The A4's 2.0-liter turbocharged four-cylinder is designed with everyday use in mind. It's not a fire-breathing hot rod like the turbo in a Mitsubishi Evolution, Subaru STi, or Porsche 911. With direct injection and variable exhaust valve lift, the Audi engine starts quickly and at idle has the faintest muffled ticking. Above that it's smoother because the turbocharger is spooled up and generating boost.

As a result, the 2.0T delivers 211 horsepower, 7 more than the Lexus IS 2.5-liter V6 and just slightly less than the 3.0-liter six-cylinders in the Mercedes C300 and BMW 328 (by 17 hp and 19 hp respectively). Yet far more important for the American driver in a 35 mph world is torque, and the A4's 2.0T dishes up 258 lb-ft of it. This diesel-like urge tops all of the aforementioned engines (by 73, 37 and 58 lb-ft respectively). So the A4 is more than capable of keeping up with or passing those other cars. The A4 2.0T can accelerate from 0 to 60 mph in 7 seconds or less.

More impressive is the width of the powerband, that area of engine speed that delivers maximum power. The 2.0 turbo makes big torque from just off idle at 1500 rpm all the way to 4200 rpm. And from 4300-6000 rpm it delivers the 211 horsepower. It will rev to 6700 rpm, but there isn't much point when you've got that much midrange power. None of the competitors has that kind of flexibility and, just to rub their noses in it, the A4 with quattro all-wheel drive betters the EPA fuel-economy ratings for the analogous BMW, Mercedes and Lexus by 1-5 mpg in both the City and Highway cycles. The A4 Avant 2.0T quattro is rated 21/27 mpg City/Highway. In our own mixed driving, which included elevation, rain and snow, it returned better than 25 mpg.

The continuously variable transmission in the front-drive 2.0T has wider ratios than in previous-generation models to improve acceleration and highway economy. In Drive it operates completely automatically. A CVT feels differently from a traditional automatic: Engine speed more closely matches how hard you're pushing the gas pedal rather than how fast the car is going, sort of like how a car with a manual transmission feels when the clutch is slipping (or a '48-63 Dynaflow, if you're old enough to remember Buick's gearless hydraulic transmission). With the lever in S for Sport mode the transmission makes eight steps automatically (to feel like gear changes even though they technically aren't). In Manual mode (+/- on the shift lever or shift paddles), you control those eight steps by moving the shift lever or paddles.

Six-speed manual cars have a precise shifter with good feel and movement. Likewise, the clutch pedal has simple, low-effort operation. A feature called the drive-off assistant keeps the brakes on while you transition your foot from brake to gas pedal, so even novices can manage an uphill start. Because the A4 can get heavy and the engine is only two liters you may need a few revs on for the smoothest takeoffs, a technique you'll learn by the third stop sign.

The six-speed automatic disengages when the car is in Drive but a foot is on the brake, to save fuel, wear, and the creep motion idling automatics want to do. The six-speed auto offers the same modes (D, S, and manual) as the CVT. In D it is smooth yet shifts quickly and maximizes mileage and comfort by using all the torque available. In S it delivers more response for the same gas-pedal application, doesn't shift under heavy cornering loads, and downshifts sooner; as in manual mode, downshifts are rev-matched for smoothness and longevity. In Manual mode you select the gear you want, ideal for winding elevation changes where you know what's coming and want to save a lot of shifting, in traffic to better control speed, or on long descents to save the brakes for stopping.

Most A4s come with quattro, Audi's all-wheel drive system. It makes acceleration easier and has differential locks for best low-speed traction. The default split sends 60 percent of engine output to the rear wheels for better driving dynamics and balance. The system is completely transparent to the driver and requires no action. All-wheel drive is more effective for acceleration than traction control because the latter achieves grip by reducing the accelerative force of the front tires. But remember that all-wheel drive merely provides accelerative force to propel the car, and to a lesser extent steer it in low-traction conditions. It does not repeal the laws of physics and uses the same tires and brakes to slow the car.

The A4's brakes deliver impressive slowing even on a wagon with a load on board. Outright stopping performance depends a great deal on tires so we're guessing the Sport package cars might stop the best. An electronic parking brake, operated by a switch on the center console, can give close to maximum effort when needed and hold a decent grade.

