whale driver

The previous owner of my 89 S4

had installed huge rear sway bars that really keeps the car level in serious turns. My issue is that the ride is very harsh. The photo shows an attached rod that appears to allow adjustments to be made (see attached picture). Which direction (lengthen vs shorten) should I adjust the nuts to soften the ride?

Speedtoys

Sway bar wont soften or harden the ride.

That would be springs or shocks.

Those look OE, perhaps Bilstein shocks...they are a rougher shock than the OE Boge shocks.

Wisconsin Joe

Those look like Ott links (or a copy).

The length of the rod won't affect the ride. It's adjustable so that when you dial in the ride height, you can then make sure there's no stress on the sway bar at 'level'.

Any adjustment to the apparent stiffness comes from where the link rod attaches to the end of the swaybar.

There are a couple holes that can be used. To soften the bar, attach the links as far from the bend as possible. Make the part that comes back as long as possible.

But Speedtoys is mostly right. Ride harshness or softness is far more due to shocks & springs than the swaybar.

There's a link to the installation instructions for those somewhere on here. It was posted when I got a pair of those links from Mark and asked.

Speedtoys

..well, what about a sway bar makes the ride rougher? From what I can tell, its the OE bar as well.

Wisconsin Joe

It does look like the factory one.

A stiffer swaybar will transfer impacts across the car to the other side. A bump that should only affect one side will affect both.

It's secondary to the shocks and springs by a pretty large margin, but it's there.

SeanR

Your harshness is due to the Bilstien shocks, not the drop links.

Those also appear to be Eibach springs, and that just makes an entire world of mess with those shocks. I would change the springs to stock (cheapest option) and try again.

FredR

The rear links may have some impact on the apparent harshness if they are not set correctly. There are two positions- stock and stiffer than stock. They were intended to provide a quick and easy means to modulate the built in understeer of the stock set up. It does this by changing the effective bending radius. Reduce the radius and the rear bar will effectively stiffen and in the stiffer of the two positions will reduce the stock understeer to a more or less neutral characteristic- that as I understand was Louie's intent when he designed these items.

The adjustable height is there to remove pre-load. The stock drop links are not adjustable in length and if the car is running stock ride height this is not an issue. However, if the ride height is lower than stock that introduces an element of pre-tension. Thus the idea of the height adjustment is such that with the car fully settled the mounting bolt should be able to slip in and out with no effort when it is undone. So, to get the correct adjustment, with the car settled you undo the bottom bolt and adjust the length of the link until the bolt slips in with no resistance- the car sitting on its wheels taking the full weight.

The harshness you complain has much more to do with the suspension units. It looks as though those are Eibach springs mated to Bilstein dampers. The Eibach springs are progressive- i.e. non linear- the more they compress the spring rate increases some. Nominally they are 25% stiffer than stock springs. .They were. developed by Kim Crumb to give the best of worlds for cars that were occasionally tracked and mostly street driven without having to go to the lengths associated with coilover change out.. Different folks have different opinions about them and they are welcome to them- my opinion is that they work superbly considering the design intent. Not sure I would want to use them on roads full of potholes. Couple the spring rate with 18 inch wheels and lower profiles and the ride quality will not suit everyone. Over here we have excellent roads so no issue. As with most things there are no free lunches and the benefits have to be weighed up against the debits.

As for performance all I can say is that on the Dubai Autodrome a Porsche factory instructer pulled me over after I literally waxed his tail in the 996 twin turbo he was driving. He could not comprehend the way my 928 was cornering.The factory team organising the event were fascinated by this as they had the concept that the 928 does not handle on the track- well it does. Kim personally taught me how to setup the car- it works! Drive over one of those short sharp speed bumps and you quickly wish you had not! I put that down to the Bilsteins. I changed out the front units for Koni internally adjustables and that was a big improvement. One of these days I will change out the Bilsteins on the rear - for sure this suspension is not for everyone but for those who know what they are doing and what they want they are [were?] a great upgrade.....

whale driver

Can anyone tell me what springs manufacturer and stiffness I have from the imprinted number in the attached pictures? Front: 928 int frnt 113045 rear: 928 113 245 rear

Kevin in Atlanta

Eibach produced for 928 International.

GregBBRD

There's a whole bunch of "Internet Myth" about 928 suspension, shocks, and springs.

There's four different "main" things that affect stiffness of both the front and the rear suspension, going straight down a street and hitting a "bump" with both wheels at the same time. Shocks, springs, bump stops, and control arms. The sway bar will affect the stiffness if you hit a bump on only one side, at a time, so if this occurs, there are five things that affect stiffness.

The amount of people that have sat down and spent the time to really analyse the suspension, calculate the wheel rate compared to shock rate, figure out the actual spring rate, figure out how much the rubber bushings affect the spring rate, figure out the bump steer ratios as the car moves up and down, figure the amount of travel on the shocks on either end of the suspension, figures out at what ride height the bump stops become "active" is tiny....really, really tiny.

I'm not going to dive into the myths of the 928 suspension, nor how it actually works, here. I'll just give you your main problem and you can correct that, drive the car and see if you like it, when you are done.

The springs on your car are not only stiffer, but they also lowered the car. There is so little suspension travel (especially in the front) that the front shocks are hitting the foam bump stops 100% of the time. The actual shock absorber has such little travel that the valving (brand controlled) is virtually moot, because there is virtually zero travel. There's a way to increase the amount of shock travel in a 928, but no one (I know of or have heard of) has looked hard enough at how the pieces work and interact to know how or what to do to to be able to make this happen. (I do.)

