Shocked Into Action

This article was first published in 2001.

Yes, this is a story about fitting a car with new springs and shockers.

No, it's not a story that attempts to be objective, to be sprinkled full of measurements tying bump and rebound rates to damping forces and shaft velocities. If you want a story about the latter, consult the three stories that we have run on damper dynos. And if you want to know about a suspension upgrade that quantifies handling and braking performance improvements, well, we've already covered that as well.

Instead, this is the story about one man - that's me - and his car. And it's on what I decided to do about the shock absorbers that were well and truly worn out. The symptoms of an aging suspension, the choice of replacement parts, the installation process, and the end result make for what we think is a very interesting story in itself.

The Car

The car in question is my '94 Audi S4 (or is it a '93? - built '93, imported by Audi Australia in '94 and registered in '95. And, according to the US Audi S-Car sites, it has various bits that make it a '95 model... so who knows?) Despite having only 100,000-odd kilometres on the odometer, the suspension - and specifically, the dampers - felt very old. It's worth going into this in some detail, because even the car in which I have done the most kilometres - a '91 Subaru Liberty (Legacy) RS - never felt like it had worn-out suspension, even with 150,000-hard driven kilometres on it.

But the Audi was different.

Like the Subaru, it uses a north-south mounted engine powering four-wheel drive, and also like that Japanese car, the result of this configuration is that the engine is completely ahead of the front wheels. However, the Audi has an in-line turbo five-cylinder that uses an iron block, while the Subaru uses a much lighter all-alloy flat four. The result is that the Audi is forward weight biased, and that hammers the hell out of the front dampers. It probably doesn't help that I drive the car hard enough that front tyres last only about 15,000km, and the rears seldom more than 20,000...

If you don't know of the car you won't be alone - there are very few of them in Australia - but in standard form, the large four-door runs high 14-second quarters; it's no slouch despite its meagre 2.2-litre engine capacity.

Anyway, after 100,000km of hard driving, I could detect some major symptoms of damper wear. And what were those symptoms? It's worth going into some specific detail, because this is a topic often brushed past.

Firstly, it needs to be said that if I didn't routinely drive lots of other cars, I would have been much harder put to spot the degradation. However, especially when I recently drove for a week the similar-concept (tho' executed much differently!) current model Audi S6, stepping back into my own car immediately confirmed that things weren't as they should be. Other cars that I have recently driven that showed really good damping control include the Saab 9.5 and even - in a much different way - the Lancer Evo 6.5.

Specifically, the ride in my car was much poorer than it should have been (not only in the car continuing to bob after a bump, but also in that wheels tended to fall with a crash into potholes - rather than simply dipping into them); the handling on bumpy roads had become so bad that it was verging on dangerous (again specifically, I could get the front to literally hop 25cm sideways at 100 km/h around marked 50 kay corners); while the handling on smooth bitumen was still fine but with much more pronounced entrance understeer and a kinda floppy exit power oversteer. But note that the smooth road handling was still quite acceptable - the tyres were wearing even more than usual and the car was sliding around more than I remembered it ever doing, that's all.

And, even when driven sedately, the more people packed into the passenger seats, the less damped the ride felt.

So, it was time to do something about it.

Choices

Now, here's where the theory hits the reality. I know that "damper rates should be matched to spring rates". What that actually means in terms of the numbers, no one has ever actually been able to tell me. I know that a slightly shorter stiffer spring (Er, how much shorter? Er, how much stiffer?) will give handling benefits, while with the right dampers, the ride will suffer barely at all. However, turning that into real life is a much harder task.

Without dyno'ing the dampers (which dampers, anyway?) and then consulting lots of knowledgeable people, the ascertaining of the desired spring specs (ie free length, rate, pre-load, captive length) would be damn-near impossible.

If I had a Holden, I'd have approached the people who make complete aftermarket Holden suspension kits by the truckload. If I had a Japanese car, I'd probably look to Japan for a complete kit (actually I wouldn't: Japanese aftermarket spring rates are notoriously way over the top in stiffness). But with a German car I figured I could waste a lot of time and money trying to come up with something unique - when all I had to do was to go to some German aftermarket springs and dampers.

Which is what I did - Eibach springs and Bilstein dampers. Not adjustable - what I got was what I got. But at least they were specifically designed for my Audi, rather than someone's best guess about a car they had never heard of. The Eibach springs were model number 1516.140E (boxed as the "Pro" kit), while the dampers were Bilstein B49-2066 and P36-0369. The springs cost $550 and the dampers $802 (GST inclusive).

Research

One thing I did do was look very intensively around the web - always a good approach when you own a rare car. There are lots more Audi S4's in the US than in Australia (and I guess even more in Germany, though I have never found any relevant German websites on the car) and several of the US S4 sites have sections on suspension. However, some of the data is confusing, while other is contradictory. (Worryingly, no sites ever mention the fearsome steering kickback over harsh bumps that is such a downer with the car - but that's another story. And one that I'll be tackling next...)

However, many of the sites suggest that the Bilstein dampers are the best way to go (whew! that's one I got right) while the Eibach springs are also good - although the 'Pro' series are now apparently hard to get. I don't know if I got the 'Pros' because - despite the box labelling - the model number is slightly different to the quoted 'best' ones.

Anyways, apparently lots of other people have fitted Bilstein dampers/Eibach springs and have been happy.

