Bilsteins too soft - how to revalve?

[kermac]

G'day AudiZiners

I'm reposting this on the B5 Forum as I'm not getting any replies on the Suspension and Brakes Forum.

Anyone know anything about changing the valving in shock absorbers to make them stiffer?

My apologies - this turned out rather a long post.

--------------------------------------------------------------------------------

G'day

Long-ish post. Stick with me

I wonder if anyone has any knowledge of revalving or adjusting Bilstein shocks?

Background

I have a B5 (2000 model) 1.8TQ Sport (we call them GP Series Down Under). The factory Sports suspension seemed abormally high, especially at the front. A friend offered me a set of used Eibachs off his '98 model.

I thought I would follow the advice of the gurus and upgrade my shocks at the same time , which would help prepare the car for the occasional track day.

No one was able to tell me in advance how much the Eibachs would lower the ride height as there was no way of telling whether the stock springs were atypical or from a bad batch, or perhaps there was a problem with the height of the spring perches? I checked with the owner's handbook and found they were indeed Sports springs, not Heavy Duty or Cross Country. Truth is, the car looked like a Toyota LandCruiser at rest

The Choice

I wanted a shock that was both height-adjustable and had (at least) rebound adjustment. Of course, No one makes such a beast.

I'd had Yellow (Sports) Konis and Eibachs on my previous A4TQ. The original owner of the car had fitted them right out of the box without adjusting the settings, so they were....well.......soft. I bought a Koni adjusting key and went out one mild Saturday morning to tweak 'er up.

PROBLEMO: you have to take Konis off the car to adjust them, which with my limited expertise and almost non-existent workshop facilities meant taking the car to a professional. Anyway - the end result was pretty good. I just didn't feel like paying a suspension fitter another $300 each time I wanted to tweak them a little to get them to my exact requirements.

So - I deleted the Konis from the list this time round.

The only other entry on the (very short) list was Bilsteins. These can have grooves machined on the body so you can move the circlip that locates the spring perch, thus altering your ride height up or down by up to 20mm BUT - Bilsteins are non-adjustable for stiffness

The purchasing and fitting experience

I live in Australia's capital city, and although small, we are lucky to have a suspension genius who managed the whole thing. He even got the Bilstein agent to ring to enquire what sort of springs I was using, and how I wanted the shocks set. "Reasonably firm", I said, "but not enough to rattle the kidneys. And I'll be doing the odd track day, so plenty of control if you please."

"No wukkas, mate*" said this eloquent fellow.
*Aussie argot for "no wukkin' furries, my good man"

So the suspension genius got the shocks the next week, I left my car with him for the day and all was well witht he world. I marvelled at the new ride height when I picked up the car, and drooled over the negative camber at the front. So we'd certainly got it right in the looks department.

Driving impressions

At first, the car seemed so much better to drive - really good turn-in going into corners, seemed to stick to the road like glue. But after a bit I realised I hadn't tested the suspension out properly by taking her for a hard drive on poorly-surfaced country roads.

The picture changed completely. On bumps or potholes, the front suspension would crash and jar your teeth. On large bumps or undulations, the back would wallow and pitch and take several cycles to settle. The I had to do a bit of a crash stop where the surface was a bit rough, nothing special, and the car was all over the road. Rounded a corner with a bump in the middle and the back end wallowed and started oversteering.

In short, these shocks are only good on smooth roads. On rough roads, they're far too soft both on compression and rebound (although I'm not certain whether the crashing at the front might not be caused by the fronts being too stiff on compression. The suspension guru thinks otherwise).

The problem (you still with me??)

I've discussed this with said guru, and agreed the Bilsteins need revalving. The problem is - revalved to what? How do you quantify your needs and convert this into valve settings on both compression and rebound? There is, you see, a price to pay (like life, really). $300 or thereabouts each time you have the shocks removed and replaced (luckily I kept the old shocks so there won't be too much downtime).

How do you make sure that you get something close to what you need without repeated visits to the guru?