The fastest and most logical/cheapest "repair" you can do is to take those springs out of the car and install a stock spring. Confirm that the rubber bushings in the lower control arm are not broken or breaking apart (very common, since these cars are now old.) The lower control arms are a huge percentage of the front (progressive) spring rate, when they are new and are able to twist. (Once they are worn, cracked, taken a set from the car being too low, they are junk.) Replace the bump stops, if they are destroyed (very likely.) Set the ride height to something reasonable that allows more shock travel. (So, this decision turns out to be super important. At stock ride height (180mm), these cars are just barely off of the front foam bump stops.....and look stupid. However, at 160mm, the "front spring rate" has gone absolutely "off the scale"....the foam bump stops are significantly crushed and have become a MAJOR part of the spring rate!) Align the car, set the tire pressures to reasonable levels, and align the car. The suspension will then be able to travel and the shock will actually do their job. (If you want/need the car to get to 160mm or even 150mm (or lower), you will need to change some pieces, in the front suspension, in order to get shock/spring travel.)

The Bilsteins are not doing anything in "compression" with the springs you have in the car....they are resting on their "internal" stops at the ride height your car is probably at. (140mm or below, I'm guessing.)The Bilsteins, if they are still functional, will work fantastic and will not be overly harsh, once you get the car raised enough for the suspension to actually have travel. The shocks in a 928 are actually a very small factor in ride stiffness, as they add/change very little, in terms of spring rate. As it turns out, different shock brands have different internal shock stops....this is extremely important to take into consideration!

GregBBRD

What the heck happened? Silence? All you guys with "theory" get overwhelmed with actual data?

Here's some "proof of life", for your data collection.....

Boge shock. Spring removed for clarity. I cut the "tube" off of the dust cover and left the top portion that supports the foam bump stop in place. New foam bump stop. White plastic washer left out, for clarity. Suspension height at 175mm. Vehicle level.


And NO! You can not just "cut down" the foam bump stop to create more travel...Konis and Boges have an internal mechanical stop (which a lot of cars are actually riding on or hit when going around a corner....if your car is at 140 or below, it "hits" this mechanical stop around almost every corner.) which limits the compression travel. (Try to imagine what the effective spring rate goes to, when the shock hits this mechanical limit...."infinite" comes to mind.) Interestingly enough, Bilsteins have an internal "rubber" stop (not a solid mechanical stop), with a bunch more shock travel before the rubber is contacted.....go figure why a Bilstein works better on a lowered car!

We are constantly trying to get people to raise their cars back up to "reasonable" heights, so the suspension can actually do what it is intended to. I had a GTS in, a week or so ago, which was set at 120mm. Needless to say, it was "rigid" and rode exactly like it was rigid....the springs could have been removed and thrown away.....they were doing absolutely nothing. Actual front spring rate was........infinite, sitting still.

whale driver

What are your specific chassis measuring points to determine the factory standard ride height of 175 mm? What size tires were considered in this measurement? I measured mine from the base of the jack pad to a level floor: front = 203mm, rear= 203mm.
My sway bars: Front = 31.3mm Rear 22.8mm.
I am running 17" rims with 225/40 & 255/50 tires

SeanR

Didn't have anything more to add. Already stated he needed to get rid of the Eibach/Bilstien combo. It sucks unless you are on a track. I dislike Bilstiens on our cars furthermore but that is just from personal experience and having to remove a bunch of them from customers cars as someone else talked them in to it. They disliked them also but love the Koni's or Boge's I put in as a replacement.

GregBBRD

When you change from Bilsteins to something else, the ride height always needs to be adjusted. I'm betting that you are "raising" cars, to more "reasonable" ride heights, getting the suspension off of the stops.

This is my point, in this discussion. 928's sitting on the bump stops are very "rigid". Once you put some travel back into the car and the shock gets a chance to actually "move", things get better really quickly.

Next time, before you just automatically say "Bilsteins are junk", raise the car and get some shock travel.back. Trust me, your "shock sales" will drop, considerably.

SeanR

You tend to make an awful lot of assumptions these days and put words in peoples mouths. Never said they are junk. I personally have zero use for them when I find Koni's do a better job. IMHO. Doesn't really matter as I doubt Bilstien will produce anymore anyway. That's a good thing to me as it means I won't have to swap out that many more when people take other peoples suggestions as gospel and find them selves disappointed.

Anyone who spends anytime working on these cars suspensions knows the above. You are saying that my "shock sales' would drop but I'm not in the parts selling business, but I think you already know that. I've installed a single set of Bilstiens in the past 6 or so years after doing so on mine and I hated it. Koni's or Boge for me, unless specified otherwise, so far no one has jumped. If a customer has a car set at factory ride height and hates the ride of the car after someone else put bilstiens on it because it's too rough, too jarring and they generally hate it Imma do what the customer wants. Get rid of the rough, harsh, jarring shocks and put something on there that they would feel more comfortable with. And this has happened 3 times in less than that many years. One of them came from Ca and it was under your advisement to use them. That car I put Koni's on set at M and he is very happy, over the moon happy. I promised not to name names so won't. One of those cars is sitting in the garage right now and I asked him today how the ride was and he still loves it a year later with factory Boge's and stock springs. I did use one of those sets of used Bilstiens and used them to replace a customers well worn sport shocks and he's happy with them, he should be because it didn't cost him $1000.00 in shocks and he drives it like it's on the Nordschleife daily.

As I said at first, this guys issue is the spring/shock combo. Get rid of those Eibachs (we know those drop the suspension by a good amount) and he very well may be happy with the B's.