Chiming in with my perspective (a lot of it) here. Take it for what it's worth...
I will never put coil-overs on another daily driver. Here's the story.
I bought a C7.5 S6 in October of last year. This car has the air suspension which pleases me to no end. I will never have to "guess" how my car is going to feel after I spend a ton of money on it again.
I came from a B8.5 S4. I had 4 suspension combinations on it, some very expensive and was ultimately never completely happy. The following are the summaries of each:
Completely Stock: I was basically happy with most aspects of the ride. The car did not come stock with electronic ride control so it was what it was... And it worked. Cornered flat, dealt with harsh road conditions reasonably well for a car with 19s and 35-series tires, well-damped, fairly quiet. Basically, what one would expect from a sports sedan in this class. But the B8.5 especially, just didn't have the look I was after and I got the bug and started modifying it.
Suspension Setup #1: Bilstein B16 with electronic ride control: This setup got some things right but a couple critical ones very wrong. Having the ability to adjust ride-height meant I was able to dial the car in to exactly what I felt I wanted so this was great. I did not want a "slammed" car. I wanted a somewhat subtle lowered stance. And because the Bilsteins had isolation included, the car did not become noticeably louder with regard to road noise compared to stock. This was a win that I didn't realize the importance of until later. HOWEVER, the flaws ended up being more than I could tolerate. The suspension basically has three modes. Comfort, Auto and Sport. Comfort ended up being much too "soggy" and therefor unusable in my mind. And, even though ride was soft, I still noticed an increase in harshness over broken surfaces. Not great. "Sport" mode ended up being where I left the car most of the time because I couldn't deal with the soggy ride. But it was too harsh for my taste most of the time. Auto just switches "real-time" between the two based on driving habits and conditions. Nice in concept, not in practice. I never left it here because it seemed the adjustment was always behind. I did calibrate the system with the app, multiple times. No dice. It was never right. But there was a much bigger problem than the modes not really working for me. Rebound damping in the rear end of the car. There was simply not enough and the car would "buck" over large bumps and in certain conditions giving the impression that there was a lack of control. For this reason I would say that the car handled better for most conditions (especially daily driving) in stock form. This was a fatal flaw for this system in my mind and one Bilstein had no interest in helping with. The installing shop (which my brother owned) checked the car over several times and everything was installed appropriately. It should be noted that the different ride modes had very little effect on the damping issue. ANd since PSS10 is as I understand it, very similar but with manual adjustment, I would be very wary. And there will be more on Bilstein issues on S4 later in my post.
Suspension Setup #2: After being annoyed for as long as I could stand, I pulled he Bilstein off the car. At the recommendation of 034 Motorsports (who is local for me) I went with their lowering springs. They felt it would better meet my expectations. We went back and forth on which shocks I would use and we ended up deciding that we'd try the factory ones first and see how it went. And it was the right move. The car rode great. Almost as comfortable as stock. HOWEVER, there was a ride-height problem right from day one. My shop called me and sent pics - the car was at least as high as stock in the rear end. I didn't have a choice but to take the car back and see what happened. And while it settled some, it was not enough. The car had hot-rod like rake and the look just didn't work for me. Unfortunately 034 had no real interest (or resources) to get this right. It kind of baffled them but that's the extent of it. So off it went.
Suspension Setup #3: KW v3 Coil-overs: After doing lengthy research, more people recommended this setup than any other and I was at the point where I was willing to spend to get what I wanted. So I pulled the trigger and had my brother install it. Before I ever drive it his impression bothered me. It was stiff over the small stuff but soft over the bigger stuff. Now of course the suspension is completely adjustable, 2-way all the way around and so I took to doing so over the following weeks. And ultimately I got it to a point where I felt I couldn't do any better. This experience showed me that there is likely some flaws in dynamics of the suspension of these cars. As with the Bilstein, the front end of the car behaved relatively fine. It was the rear that provided the challenge. I ended up with very little relative compression (bump) damping (around 1 or 2 clicks out of a possible 12), and a ton of rebound damping (around 8 or 9 out of 12 clicks). And I would have gone higher on the rebound damping if I could. But more made the car ride real harsh due to the fact that suspension travel was impeded, I believe. At the end of the day, I was never able to adjust the harshness over small bumps out. I felt EVERYTHING. And while I could mostly live with the control over larger bumps which was better than the Bilstein setup, for the money it certainly wasn't perfect. And again, ride quality wasn't the only issue. Due to the lack of bushings/spring perches, there was a huge amount more road and mechanical noise. Keep in mind that I did do the 034 X-Brace and a couple of the chassis inserts at the same time as the KW's. I did specifically as 034 NOT to sell me the ones that I would notice this kind of thing from. So I don't honestly know how much of the added noise was from the inserts and how much was from the KW's.
