Originally Posted by spf4000

What do you mean exactly by swinging? Are you talking about tram lining? That's when your wheels feel like they are getting tugged around by the grooves on the road. If that is the case, that has more to do with your alignment. Aggressive camber and toe-out on the front will do that.

Camber/tow is a compromise between straight line stability (less camber, toe-in) vs. turn in responsiveness and cornering grip (more camber, toe-out). The fix would be to first see where your toe settings are and if it's pretty aggressive on the toe out, then bring that in a bit. If that doesn't help, then reduce the camber a bit and you should be good.

On another note, I'm not a fan of lowering springs. Get proper coilovers instead of lowering springs if you can. Makes a world of difference when spring rates are properly matched with dampener valving.

Originally Posted by bbywu

Hard to judge whats happening based on your description.

Are you getting excessive squat and rear bias during your acceleration? Are you having oversteer problems on corner exit and difficulty with putting power down?

This could be because of insufficient rear spring rates for the power you are making. Oversteer on a corner exit is typically due to inadequate rear spring rates and excessive rear negative camber as you put the power down. Also, the overall sensation of "floating" could be due to insufficient spring rates over all, giving you excess vertical chassis movement, pitch and roll.

What type of aero do you have?

Originally Posted by bbywu

Hard to judge whats happening based on your description.

Are you getting excessive squat and rear bias during your acceleration? Are you having oversteer problems on corner exit and difficulty with putting power down?

This could be because of insufficient rear spring rates for the power you are making. Oversteer on a corner exit is typically due to inadequate rear spring rates and excessive rear negative camber as you put the power down. Also, the overall sensation of "floating" could be due to insufficient spring rates over all, giving you excess vertical chassis movement, pitch and roll.

What type of aero do you have?

Originally Posted by K24F

I took my 997 today, It's handling is really not good, while its Techart lower springs, GT3RS alignements and the PASM sport ON...
On track is it quite "correct" because the road is really proper, but on open roads or highways the car is "swinging" with the unperfections of the road, I hate that, even my M3 and my buddy's 997.1 4S with sport chassis handle better...

What is the solution? Sway bars (I don't think so...), new shocks? (my car is only 42000 km used) If yes, which ones would you prefer?

Originally Posted by cannga

IMHO what you are describing is a classic case of the ride vs. handling tradeoff in suspension setup. In general, a stiffly set-up car, whether by 1. springs, 2. damper, 3. tire, 4. sway bar, etc., handles better because of the reduction in weight transfer, whether front/back, or side to side (body roll). But what is the caveat? As the car become stiffer, at some point, it's going to start losing contract with road surface from road imperfections. This is why pro race cars are set up differently for different circuits (and what we cannot do): each track is setup for a perfect combination of stiffnes and road compliance.

More specifically to our Turbo, the first gen. PASM 1 in our Turbo has what is now considered a design flaw. PASM works by varying the dampening rate of the shock absorber; in the 997.1 Turbo, the normal setting has too soft of a dampening rate, and the stiff setting has sky high dampening rate. So the car pings and pongs between 2 states, neither perfect : normal setting is too soft causing a lot of body roll, and stiff setting is extremely jittery and is preserved only for glass smooth surface.
This is the origin of criticism from some press members of PASM ("we don't like this gimmick, just give us one good setting instead of 2 bad ones"), Porsche engineers admitted this at time of 997.2 release. Sport setting of PASM gen 2 is not nearly as stiff as PASM 1.
PASM is also fixed in Bilstein B16 coilover, either Damptronic or PSS10 version. With the Bilstein Damptronic, the 2 settings of dampening are very close to each other, so close that new users sometimes have a hard time telling if they are different!

So the one line answer is this: when dampening rate is too high, compliance goes down and tire loses contact if road is not perfect, your car "swings", another way of saying losing road contact/control. This is fact, "law of physics," so you cannot alter it, OTOH there are definitely a number of work-around's that you could try. IMHO:
1. Not use the stiff PASM setting when road is imperfect, and tunes the suspension (for example stiffens the suspension with drop links, stiffer tires, etc.) so that there is a good compromise for a majority of your driving. This is your case with Techart springs and I think it can be done successfully, now that I hope you recognize what you are dealing with.
2. Use the stiff setting all the times and softens the tire/other suspension components (not a good solution).
3. Changes the source of the problem, which is the damper/shock absorber, by using a coilover. Bilstein has two choices: non PASM coilover (Bilstein PSS10) or one with improved PASM (Bilstein Damptronic).

Originally Posted by spf4000

Minor correction. Dampening doesn't have an impact on the amount of body roll. The only things that change the amount of body roll are spring rates and anti roll bar stiffness. Stiffer shocks (specifically low speed compression dampening) just slow body roll.

Originally Posted by cannga

Hi thanks for your input. I think I know what you're trying to stress: dampening is a time dependent parameter, that is designed primarily to control the oscillation of the spring. But IMHO yes dampening very much does affect the amount of body roll; we in fact have the very illustration of this in our Turbo. This is how PASM works!

PASM normal and stiff setting: which one has less body roll, the Sport setting or the Normal setting? The Sport setting right? What is the one and only difference between the 2 settings? The dampening rate.

I am not a physics major but I think another way of approaching this issue is assuming 2 extreme positions: dampening rate being zero, and dampening rate approaching infinity. In the case of infinity rate, the car will literally have no body rolll at all.
I think the explanation is in the fact that even though it is, as you said correctly, low speed compression, the low speed parameter itself is not one single value but is in fact variable - there are different "low speeds." Large radius freeway sweep is lower speed than sudden canyon double S curves, both being example of low speed compression. The higher the dampening the lower the "low speed compression" it will affect (I think, anyone please chime in as needed), until at infinity dampening where it does not allow any movement at all. I think I might be confused, and confusing. :-) Interesting discussion and good point.

Originally Posted by kitw

1. Sport or Normal, you will "eventually" roll the same amount. 2. Sport is stiff enough to where in many transient events, you never actually experience the max body roll. But, in a long sweeper, in theory you would end up at the same roll angle - determined by the roll stiffness (springs and sway bars.)