76FJ55

This statement is NOT correct.

Weight transfer happens regardless of suspension set up. Weight transfer is a product of CG height, rate of acceleration (lateral or longitudinal) and wheel base/track width. You could design a car that has 0 body roll but you will still have weight transfer. The following generalities may be made here:
increased wheel base decreases weight transfer(acceleration)
increased track width decreases lateral weight transfer
decreased CG height decreases weight transfer.

you can have any degree of roll stiffness and the weight transfer will not change provided the CG stays the same.

tv

That was a direct quote from some guy who claims to have 30 years experience racing Porsche's and came from this article - as I already posted --

http://rennsport-systems.com/events/...1-suspensions/

but who cares, I am not a science major, just want to enjoy driving my 928 with the best possible attributes possible.



From what I have read so far, my somewhat lighter 85 euro would probably do best with a ;

Front spring rate....................Rear spring rate..................shocks

1200 ....................................600 ..............................Koni FSD



Seems this would give the ideal street ride, no dive, no roll, and non-jarring absorption of all bumps/holes.

76FJ55

[QUOTE=tv;7690566]That was a direct quote from some guy who claims to have 30 years experience racing Porsche's and came from this article - as I already posted --
[QUOTE]

Sorry, it was meant to be an attack on you or the original writer. I have just heard this statement made numerous time (not necessarily on this forum), and thought I would try to correct this misconception. Just trying to pass on what little knowledge I have.

tv

No problem here is another post from an enthusiast at a BMW forum, just what we are looking for, these FSD's sound great;




My goal was to improve ride comfort and handling at the same time (seemingly impossible as they're opposing suspension traits). I don't track or autocross so, I don't need coilovers or anything that extreme.

My ride comfort went out the window after I switched to 19's and also the car looked stupid unlowered. I drove about 10 E46's (local BMW club) with different suspension setups, PSS9 on different settings, Eibach/Blistein, H&R, K&W, BC... and found them all to be way too harsh for daily commuting.

Then I came across the FSD's promising to deliver what I was looking for and boy did they! After I got them on, ride comfort went back to when I was on 17" and stock suspension, BUT, at the same time, the car handles A LOT better. Low frequency movements (like turns) are damped hard and low frequency movements (like bumps) are damped softly. I can take the same corners at much higher speeds with more confidence as the car stays relatively flat. At the same time, bumps that used to make me wince are now totally acceptable.

Of course, some of it has to do with the Eibach Prokit springs that went in at the same time.

So car is lowered and looks good, ride is comfortable and handling improved by a few leagues. The perfect compromise for me.

I would say: Go for it!

tv

Just found an interesting shot and realized some logic.


If we all drove on a surface like this everyday, a perfect smooth racetrack, we would not even need shock absorbers because there would not be any shock (bump up or hole) to absorb. Most of us have driven a go-cart on a track.


(save pics if you want them long term as some are links)

ptuomov

I think you'd still need dampening as long as you have any springs. The springs would compress and expand if for no other reason because of steering input.

tv

So we need very stout springs to keep roll and dive to a minimum BUT we have to be able to ABSORB the shocks of the road surface. It seems that everyone has been trying to cure the absorption problem by compromising on the roll/dive area with softer than ideal springs and even trying to customize inferior shocks. Seems like the FSD has the tech ability to do the job FINALLY of absorbing shocks in the surface w/o jarring.


Here is the Mercedes SLS AMG suspension, the one that is setting world records for handling, look familiar?????





(SLS curb weight - 3573lbs)

No reason why the 928 can't handle world class TODAY with the correct stiff springs and a capable shock!

tv

it would be extremely minimal with very stiff springs, springs that would not roll on hard circular on-ramps or dive in a panic stop from 75 mph.

dr bob

Simon is correct, and points to a detail in the referenced info from Rennsport. In that reference, they suggest a shorter or cut-down spring to stiffen the suspension and reduce weight transfer. Note that the redction in weight transfer comes almost completely from the 'shorter', not so much from the 'stiffer', all related to CG starting and staying lower.

Back to the discussion!

tv

Well that's good in that we already have a low CG and 928's look better with a lower than normal stance anyway a la Mark Robinsons black car. With shorter (and stiffer) springs and hopefully lots of adjustablilty on the FSD shock like Mike S has on his it could be a win-win.

BC

Anyone contacted Koni to see how many shocks would need to be purchased to get the FSD? A million? A thousand? Anything close to our needs already produced?

ptuomov

No response. There's not even a catalog on the web with fsd shock dimensions that could be used to find shocks that might work in our cars.

BC

I noticed when I visited. So much for "online presense" and "contact management" for Koni. Big F for them.

tv

I don't think they would care about 1 customer inquiry. Koni make the FSD shock in our format and the make the shock body for 928's already. So there is no added expense for them to make these available to the 928 customer base.

If these work as Koni claims - like an advanced high tech electric shock - if they work as well as enthusiasts of other cars on other boards claim and as well as Hacker has heard - then this seems to be the only shock that you should buy. It could be the trick that puts the 928 back near the top handling wise.

If all of the 928 vendors called the same sales rep/executive at Koni and said our customers want the FSD, I see no reason why it would not happen.

Here is the format we need pictured on the box the bmw guy received his FSD's in, lower middle;

Okv

May be possible to find a (FSD or similar technology) shock, and make adaptions like on my BM5 set-up.

From what the BMW-man says, it kind of resembles the PASM on the Cayman.
The Cayman has relatively soft springs (almost like the 500/350, front 1.32 Hz / rear 1.38 Hz NOTE - VERY APPROX), but still feels stable and solid in the sports setting.
PASM means electronically controlled shocks, and you can select between a soft and a stiffer sport setting by pushing a button on the center console.

In soft mode the car is comfortable, far more than the shark, still kind of driveable, but some soft in damping.
In sport mode it really tightens up, but it still does not feel harsh, as it seems like the smaller irregularities and bumps gets absorbed, while body motions due to turning and braking is significantly stiffer and more controlled.
At first, when I got the car, this felt very strange, kind of like driving a car with too soft shocks, but with the performance in handling and stability of a car with a really stiff suspension.

As the sport settting only affect the behaviour of the shocks and not the spring rates, the static body roll and pitch movements are the same.
Ideally I would like some stiffer springs on this car to reduce body motions further, but when running on street tires it is not so bad that I feel it is required to change anything.
And the softer springs are nice on the snow, where it is also mostly best to drive with the soft setting on PASM.

There is a Bilstein Damptronic PSS9 available for the Cayman, it seems to have freqs around 1.55 F and 1.65 R.
Perhaps an indication that this is the sweet range - 1.35 to 1.65 Hz, and that the rest of the necessary stiffness could be achived using better, new technology shocks.

(Please do note that the frequencies I have stated in my posts may be not be very accurate, though they can give us a clue to what we are dealing with here.)