At the end of the day, enough was enough. When I sold the car it handled well but added harshness and road and mechanical noise was too much for this 40+ year-old to handle, considering what started with. I do blame myself for some of this. I tend to over analyze this kind of thing and admittedly have some OCD. But objectively speaking, for the money I spent I should have been happier with the car.
What I learned from my B8.5: I don't like coil-overs for daily-driven street use. And I have a feeling many Audi owners will feel the same way. Too harsh and too noisy. Lots of variables, often high-cost and difficult to I'm now on my 6th Audi and almost every one I have modified suspension on has had issues. My first was a B5 A4 which I bought lowered. I think it had Koni's and I don't remember the spring but it was a street-comfort thing because the car was not real low. No shock, this car rode and handled perfectly with the exception of the inherent under-steer. The car was light, nimble and fun to drive and had zero harshness or excessive noise. A great daily-driver and a gateway drug for Audi.
But the 1.8T, even tuned as it was, was pretty gutless. And so I found a B6 S4 used and pulled the trigger. The S4 was stock until I decided to lower it. As it relates to this thread, I put street-comfort springs on the car and Bilstein shocks. It should be noted that, at the time, Bilstein did NOT have a SKU for the B6 S cars. Just the A. So they actually re-valved the fronts for the extra weight of the V8 and gave me A4 rears. Ironically, the front was fine but the rears were never right. And if you're guessing that the problem was the start of a theme, you're right. Rebound damping was pathetic! The car was never right and no amount of calls to Bilstein or tweaking by my shop helped. Overall, everything else was fine for my taste but the rebound problem tweaked me. Car sold.
Next car was a B8 S5. I could barely afford the car at the time. It was a City car and had been a bit abused. Paint was never great, had some rash on the wheels but from 10' away, was as beautiful a car as I had ever hoped to own. Plus the sound of that V8... But since the car was never in great shape, I never modified it. I owned it for 4 years, stock and loved every minute - until it started leaking heavily every time it rained. Weather dried out and I traded it in for the B8.5 S4. Considering my wife had my son while I owned the S5, the move to the S4 made sense. And as much as I liked the sound of the V8, the blown 6 was better in virtually every way.
Now to the S6. It's a 2016 Prestige and had a bunch of mods when I bought it and only 6500 miles. So I was able to do that critical "audition" before I bought and I found that the electronic lowering modules did not negatively impact the car at all. I drive multiple stock cars before I bought mine. The car does have EC sway-bars and end-links which are a little noisy but the added stability makes it worth it. I am genuinely happy with this car. It's the all-around perfect car for me. And again back to the point, if I did not have the air-ride I would be cautious about modifying. But if I were going to, I think I would go to a reputable manufacturer's street/comfort lowering springs. And personally, I would steer clear of Bilstein on Audi. I know they work on other manufacturer's cars but I've not had good luck. Koni has some good options and if you're not going too low or too stiff, the factory shocks can appropriately damp a mild lowering spring. I would not change any bushings or perches.
I think that if you're looking for what I do in my cars, near-stock comfort and noise levels, near-stock handling with subtle improvement, and with a stances that's improves the overall look of the car, over-doing it will net you spending a lot of money with the potential for frustration. I understand that everyone is different and to be clear, this is my personal experience and opinion. But I hope it's useful.
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Originally Posted by Rsniper4
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