Anything else modified in the car's suspension system? Stock sway bar? Stock rim? Which tire are you using?
What are the tire pressures when cold? How much lowering (vs stock) - hopefully not too much more than 10-20mm?

Bouncing "too much" with Bilstein: no, of course it's not "normal". But what is "too much" is quite subjective in that what I think is normal, you may think is too much. How smooth is the road/what kind of road you are driving on when this "too much" bouncing observation is made? At what speed?

Ride vs handling is a trade-off. Don't expect a race/sport oriented suspension to behave like stock. It will be stiffer than stock and ride won't be as smooth. It's in the corner that it will win, not on rough roads. Hope this helps.

 

When I acquired my 997.1 with PSS9's I had the same comment, but since I had PASM, and did a bunch of reading, I purchased a DSC module and it made an immediate difference.

Does your car have PASM?

Ed

 

As I just got finished saying in my previous post. Sway bar will not cause that. "Bouncing too much with bilstein" doesn't mean anything. Any poor setup can feel bouncy or actually be too high of a ride frequency, it is not dependent on brand. A change was made without understanding what would be changed. In this case the car already pulls itself into the bump stops AND uses lots of damping to in essence "trick you" the driver into believing your setup is now better because you can feel a difference: http://farnorthracing.com/autocross_secrets19.html

Ultimately we agree that how a suspension setup feels is unique person to person. The only person who is able to tell us if it is "too bouncy" is the driver experiencing that behavior.....

 

Actually, i just changed the coilover and the links (included with the coilover)
the tyre pressure may be a bit lower , 2,7 Bar for rear.
Ride Height: i left the basic height of the new coilover.
Tyres: Michelin Cup 2

And still PASM on the car.

 

If you have PASM, I strongly recommend getting the DSC unit. It changed the nature of the suspension more than any other single change I have ever made on ANY car.

Ed

 

Ok it could be a solution, but if the PASM is Off i suppose it doen’t affect anything ?

by the Way, i don’t know why it feels so bouncy... can’t imagine the nurburgring edition of pss10 by Walter Rhor are so smooth

 

PASM is never off, just not in Sport mode. DSC makes full use of the active suspension functionality. Your springs can also contribute to the feel, but the inputs into the active shocks from the unit are what really make the difference. When you lower the car you shrink the travel length available to absorb the undulations so you are already making it tougher to be compliant and firm.

I was surprised how "bouncy" my car was with the coil overs, to the point I was looking at other options. The DSC has put that off for a while, though going with the Tractive Suspension components will be something I do in the future.

Ed

 

Sorry for slow response; I rarely read this forum anymore. All IMHO:

1. 2.7 bar = 39 PSI correct? Is that hot or cold pressure? Either way that's way too high for Cup tire's pressure. This means your car will feel very stiff and you might even be sliding all over the place . I am no expert but Michelin Cup should be around 33-35 hot (NOT cold). When I had my Pirelli R comp (similar to Michelin cup) I routine was in the low 30's hot.

2. What do you mean by "links"? You mean drop links? Take off the link and use stock link. The drop link does a great job if you are looking to reduce rear motion, but it does increase stiffness. Take it off if car feels too stiff for you.

3. Let's confirm one last time : Please explain again what you meant by "bouncy" - you meant it's too stiff right? Not bouncy as in too soft up and down undulating motion?

4. The stock Bilstein, IMHO, is not stiff at all. In fact it was still too soft for me and I had to change to stiffer springs for it to approximate GT3 feel (since then completely happy and have not touched the system for years). If you think it is too stiff then something is wrong, or we just have a completely different idea of what "stiff" is (nothing wrong with this - personal preference). You might also want to check sway bar to make sure it's not frozen and the drop links are installed correctly. Lastly I'm sure you already know stiffer coilover is not meant to be running high speed on rough roads - it's meant for high speed cornering on smoother surface of the track for example. Any bump on the road at high speed is going to bounce the car more than the soft stock suspension.

5. Stock PASM algorithm of the Turbo affects Bilstein differently, in a good way. The Normal-too soft/Sport-too hard behavior should be gone. Normal should be just right for street, and Sport slightly/moderately stiffer (should be for track IMHO). You should not "need" DSC but YMMV. Hope this helps.

 

-Drop links connect the sway bar to either side of the car. They do not provide stiffness. They put an approximate pre-load on the sway bar, giving you roll resistance. Not vertical stiffness.

-Stock Bilstein in normal mode is "soft" because the stock springs are fairly light targeting a ride frequency of below 1.3hz. In "Sport" mode they just crank up the rebound a bunch to make you feel a difference and marketing tells you stiffer is supposed to be better.... Which is not exactly true. If you personally think stiff is good, like how stiff feels, etc then by all means make it a kidney punching ride...

-You are correct, with aftermarket coilovers the vast majority of them run too much damping force overall. They also tend to run much more rebound, which does favor flat tarmac and high speed cornering (depending on the high speed rebound/compression). With much stiffer springs and much slower shocks (Stiffer shocks = slower shocks) a bumpy road will just not feel good. There is no way around it. If you tune a setup for flat road it will be great there but not really anywhere else. Vise versa, you tune for bumps and you'll walk away from someone on bumpy roads, but find you want more damping on a flat aero dominate race track.

 

1. I'm talking about after-market vs stock drop link. Do you have after-market drop links with metallic joints like these Tarett's? https://www.tarett.com/items/996-997...lnk-detail.htm I believe that's what the poster has, and that's what I am talking about.
2. ???: Sorry if I misunderstood but this is opposite of what I know . You don't want any preload when setting drop link no?. How do you install your drop link (loaded or unloaded wrt car weight)?



