2007 Audi RS 4Click to enlarge picture

A powerful, sophisticated, high-performance sport sedan, the Audi RS 4 possesses a perfectly balanced chassis and excellent steering.

2007 Audi RS 4

Produced by quattro GmbH, Audi's performance and tuning subsidiary, the RS 4 is the first RS model based on the Audi A4 to be sold in the United States. Germany-based quattro GmbH has a goal to build the best performance vehicle in each segment, and the RS 4 can certainly be called one of the best sport sedans that the subsidiary has ever offered.

The RS 4 Avant and the RS 2 Avant that preceded this new sedan were both sold only in Europe. The first RS model in the U.S. was the RS 6 Avant, based on the A6 Avant and powered by a 450-horsepower bi-turbo V8 engine.

On paper the RS 4 seems to have every angle covered: a 420-horsepower 4.2-liter V8, a 6-speed manual transmission, 14.4-inch front discs with 8-piston calipers, quattro all-wheel drive with a new Torsen center differential, 19-inch alloy wheels with 255/35ZR19 Pirelli P Zero or Michelin Pilot Sport tires, and Audi's next-generation Dynamic Ride Control (RDC).

Although some cars don't translate well from paper to pavement, the RS 4 does not suffer this indignity. Out in the real world, which for us included the Angeles Crest Highway and Willow Springs racetrack (Is that the real world? --Ed.), the RS 4 doesn't disappoint.

If fact, the RS 4 is so good from a performance standpoint that it's hard to find any faults. With abundant power, subtly aggressive styling, precise steering, a perfectly balanced chassis and a high-level of Teutonic luxury, the only bone of contention is the price of entry—which is steep—beginning at $66,000 and reaching $73,000 in the version that we drove.

The RS 4 Is a Serious Car
The RS 4 is the kind of car that expresses its capabilities from the moment a person slips into the driver's seat.

From the way the contoured Recaro seats hold the driver in place to the feel of the three-spoke steering wheel to how easily the gear shift falls to hand, the RS 4 promises a high-level of performance even before the engine starts. And with a turn of the key, a swift selection of first gear and a squeeze of the throttle the experience continues to improve.

One of the surprises of the RS 4 is its captivating sound, although it shouldn't have been any surprise since the S4, the other high-performance version of the A4, has a very purposeful burble from its 340-horsepower V8 engine. But the RS 4 has an exhaust rumble unexpected from a European sedan.

And with the "S" (sport) button on the dash engaged, the sound gets even better. The sport mode produces a more aggressive exhaust note as an accompaniment to a quicker throttle response.

Both the RS 4 and the S4 have 4.2-liter V8 engines, but essentially the only things the two engines have in common are the bore and stroke dimensions—the RS 4 engine is completely new, beginning with the aluminum alloy engine block, aluminum alloy cylinder heads and FSI direct injection that was developed on the Audi R8 prototype race car that won the 24 Hours of Le Mans for five consecutive years. A twin exhaust system with larger pipes adds to the engine's higher power output.

The RS 4 body also looks similar to the S4, but as with the engine very little is shared—only the roof and the front door panels are the same. All other body panels are exclusive to the RS 4. The hood and front fenders are aluminum for weight reduction, and brushed aluminum is used for the grille surround and the outside mirrors. The ride height is 1.2 inches lower, while the front track is 1.5 inches wider and the rear track is 1.9 inches wider, necessitating larger front and rear wheel flares.

Other exclusive body elements include a unique bumper design, black mesh grille material, flared side sills, a rear spoiler integrated with the trunk lid and rear fenders, oval exhaust pipes, 7-spoke 19-inch wheels and RS 4 badging.

Despite all the changes, the RS 4 carries enough resemblance to the A4 that a casual observer might mistake it for the more basic sedan, but an informed enthusiast would know the difference. Admittedly, much of the subtlety is lost if red or yellow is chosen for the exterior color, but the overall package is still fairly discreet for the level of performance delivered.

Driver's Car—Technology Doesn't Interfere
Part of what makes the RS 4 a true driver's car is simply this: the technology doesn't come between the driver and the driving experience.

