I appreciated the Preferred Luxury Package, consisting of the leather trim and a glass sunroof, at $1,800. A Premium Package, consisting of steering-wheel mounted audio controls, Xenon high intensity discharge headlamps and rear parking sensors, was $1,200. I even appreciated the trunk trimmed with a cargo net to help keep packages from moving around at speed.

Bottom line was $39,535 for perhaps one of the finest luxury sedans I've driven.

That does come with a caveat. Midway through Ohio, the "check engine" light came on. There was no loss in performance, nor was there anything wrong with the car. So, we motored on without a problem. It wouldn't prevent me from recommending the car, and its fast, but fuel-conscious drivetrain, to anyone looking for one of the finest luxury cars available today.

It's even nice enough to enhance a trip to Detroit.

AUDI A6 3.0 CVT

Engine: 3-liter DOHC V6

Transmission: Multitronic continuously variable automatic

Tires: P205/55R16

Wheelbase: 108.7 inches

Length: 192 inches

Width: 71.3 inches

Cargo volume: 17.2 cubic feet

Base price: $35,400

As tested: $39,525

EPA rating: 19 city, 25 highway

Test mileage: 28.3

Fuel type: Regular

Built in: Neckarsulm, Germany