From the factory, the Audi S4 is well balanced. Standard features include large brakes with twin-piston calipers, a powerful twin-turbocharged V6 motor, and a street suspension to harmonize the S4's overall performance. The stock suspension is soft enough for easy long-distance travel yet is sporty enough to handle most Audi enthusiasts' appetites for handling performance on twisty roads.
As you will come to see, the goal of this project is not to build an S4 race car but to take each of the performance categories to the next level. We may have gone a little overboard with the massive, 355mm Stoptech brake system, but if there's a category that has room for extra performance, it's braking.
With the excessive dive characteristics the Audi was displaying from the additional braking power, it was time to beef up the suspension. In addition to the dive under braking, newfound horsepower (to be featured next time) had us looking for a suspension setup that would help reduce squat while keeping the S4's ride totally streetable for everyday use. Eibach Springs was contacted to help us.
Known for its long involvement in various motorsports, including rallying, Formula One, oval and touring cars, Eibach Springs offers a plethora of suspension components and full suspension systems for a number of European cars, including Audi-so it didn't take long to narrow down our search. The company is an actual manufacturer of suspension systems, not simply a marketer. "With our kits we are reengineering the handling, not just improving the ride height," said Eibach's David Royce. "All of our street kits are tested to ensure the best performance in real-world, everyday driving."
The testing doesn't necessarily include just lap-time comparisons. According to Royce, a lot of information can be extracted simply from a car's feedback with the new suspension, the way it feels. Royce stated, "If it feels better, handles better and rides better, it must be better." But if you're into lap times, Royce reports he tested a stock Ford Focus at Buttonwillow Raceway and shaved off 7 sec. per lap, the only upgrades being Eibach's suspension and Toyo T1-S tires.
For Project S4, we desired a street suspension and chose Eibach's Pro Kit springs, Pro Damper shocks and an anti-roll kit, comprised of a front swaybar only. Eibach reports its Pro Kit springs are a moderate increase in stiffness over stock, depending on damper forces and the way the car feels. When customers order a simple spring set from Eibach, they can rest assured those springs will be tested with O.E. shocks to make sure the car is not bouncing around and hurting handling performance. I was curious as to the reasons for only including a front swaybar and not a rear, but Eibach said it was more of a safety issue against too much oversteer. "Imagine you're going around a looping onramp pretty fast and find stopped traffic in front of you; we want the customer to feel when they brake hard in a turn they won't get too tail-happy," said Eibach's James Hickerson.
As mentioned before, Eibach is well known for its variety of springs and spring rates. If a race suspension is what you desire, Eibach also sells its ERS (Eibach Race Springs) line, as featured on Project M3 (see ec 12/01).
Since this was Eibach's first full suspension kit for the S4 here in the States, the technicians at Eibach took Project S4 for a few days for some further R&D to make sure the car didn't sit too low or ride too harshly. Three days later I picked up the car and was absolutely pleased with the results. Project S4 dropped by over an inch, giving it a much more aggressive look without being too low for the street. Driving it back to the office yielded no surprises-there weren't any new creaks or rattles, and the ride was surprisingly gentle. At highway speeds, I brake-checked the car to see how much the nose would now dive, and it was much better. Sure, it still dives a bit but nowhere near as much as before, where I almost worried about bottoming out the headlights.
Throwing it around a few oval onramps revealed much more neutral handling characteristics than before. The car was very difficult to snap into any kind of oversteer, even with the most sudden of throttle movements or brake applications around a turn, keeping it pretty safe for the more inexperienced driver. One might think that with a suspension system this forgiving it might understeer too much. But for street use, interestingly enough, the car felt more planted and surprisingly neutral. Maybe that has something to do with a slightly stiffer rebound from Eibach's new Pro Damper shocks; either way, the car is much more fun to drive and even safer to throw into the turns without getting yourself into trouble.
If more oversteer is what you prefer, you can do away with the front Eibach swaybar. You might even go crazy and take out the front factory swaybar altogether if you really want to go like Colin McRae!
In the end, Project S4 received a suspension kit that was a several steps up from the stock suspension, able to handle the braking power and the increased horsepower I'll talk about later, yet it's still totally street friendly. The car now has a much more aggressive stance, combined with a ride quality that's smooth as freshly laid asphalt. But even though we're focusing on street-specific upgrades, don't think for a second that Project S4 won't visit the racetrack in the near future. Just for kicks, we'll see how this street stuff does under harsher conditions. But next we'll talk about the BMW M3-eating power Project S4 is now making. Stay tuned.