Not to imply at all that you didn't have problem with yours, but per Bilstein rep (I talked to them quite a few times way back when) and based on numerous users' reports over the years: this is unnecessary and not recommended in a properly installed shock for typical normal non-professional use. For the simple reason that shock and spring lengths are designed to prevent such. Yes hitting bump stop has been reported, but only when improper excessive lowering is involved - way above 1 inch IIRC. (Of course, also happens accidentally, like not seeing and accidentally hitting a road bump at extreme high speed; but that's expected/what the bump stop is for.)

 

Random internet search for Mich Cup tire pressure below. I think we may have identified the first "problem" with your setup: too high pressure 2.7 bar = 39 PSI (is this hot or cold pressure?). So IMHO this is the first thing I would do - lowering the tire pressure, by a lot . For comparison, when I had R comp tire (Pirelli), I had to run pressure so low that the tire pressure monitoring system would be triggered and I got low pressure alarm continuously.
R comp tire like Michelin Cup has extremely stiff wall vs. normal street tire (partly why lower pressure doesn't cause tire to deflate/collapse, and partly why it feels so "good" ). The Cup's tire compound itself MAY be softer (for more traction or whatever), but the sidewall is much much stiffer. Once hot, tire also becomes overly slippery if you over-inflate. So on many aspects, you need to lower that tire pressure.

>>>>>>>>>>>>>>>>>>>>>>>>>>
https://rennlist.com/forums/991-gt3-...endations.html
Just noticed manufacturer recommendations for MPSC2 tire pressures
INFLATION PRESSURE ADVICES
On the track for majority of car (*)
Cold tires
• Inflate the MICHELIN Pilot Sport Cup2 with a pressure between 1.7 bar (24 psi) and 1.8 bar (26 psi) front & rear
• Never allow the pressure to be below 1.5 bar (22 psi)
Hot tires
• The optimal operating pressure of the MICHELIN Pilot Sport Cup2 must be between 2.3 bar (33 psi) and 2.5 bar (36 psi) Front & Rear
• Never allow the tyres to run below 2,0 bar (29 psi) HOT

 

The sway bar being connected with drop-links always has some amount of pre-load. It is a combination of the length of the drop-links and which hole you are using on the sway bar arm. There is no right or wrong approach to preload. In normal street driving it probably will not benefit you.

To answer your question I have SPL drop links front and rear. https://www.splparts.com/products/fr...er-cayman.html I installed the drop-links with the car in the air and the suspension loaded to the length I had the links at. My notebook is at the shop so I cannot tell you off the top of my head what I went with front and rear. I can say that I have some pre-load on the rear sway-bar and little to non in the front. However the specifics of my setup contribute to the whole as I have targeted a ride rate of 1.9hz front and 2.3hz rear. The front has more compression than it does rebound to support the outer tire and so the front sway bar for me is no longer unnecessarily stiff. The rear has slightly more rebound than compression so that the car settles quickly between turns and or bumps. I have a fair amount of toe in and the middle setting on the eibach rear sway. The car rotates very well and there is no snappy feeling to steering while on the edge. The car is as close to neutral as I can get it, if anything there is a slight amount of low speed oversteer and high speed understeer. Which is what I want.

All Bilstein shocks come with a bump stop. (Yellow / Vanilla colored thingy at the top)




All non custom Billstein shocks have more rebound than compression which over a series of bumps will pull the chassis into the bump stops. This is by design, which is "ok" there are many ways to skin a cat. The same can be said about the use of bumpstops altogether. If the car is at the correct ride height you will engage bump stops moderately (unless you have some really stiff springs). If you lower your car with lowering springs and not height adjustable coilovers you will basically be bouncing around on the bumpstops.

Just as a point of clarity bump stops are supposed to be used. They do matter quite a lot. It is why you can place packers on your shock's shaft to remove travel in order to change handling of your car at a specific corner. You can "tune" the use of the bump stops by using very stiff springs or shocks, thereby never engaging them (not recommended). Or you can use a moderate spring rate and use a softer bump stop and use it in combination with the shocks to assist in the deceleration of the chassis.

 

1. Thanks for clarification. Interesting discussion. Not an expert but must admit this is first time in many years of reading/asking that I hear anyone putting preload on sway bar. Porsche guys on racing from always talked about eliminating preload as a major point of using after-market drop links. And adjustable length means which hole should not matter. Anyway, how do you know how much pre load you are putting on/do you actually measure the preload force? And why would you want to have preload - now sway bar is exerting force even when you're driving straight, no? Seems to me preload would alter intended spring action/rate, and left right balance if uneven left to right. (My tuner actually specifically recommended against this (preload) btw, but you seem to have a different system approach?)

2. Sorry if I caused some confusion (I am aware of the Bilstein bump stop, no picture needed. ). You had recommended "changing bump stop" and my caution was that for the Bilstein Damptronic hitting internal bump stop is essentially unheard of when lowering is within specs, and per Bilstein not necessary/recommended for intended use. Just curious which coilover you're using that is causing problem with bump stop? Is it designed for the Turbo?

 

1. Shocks and springs respond to changes in velocity. Anti roll bars respond to displacement. The primary reason you see people wishing to eliminate pre-load is that you want to run as little anti roll bar as you can. Eliminating pre load is as close as you can get to running a disconnected roll bar. Changing the length of one or both end links changes the behavior of the sway bar + car. For instance you can cause the car to steer in a direction when launching, which is useful if the car does not launch in a straight line. Otherwise you preload the roll bar to add roll resistance without having to change bar sizes or mounting points.

2. To answer your question of what I am running, I posted about it here:
https://www.6speedonline.com/forums/...ould-care.html

There is absolutely no way Bilstein would tell you bump stops are not intended for use if they include them with their products.

 

For me this is the recommandation for a trace use.
My problem is on the normal road... ans i’m quite sure Michelin’s recommandation are différent for street use