The Dynamic Ride Control (DRC) system is purely mechanical—not electronically controlled—and functions without any intervention from the driver. No need to choose the sport suspension setting when you want to push the car hard or the comfort setting for daily driving—the DRC makes the adjustments as needed.

The asymmetrical/dynamic quattro system in the RS 4 is also mechanical, with a Torsen limited-slip differential that distributes power to the front and rear axles as needed depending on driving conditions. The torque is delivered 60 percent to the rear axle and 40 percent to the front under ideal conditions; however, up to 100 percent of the torque can be sent to one axle if necessary.

The latest generation of Audi's Electronic Stabilization Program (ESP) is designed and configured specifically for the RS 4, and any interventions occur later in the event and for a shorter duration, giving the driver greater control. The ESP includes front and rear electronic differential locks (EDL), traction control (ASR), electronic brake force distribution, and an anti-lock brake system (ABS). A two-stage defeat for ESP is offered to either eliminate the traction control or to deactivate the system completely.

Driving on the tight, twisting two-lane roads in the San Gabriel Mountains north of Los Angeles, we had the opportunity to experience just how good the RS 4 really is.

With abundant, usable power over a wide rpm range due to the broad torque curve, the RS 4's engine revs easily to reach its maximum output of 420 horsepower at 7800 rpm and beyond to the rev limiter at the 8250 rpm redline. More importantly, the V8 also delivers 90 percent of maximum torque from 2250 to 7600 rpm, which makes the RS 4 extremely tractable in a variety of driving conditions.

All this power does come at a price: fuel economy ratings are 14 mpg city and 20 mpg highway.

Even with the RS 4's impressive power and acceleration, the overall chassis balance and precise steering are what stand out the most. Steering is quick, precise and as good as any car we have experienced. While the steering does not offer as much true feedback as we might have found in a high-performance car 20 years ago, the rack-and-pinion steering with Servotronic electronic power assist responds instantly to driver inputs and delivers excellent directional stability on all types of road surfaces.

The DRC reduces body roll and pitch by connecting the dampers diagonally through a central valve. The RS 4 also has wider front and rear tracks than the A4, and we found body sway minimized and well controlled during acceleration, braking and cornering.

There is virtually no detectable understeer, even at the handling limits, which can probably be attributed to the rear bias of the quattro system combined with the excellent chassis dynamics.

Although some might wish the RS 4 was a bit lighter, Audi has managed to keep the weight to a respectable 3,957 pounds for the U.S. version while still including amenities such as power rear windows and available rear side airbags, which are not available on the European version.

At Home on the Track
On the track, the overall performance of the RS 4 is further amplified. Without the constraints of traffic laws, the laws of physics are the only ones that apply.

Willow Springs racetrack is very fast and provided an excellent opportunity to explore the limits of the RS 4. Even on the track the car was totally predictable and easy to drive right up to the limit. But to be fair, the cars that we drove at the track were fitted with R-compound tires—the equivalent of street-legal race tires.

Not only do the massive 14.4-inch cross-drilled and vented front discs with 8-piston calipers and 12.8-inch rear discs with single piston calipers do a great job on the street, they were equally up to the task of stopping the RS 4 from 130 mph lap after lap, with no perceivable fade.

The engine pulls strong right up until bumping against the rev limiter at 8250 rpm, delivering smooth, strong power and brisk acceleration even at triple-digit speeds.

That said, the precise steering and the excellent balance still leave the biggest overall impression.

The Ultimate Enthusiast Sedan
If the RS 4 has a fault besides its cost, it would be that it's just too easy to drive at excessive speed. The car is so incredibly capable and drivable that speeds well above the posted limits seem routine.

The BMW M3 has been the benchmark in the high-performance sport sedan category for nearly two decades, and Audi offers a formidable competitor with the S4. But the current M3 is several years old, and the RS 4 takes the high-performance sport sedan to a whole new level.

The RS 4 is a perfect combination of performance, luxury and balanced driving dynamics—it may be the ultimate high-performance sedan.

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