I have the Bilstein Drop links. So i’m a bit confused by the « Expert Mode »😃 of this thread.

i supposed they are correctly installed , i did almost 5 trackdays with them without any trouble.

Do you think DropLinks can be the reason why its bouncing ?

i don’t feel the rear too much stiff... the problem is at low speed, on a bumper, once going down the rear seems to make ondulation... Up/down/Up
sorry its hard to explain

 

If you have anyone near you that has a DSC, see if you can test it in your car (it takes about 2 minutes to swap). I am pretty sure you will be impressed with the change in how the suspension reacts.

Ed

 

Drop links and sway bar will not affect the "bouncy-ness" of the ride. Unless you hit a bump at one corner only....


To clarify my setup, referred by to my shop notes. I do have preload on the rear passenger side only in order to achieve my corner balance

 

Where can i find a DSC ?

 

https://www.tpcracing.com/product/ds...v3-controller/

 

Not to belabor a point (and only trying to help) but IMHO the recommendation is for ideal traction of the tire - both street and track. Going through a curve at 50 mph is the same whether that curve is on the street or the track, same asphalt. You lose traction at the higher pressure AND tire becomes improperly stiff. But experiment and find out for yourself: in the middle of your drive, stop and check the pressure. The hot pressure in the rear should be bled off to about 35-36.

The above recommendation is from Michelin, but if you search rennlist Porsche racing forum you would find the same thing stated. Run Cup Tire at 35-36 PSI when hot. Cold pressure would be even lower IIRC about 32 PSI or so. This is what I did when I had my Pirelli R comp (similar to your Michelin Cup).

 

Hi - this forum had discussion about the Bilstein Damptronic's bump stop 10 plus years ago so its existence is well known. Sorry my writing was not clear; let me try again.

You had recommended "changing bump stop" and my caution was that for the Bilstein Damptronic hitting internal bump stop ti to the degree that you need to change it is essentially unheard of when lowering is within specs, and per Bilstein changing the bump stop is 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?

 

There is no problem with the bump stop.

Most if not all shocks have them. A coilover is just a shock with a coil spring around it/ over it hence "coilover". Some are ride height adjustable. All shocks which come with a bump stop use them.

You can replace the bump stop just like you can replace your tires, or rubber bushings, etc. You can pick a long or short, hard or soft, or any combination of bump stops. Changing them is a valid tuning option, racers, auto crossers and hobbyists alike all change bump stops often. Discussion for the street is not really made often.

I would very... very, very much recommend changing the bump stops on bilstein shocks. Its cheap and incredibly easy to do, and yields a noticeable effect.

Lastly I answered your question with the coilovers I am using. They are custom valved H&R street shocks. H&R uses a digressive bilstein piston made to their spec. I have had mine modified I cover it in the post I linked.... which I have linked again below...

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

I also made another post to discuss "Shock Tech" and to begin to explain why "you" "we" have the experiences we have with aftermarket parts:

https://www.6speedonline.com/forums/...long-read.html

 

Undulating motion, like an under-dampened system? But at low speed, when hitting street bump?? You could try DSC as already suggested, but I would recommend a local pro's test drive and input as best and safest approach at this point. I have no further input sorry (primarily because subjective description cannot be relied upon).

Your Bilstein drop link that comes with the kit is still rubber/plastic, not the same as drop links with metallic heim joint like from Tarett https://www.tarett.com/items/996-997...lnk-detail.htm. Any metallic joint replacing plastic joint in suspension components tends to tighten movement and makes action more immediate, at the cost of increasing NVH. Best analogy I could think of: Imagine being hit by someone wearing very soft glove vs a boxing glove. Force is delivered faster, with no softening (metallic doesn't "give," plastic/rubber does give and soften the force). I've taken drop links on and off my car many times to study its effect on street feel: yes it does reduce loose motion in the rear. You could try the Tarett drop link front and rear since it is cheap and easy to take on and off to study for yourself (people who race cars love it). Whether it solves the soft undulating motion I have no idea, but even if it doesn't I think you are going to love it so it won't be money wasted.

Besides tightening suspension action AND improving subjective street feel (firmer and tighter), Tarett drop links also allow proper elimination of preload on the sway bar.