I should add that I finally realised just how soft my rear shocks were when I went for a track day with a friend and his B6. He has coilovers with relatively hard springs (I think he said 800 kg/cm front, 1200 rear) and the rebound setting on the dampers close to the max. His handling was brilliant (both to look at and from inside the car). The back of the car was almost rock-solid. On mine, I could grab the towbar and bounce it up and down like a baby's stroller.

Needless to say, I haven't yet had my car on the track

Ideas, anyone? Is there any sort of database on axle weights / spring rates / damping force??

Thanks for staying with me

kermac
Canberra, Australia

[maxspeed]

coilovers.

[kermac]

coilovers.

I know, I know .

While your suggestion does have the virtue of brevity, maxspeed - unlike anything I've ever written in my life - it is also the most $$$ solution.

I should have fitted COs from the start, but I had a good deal on the Eibachs and had heard great things about Bilsteins. In the long haul, a spring-shock combination will probably have a longer life than the coilover, but of course they lack the range of adjustment the top-end CO has.

I don't believe there's anything wrong with the Bilsteins that re-valving won't fix. The tech at the Bilstein agency just misread my request and assumed I wanted comfort at the expense of anything else. Can't think why he did this....

Anyway, I'm going to stick with my present combination as I know it can be improved. The question is - how to quantify my needs in a way that can be converted into appropriate damping settings?

[urS4]

I have had experience revelving Bilstein Sports in another Audi application, a 93 urS4. Several years ago, I was running Eibach Pro Kit springs and Bilsteins. The car had a fairy strong engine good for about 420hp/430q ATWs. It also had Big Reds on all 4 corners with a custom 26mm sway bar in the rear and a factory 26mm bar in front. It ran good at the track but was a little soft. I went with coilovers in the rear with heavier linear springs and had the Bilsteins revalved to +10% bump and +30% on rebound. They worked wondefully and were a great street/track compromise. COs were not an option at that time but last year the urS4/6s got a couple of choices. I ended up going with a very expensive but no compromise CO kit that included dual adjustable, on the car, Koni Motorsport shocks. We also went with a 28mm front bar from the S6+ and I had a new 28mm bar for the rear fabricated. I have springs for the street and for the track along with ride height adjustment. I ended up selling my old suspension to a local guy and he absolutely loves it. The most important aspect of the revalve is the increase to rebound. This worked on a heavier car, 3685lbs dry measured during corner balancing, and it just might work on yours. This car is being rebuilt right now with a 2.5 liter stroker motor, new tubular exhaust manifold, Big Valve and Big Cam Head, and a new ITS 271 daul ball bearing turbo. It should be a lot of fun.

[kermac]

Thanks urS4!

I was aware that increasing the rebound rate is the key to increasing control without making the ride unbearably harsh.

I think I may also need to increase compression (bump) rates a little while increasing rebound rates a lot.

Your post has been helpful in giving me some sort of numbers to talk about. Those percentage figures for bump and rebound - what are they percentages of? I mean, does 100% on bump mean the shock doesn't move at all?

[kermac]

The car had a fairly strong engine good for about 420hp/430q ATWs......... This car is being rebuilt right now with a 2.5 liter stroker motor, new tubular exhaust manifold, Big Valve and Big Cam Head, and a new ITS 271 daul ball bearing turbo. It should be a lot of fun.

You have a fine sense of understatement, sir

[urS4]

Good question. It refers to the change in bump and rebound from their original valving from Bilstein when the shocks were new.

Thanks urS4!

I was aware that increasing the rebound rate is the key to increasing control without making the ride unbearably harsh.

I think I may also need to increase compression (bump) rates a little while increasing rebound rates a lot.

Your post has been helpful in giving me some sort of numbers to talk about. Those percentage figures for bump and rebound - what are they percentages of? I mean, does 100% on bump mean the shock doesn't move at all?

[kermac]

Thank you.

Of course, the worst part of trying to get the suspension sorted is not the cost but the inconvenience - having to leave the car in the workshop all day.... take a taxi to work from the other side of town and back......and then do it all over again in a week or two when the revalved shocks arrive back from the dealer in The Smoke.

I'd be more confident that his revised valving rates would work for me if he'd got anywhere near the mark the first time round. What I've got at present is a car that's dangerously underdamped except on dead smooth roads