Weight and its distribution play a part in virtually every aspect of a car in motion. Most of the A4's suspension pieces are forged aluminum, as is the front crossmember; the anti-roll bars are hollow and the steering rack has been positioned for less weight in the moving parts. The rear suspension is sort of a small-scale A6 setup with toe-control trapezoidal links and separate spring and shock mounts that allow a lower floor but more suspension travel, a win-win situation. Also for better balance, Audi mounts the battery in the trunk.

More significantly, the longer wheelbase of the current model pays huge dividends in ride quality, stability, steering reaction, and braking. With the wheels farther apart and carrying closer to equal weight it's easier to make each do its own share of the work, so despite the nose-heaviness caused by the engine and driven front wheels the A4 feels lighter than it is and surprisingly adept at swallowing bumps and road imperfections while still delivering decent cornering. With quattro it's even better, and the wagon's extra weight over the rear wheels makes it entertaining.

Our first exposure to the A4 was in a base-model Avant 2.0T quattro Premium, meaning automatic transmission and generic tires. We were sent out on an active racetrack ahead of Mazda's sportiest RX-8 R3 and behind Audi's mid-engine R8 super-sports car running hot laps. The next six miles were laugh-out-loud fun as the R8 never got away and the RX-8 never caught up. In short, we were chasing an R8 in a station wagon. Of course, we're excellent drivers but it was plainly obvious the new A4 is a superb road car, one developed and tuned by people that commute at 130 mph.

Over a few hundred subsequent miles we found the A4 equally capable on any road. Longer wheelbase means more time between the bumps and everything gets smoother as wheelbase lengthens. But it never becomes soft or mushy and an impromptu speed bump test that began at 20 mph and progressed to 50 mph rode better the faster we went.

We really couldn't find any behavior the A4 does wrong. Yes, the electronic stability program intervenes on some roads because no stability system reads the road ahead, but it can be dialed back in increments to reward the smooth driver. On Sport suspension and tires the ride goes firm but never stiff, and the fun quotient goes even higher. At the highest level, the Drive Select system with dynamic steering and variable damping that calculates shock rates 1000 times/second gives the widest spectrum, from comfort-like a base car on 17-inch wheels to stick-like a Sport on 19-inch wheels, and you can program one mode to your liking.

We would advise caution considering 19-inch wheels for bad roads like you may encounter in the rust belt, or Arkansas I-40. They look great and stick well but cost a lot to replace when you bend or break them.

Outward visibility is good in all directions, aided by low-profile rear headrests, sensibly sized pillars, fog lights front and rear, and good wiper coverage (including the rear in the Avant, with dual washer jets). More expensive models also benefit from bi-Xenon headlamps that adjust aim at more than 75 mph, a backup camera with parking assist, and side assist for lane changes.

The A4 is also quiet to allow hours behind the wheel without fatigue. Despite the largish outside mirrors wind noise is hushed, road noise is kept to a minimum and the engine is heard only when you're working it.

The 265-horsepower, 3.2-liter V6 offered last year has been discontinued to make way for the return of the S4, now powered by a supercharged 3.0-liter V6 producing 333 horsepower and 325 pound-feet of torque. Like the turbo-four it's fueled by direct injection and breathes through four valves per cylinder; additionally the V6 employs a two-stage intake manifold for maximum flexibility. An optional active rear differential overdrives the outside rear tire in corners, forcing the front end to turn in more quickly. It also communicates with the vehicle's Drive Select system and stability control to help maintain control in emergency maneuvers.

With a six-speed manual transmission, the 2010 S4 rockets from 0-60 mph in just 4.9 seconds, which is quicker (by 0.4 seconds) than even the previous-generation manual-shift S4, which was powered by a naturally aspirated V8. And fuel efficiency is greatly improved, with the 2010 S4 achieving 18 mpg city/27 highway, compared to 13/20 for its immediate ancestor.

The S4 is also offered with Audi's seven-speed S Tronic automatic, wherein the top three gears are overdrives. The S Tronic uses dual input shafts and dual clutch packs to execute computer-controlled gear changes in just one-fifth of a second. Zero-to-60 time is exactly the same with the automatic, while highway fuel economy improves slightly, to 28 mpg. Both versions of the S4 are electronically limited to 155 mph.