However, assessing the worth of what others say gets even more confusing as it's said that the '92, '93-'94, and '95-'96.5 Audi S4's all have different spring rates. Which one mine is I don't know (cf earlier my mention of the car's plated dates and the extra standard equipment which it apparently shouldn't have). And, in the way of many enthusiasts' web sites, the glowing praise sometimes isn't related to specific models - so whether the Eibach/Bilstein upgrade is good on all of the cars or only some of them, who knows?

In fact, interestingly enough, apparently anything from 170 pounds/inch right through to 340 pounds/inch rated springs were used at the front of this body shape - the variation being related to different engine and model combinations. Which would mean that going from an Audi 100 to the Eibach spring kit must be a helluva bigger jump than upgrading from the S4....

One other odd aspect about the web data on suspension on this car is that at least a number of people have found the need to make modifications to the upper front damper mounting plate - drilling new holes to turn them into aftermarket camber plates with more than the factory limited adjustment. In fact, when I first skimmed this web page stuff - which even had pdf-file full-size templates for redrilling the plates - I figured that lowering the car must give radically bad camber. However, when I later read the material closely, I found that the enthusiasts were actually complaining that the Bilstein/Eibach approach gave the fronts a neg camber of about 1.5 degrees.

Now if I were asked to specify the best neg camber (taking into account the trade-off between reducing understeer while prolonging tyre life) for a constant four wheel drive car, I'd pick very close to this figure - so I couldn't for the life of me see what the fuss was about. Without the re-drilling and tapping of the factory plates, people were complaining that they were wearing out the inners of their front tyres - but obviously they simply weren't driving hard enough around corners... Living at the top of a bumpy mountain I couldn't see that being a problem for me!

Anyway - could I get the dampers and springs? It turned out that I could: Broadwater Brakes and Suspension on the Gold Coast ordered in the parts, and I waited.

And waited.

The springs arrived and I duly went down to admire them; the dampers were nowhere to be seen.

I waited some more.

Around 3 months later, everything was in the one spot. The quote at this stage was $1700, which included the supply of the components ($1352), a four-wheel alignment, and fitting. I figured on a few extras - maybe a bush here and there - and perhaps a bit more labour than expected (I was sure that they would never have seen an Audi S4 before) and thought that the bill could quite easily reach $2000.

Fitting

The first step was the check the alignment of all four wheels. Note that while people talk confidently about having dialled in what are really tiny changes of geometry, you'll find if you take your car from workshop to workshop, each machine reads slightly differently. Further - and it's something that I'll come back to shortly - bouncing the car up and down often makes significant changes to the measured values....

The reason that the alignment values were checked before the suspension work was undertaken is that lowering a car usually changes these angles - and sometimes even just removing and replacing parts can alter the alignment.

Anyway, onto the machine and the Audi had the following specs:

	Front Left	Front Right	Rear Left	Rear Right
Camber	-1.0	-1.3	-0.2	-0.9
Castor	0.8	0.5	-	-

	Front	Rear
Toe-in	1mm	5.9mm

To briefly make sense of these figures, negative camber is the angle that the wheels lean inwards at the top (and 1.3 degrees is perhaps just visible to the naked eye), while toe-in is the amount that the wheels steer inwards to the car's longitudinal centreline. A rear toe-in of 5.9mm is excessive, while a front toe-in of 1mm is probably less than ideal.

However - and here's the critical bit - these figures are for when the car is stationary... just sitting placidly on the alignment machine. In real life, as the car is travelling down the road, it's never like that. Instead, the car is diving under brakes, squatting under power - and furthermore, has people sitting inside. Place a body weight into the driver's seat and the Audi's front camber changed to being equal left to right. Hmm, interesting. But even more intriguing is that pulling down hard on the front of the car (ie replicating the body movement under braking) caused the toe to change from 1mm of toe-in to 3mm of toe-out! Even more startling is the 5mm of toe-in that we could replicate by lifting the nose of the car to simulate acceleration!

The very soft dampers obviously increased the ease with which the body could be moved up and down - but the lesson is clear that taking notice of just the static wheel alignment values is telling little of the story.

Once these figures had been gathered, the Audi was shuffled off to another hoist to have its bouncy bits excised.

The rear coil-over suspension strut was easily removed - three top bolts and a single lower one.

A special wall-mounted spring compressor was used to allow the safe and easy removal of the spring.

Spring off, the new and old could be compared. (The 'new' is cleaner!) It can be seen that the Bilstein is shorter than the original...

...while the new spring is the same length as the old but uses a variable rate design.

The original dust cover (incorporating a bump stop) did not firmly fit on the new damper, so a power steering boot was used instead. Note that the Bilsteins have internal bump stops. Making sure that the shaft is completely sealed against dust will reduce the likelihood of failure.

The new rear damper and spring in place.

Next the front struts could be tackled.

Again the tricky spring compressor was used. Note the massive lower section of the strut... Mr Audi sure didn't want this bit to flop around!

The replacement front spring is noticeably shorter than the original....

... while the new damper boasts a massive shaft diameter and like the rear damper, is slightly shorter than stock.

Some oil was added to the strut to provide a thermal path between the damper and the strut housing...

...the retaining cap for the damper was treated with a dose of Loctite,

...before a special tool was used to screw it into place.

The original dust boot could be re-used, and so this carefully positioned...

...before the strut was re-assembled and bolted back into the car.

After a few circuits around the block to initially settle the suspension, it was time again for the alignment machine.