 

Thanks for explanation. You're using the sway bar's preload to achieve corner balance? Not by adjusting height/coilover's preload?

 

Yes and no. I use the height adjustment of the coilovers to get the desired ride height. Then I use the alignment adjustments in combination with the endlinks to achieve corner balancing. I want as little spring preload as possible in order to have as much suspension travel as I can. In my case it is roughly 3.75 - 4" total suspension travel. This makes it work very well over bumps, and at the ride rate I am running occupies the lower end of track performance. I daily drive mine on bad roads so I had to be selective about how I wanted things setup. In order for me to improve the setup for the track I would need functional aero and then maybe 10% more high speed damping. As it is I am running at 0.5 inches per second I am at 80% of critical and at 3ips I am at about 55% critical, my shock forces continue to taper and then blow off pretty flat after 6ips.

I decided to share a shock dyno for my fronts. The blue line is the final, the others are labeled for what they are. Factory NON- PASM, H&R off the shelf, and then the revisions to final for my fronts.




Also there is no such thing as "Proper elimination of preload on the sway bar". IF you are using pre load on the sway bar it is to correct a particular steering behavior, or for corner balancing. Else any preload would be unnecessary if you did not have a steering issue or if you don't care about corner balancing.

 

Thanks for sharing. Interesting (but I must say IMHO, very strange) approach to corner balancing and using sway bar.

How did you test the alteration from H&R off-shelf to your revision? By improvement in time trials at the track?

 

It is not strange at all. It is novel to you. Here is a blurb from Milliken and Milliken Race Car Vehicle Dynamics



I have done AutoX with the stock PASM shocks with lowering springs (previous owner mod). Then with my custom coilovers, my AutoX times went down by about 3 seconds.

Here are additional references to suspension preload:

Spring preload:

All about sway bars:

Sway bar Preload tuning:
https://www.joesracing.com/setting-the-bar/

"Whether you use a standard one-piece bar or a three-piece big bar, your sway bar will work more efficiently if you mount the link that connects to the lower control arm at 90 degrees.

Upon arrival at the track and with your car race ready it really pays to set up your scales on the most level ground you can find. Shim the scale pads if needed and mark the pad location so that you can weigh the car at the track in the same spot. Once the scales are set up, weigh the car and record any difference that might be created due the track ground not being level as compared to your shop set up. By establishing a baseline at the track, you will be able to make adjustments and use your baseline to maintain proper loading of the bar, ride heights and wedge. An established baseline will help to get you back to your desired numbers even after many trackside changes. Check the sway bar at the track, with the car on the scales, and note any difference in preload as compared to when you set the bar in the shop."

https://www.hotrod.com/articles/ctrp...-spring-setup/

"Sway Bar Preload
One benefit of using a sway bar is that it helps us get more bite off the corners. Sway bar preload, actually pre-twisting the bar, increases this bite effect. It also causes an increase in the crossweight percentage. It is best to put in preload and then set the correct crossweight in the car. That is opposite the way teams have usually done their sway bar preload, but we need to know exactly how much crossweight is in the car when we race it. If we set the crossweight and then preload the bar, we don’t know where our crossweight is."

 

Thanks for taking time to explain - nice work. How about between H&R stock and H&R modified? Huge improvement also?

Miliken seems to mention in "Asymmetrical Effects" stabilizer preloading one side of the car is advantageous in closed race course's environment, where you turn only one way (left or right). Does this mean this approach does not work for a street driven car, or at AutoX?

 

They mention road courses too, in the same paragraph. I simply included it as a for example sake for racers using sway bar preload to tune cross weight load transfer // corner balancing // making corrections to a steering behavior.

I did not test the H&R stock because in my opinion it has too much total damping making it stiff, jarring, or harsh. I have had similar setups on other vehicles I have owned. The graph I supplied a few posts ago show the stock H&R on a shock dyno and you can see it has a very large amount of rebound. Because my car is not aero dominant there is no need to pull the chassis into the bump stops and hold it there. I need to leverage the mechanical grip of the vehicle and utilize suspension travel. I have no real need to compare the stock H&R to the custom valved.

If you were close to me I would say come on by and we can go for a spin, you'd be able to see that the car handles very well but does not feel harsh or "bouncy"