You know KW. It's a household name among performance enthusiasts, known and respected for making some of the best suspension components in the world, offering both aftermarket and motorsport applications.

For our test, TAG Motorsports fitted the second Audi S4 with KW's Dynamic Damping Control system. This is KW's response to the latest performance cars with factory dynamic damping systems, allowing you to retain suspension adjustment functions but with the height adjustment of a conventional coilover system.

There are three damping modes to choose from at the touch of a button: Comfort, Normal and Sport. Comfort is great for poor surfaces or a highway trek, while Normal feels a little sportier than the stock S4, giving good control with acceptable comfort. The Sport setting is significantly stiffer and would seem most suitable for the racetrack.

The coilovers are part of KW's stainless steel "inox-line," able to withstand heavy use or salted winter roads. To reach the desired stance, TAG lowered the S4 to the point where some driveways and speed bumps were unapproachable. And this was where KW's optional HLS (Hydraulic Lift System) came in handy.

Fitted to the S4, HLS provides additional clearance for lowered vehicles by raising the car with a hydraulic cylinder placed on the coilover body between the spring and its perch. When activated via a console-mounted button, 45mm of lift is provided, gaining clearance for obstacles.

The KW DDC coilover kit retails for around $4000, plus an additional $3600 for the HLS system. This puts it well past the AccuAir system in terms of price, on par in terms of versatility. So which would we prefer?

The Test

To begin, we gained access to the top-secret test facility used by our sister magazine, MotorTrend, at Auto Club Speedway in Fontana, CA. They use a figure-eight test course to accurately measure lateral g-forces as well as lap times. With MotorTrend's road test editor Scott Mortara at the wheel, he put the cars through the identical test that every new car undergoes. And having driven everything on the road, Scott's feedback was invaluable to us.

The results of the test in the table (left) don't tell the complete story, but did fall in line with what we felt through our trouser dyno. The most important numbers were the average lateral acceleration g-forces, which is the measurement of accelerative force directed perpendicular to the direction of travel. So if you're driving a car and turn the wheel hard in one direction, the force you feel is lateral g. And more lateral grip means better handling. So while the differences are very small, it does show that the AccuAir system offered an improvement in grip over both the stock and KW-equipped cars

The figure-eight lap times are also very close; within a tenth of a second of each other. To put it in perspective, MotorTrend tested the Audi R8 V10 Plus on the same course and it set a 23.5sec time. More interestingly, its lateral accel was the same 0.99g as the AccuAir S4 on its grippy Continental SportContact 5P tires.

The KW-equipped S4 ran 0.1sec faster around the track, but we agreed the KW spring rates were too stiff and with another few laps, the air-ride S4 could be driven as fast or faster.

"The coilover car was disturbed more by bumps on the course and had similar understeer as the stock car," said Scott.

The stock S4 did exhibit lots of understeer at the limit, and the coilovers exaggerated this trait to an extent, making it difficult to get the car to rotate.

"The air-ride Audi S4 would be my overall choice," Scott claimed. "The ride felt good and initial turn-in was better than the coilovers, all the way through the corner and especially on the exit. I'd drive the air suspension every day," laughed Scott. And we would, too...

We found ourselves laughing because we weren't expecting these results, especially when we arrived to find the AccuAir S4 sat on the floor, with its wheels sucked into the fenders. Sure, it might look silly to some traditionalists, but it's a growing trend in the European tuning scene and something many enthusiasts are after. Yet with the press of a button on the touchpad, the car raises and calibrates itself in seconds to the appropriate driving height where it went on to handle (and look) the best.

So against all predictions and our preconceptions, the AccuAir car was the star of the MotorTrend figure-eight test. Now we headed to the hills to assess the handling under the toughest conditions.

Road test

Heading into the nearby mountains, the cars would be in their natural environment. The challenging turns and uneven road surface would be a demanding test for any suspension system, and this is where we expected the coilovers to claw back the lead.

Once in the canyons, we were able to gain speed, tipping into triple digits on occasions, experiencing everything from long sweepers to tight twisties. And yet the AccuAir system remained flawless. Road imperfections were absorbed without any disturbance, and the limit of adhesion was extremely hard to find.

Initially, we were surprised the air-ride wasn't crashing into potholes, and couldn't believe how flat the car cornered, with barely a hint of body roll. It also remained flat under acceleration and braking, giving excellent grip out of corners as the e-Level management ensured all four corners remained at the same height.

It was hard to believe that a car could drive this well on these uncompromising roads at very high speed, and yet would be able to raise itself over a driveway at our destination and drop itself to show off at an event...

In contrast, the KW DDC exhibited slightly more harshness even in its Normal setting - Sport was simply too stiff for these uneven roads, causing the car to become twitchy. However, even in Normal, mid-corner bumps could cause the front-end to transmit the disturbance into the cabin, with the rear-end bouncing along behind.

The coilovers also seemed to give less steering feel, and the overall agility was reduced when compared to the AccuAir system.

We felt the DDC kit might be improved with softer spring rates to reduce its tendency to bounce in corners. That said, the owner had dropped his S4 almost to its lowest setting, giving the suspension less travel than it might ordinarily have. Raising the car would doubtlessly improve the situation, but our test was to compare lowered cars on air and coilovers, so a lower ride height was part of the equation. And while the KW DDC did offer impressive handling compared to the stock car, we found that the choice of air suspension was a no-brainer in any situation, on any road.

These results seem truly remarkable. This day set a new milestone and will be remembered as the moment we learned to appreciate a well-developed aftermarket air suspension system.

It's clear that AccuAir's intention of redefining air suspension has been an overwhelming success. The company has created a system unlike anything else currently on the market, and unlike anything that we, as enthusiasts, have previously experienced. For the price, convenience, looks and dynamics, the AccuAir Sport air suspension system was the clear winner in our test.

The Cars

The two modified 2013 Audi S4s were built by TAG Motorsports in Escondido, CA and share similar components to give them great performance, handling and style.

They both share identical engine modifications, using an AWE Tuning supercharger pulley to increase boost pressure, as well as an S-Flo intake, exhaust and downpipes. The only real differences were that John Holdridge's black car had unresonated downpipes (and sounded better for it) as well as GIAC stage 2 DSG software that made it slightly more responsive.

The black S4 had the AccuAir Sport air suspension kit, and sat on 20x10" HRE P44SC wheels finished in Brushed Gold. Behind them was a 380mm StopTech ST60 brake kit that offered powerful stopping.

Dennis Tang's white S4 was on the KW DDC coilover kit with the KW HLS kit on the front. The fenders were filled with 19x9.5" HRE P43SC wheels finished in satin black as well as the same 380mm StopTech ST60 brake kit. Further differentiating the two was a EuroCode Alu Kreuz drivetrain stabilizer.

The exterior was kept subtle, in true Audi fashion, with both cars getting OEM Euro headlights, black grille and foglight grilles plus TAG Motorsports' blackout package. Additionally, the white S4 had gloss black exhaust tips and white StopTech brake calipers.

Car Lap Time Lateral Accel
Stock S4
AccuAir S4

KW Suspension
1075 North Avenue
CA  93657
Tag Motorsports
2181 Meyers Avenue
CA  92029
AccuAir Suspension
Grover Beach
By Alex Bernstein
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