Hmmm. I've had several cars with various forms of traction control. In track events and autocrosses I've always been about 2 seconds a lap quicker with it OFF.

As a result, I generally drive the 996TT with PSM off even in town, on the highway, etc.. That said, I have played with it on a few times and it is quite good compared to other systems. It actually allows you to have some fun, whereas many systems (such as the one on the e36 M3 and Z06 Vette) are far too intrusive. Still, the butt-o-meter says a good driver will be significantly quicker with it off.

-Donn

 

Bah... just disconnect the front drive shaft and go into GT2 mode... Sideshows.

 

Ummmm... wrong....

If it is off... it stays off until the computer detects various conditions such as high lateral loads, quick brake application and others... and it turns itself back on.

I am using the factory service manuals for reference.


Kind Regards,

Joe West

 

I've done most of my best handling-oriented driving with the
PSM switched off. You really must try it that way if you haven't.
The car becomes a much more willing and intuitive 'partner in
crime'. During at-the-limit driving, the PSM can interrupt like a
lawyer during sex. As PorschePHD says, it will shut down power
for a full second or so if it thinks you're doing something stupid,
and in most circumstances it's right, but there are cases in
tight switchbacks, where you want it to swing hard from maximum
tail-out one way to max tail-out the other way, and PSM imposes
a 'cooling off period' which feels like a senior moment at just the
wrong time (for speed).

Uppity statement:

If you haven't driven your 996tt in such a way to have triggered
PSM hard enough to have noticed it, and maybe even become
impatient with it, you haven't really pushed the limits with your
car, handling-wise. Note that on a typical race track, you shouldn't
really push the limit. The speeds are too high, and even if there is
runoff room, it's typically gravel or dirt meant to stop a car, and
it's yucky to overbake it into that stuff. Most tracks don't even
have any changes in direction that are sharp enough to model
something like a lane-change-at-sixty-to-avoid-a-deer that would
challenge the transient handling characteristics of the car. This
sort of handling *does* occur occasiionally during *races* due to
traffic, but it's not a part of the track itself. At street speeds,
however, the cost (in distance off-line) when you overdo it, is less,
and often it's on relatively safe asphalt (if there's no traffic!).
All in all, I believe that autocross is the very best way to
really explore the limits of your car's handling. It doesn't stress
the car, and if you go over the limit, you just slide and maybe
spin in a safe flat place. The whole art is to jump right to the limit
*right now*, and hold it there for a full minute. Nowhere else can
you reliably safely do that.

On the other hand, I usually always *drive* with PSM. There
was a time when I had to get from A to B fast during a heavy
rain, and happened to be using tires that has so litle tread that
they were essentially slicks. On the freeway with standing water
at 80mph the PSM was ticking on and off like a geiger counter,
and few other cars could have done as well to make that drive
possible.
Joe

 

Joe... I'm shocked and dismayed. I thought that WAS what race tracks were for. I must have been doing it wrong this past seven years!

OK. I'm just yanking your chain. I get what you are saying. If you haven't pushed the handling limit before, don't do it on the race track first. Do it on an autocross course first... which is a safer environment and speeds are lower.

OTOH, for a driver with experience, the only reasonably safe place to push both the handling and acceleration limit is on a race track.

 

I thought it was like the normal procedure when you get in the car, put seat belt on (check), Glasses (check) PSM button off as not to jar my head (check)

 

So we agree that:

1 - If you haven't actually *raced* in some form, autocross or
road course etc, you probably haven't really pressed the limits
of your car's handling. Not even insane antisocial suicidal street
driving can really get you to what the car can do.

2 - If you want to explore the real limits of your car, autocross
will do it, and do autocross first. It is safe. Even DE events won't
get you to the limits. You may go at 8.5-9/10ths by the end of
the day at a DE/track day, but the limits are at 9.5/10ths to
10/10ths, and the difference in car behavior and experience at
9/10ths and 10/10ths is huge. Also, it's good to experience the
car at 10.1/10ths (losing it) enough times to know where it is,
how you get there, and to know intimately how to catch it and
prevent it. You can't be sure you really know the limit if you
haven't gone over it, and not just once a year ago.

I think you and I are actually 95% in agreement, but that's no
fun so I'll nitpick the remainder: No matter how experienced
you are, you can push the acceleration and handling completely
in autocross. The only extra things that you can press on road
courses are the *speed* limit of the car, and the difference in
high speed handling due to aerodynamic effects at that speed.
You also get to press the danger limit higher, though not as much
as pushing on the street . The car accelerates harder in first
and second gear than in third or fourth etc.
Joe

 

What I'd like is a ring or button like the WRC cars, but instead
of it being a gear-changer, I'd like it to turn on PSM for just as
long as the ring was pulled, or button was pushed. That way
I could overbake it at will as long as I knew what I was doing,
but I could engage PSM for just as long as I needed if I found
my rear tires had gone away at just the wrong place...
Joe

 

My car is used for autocross only. I've messed up two runs this year by accidently leaving the PSM on.
Has anyone autocrossed with the front drive shaft disconnected?

 

Actually, I think we are in 100% agreement.

 

Well put Joe!
I don't have enough self control to drive mine on the street and I don't have enough experience to road race....... so autocross it is

 

Joe and Racer63:

I agree with the general concepts completely, sadly, I have not tracked my tt because it isn't broken in yet. I will comment on the effects of PSM then.

Supposedly, the PSM system will allow a 7 degree slip angle (I think) before intervention. Unless something is wrong or your using uncommon tires, this is pretty much the maximum optimum slip angle. So, PSM doesn't get involved unless you are doing something uncommon or .. you made a mistake.

See this link for the most technical article I have been able to find.
http://webdisk.berkeley.edu/~dlrowney/PSM.txt

What I am hoping is that I can drive the car and see when PSM intercedes. I can then match it with my data acquisition system and see if I made the error or if PSM was too safe.

 

My thoughts on PSM...

I picked up my car and went on a 3,000 road trip with some buddies in Southern Oregon and Northern California. Basically this is an annual trip to the Monterey Historics from Seattle.

Almost all of the entire first day of high speed back road work (out of Grants Pass Oregon) I left the PSM on. I could not believe how unstable the car was. Things like getting twitchy when I might just touch the centerline paint stripe in the middle of a corner in hot and dry conditions, or other seemingly unexplainable and unpredictable instability in the middle of a high speed corner. Finally out of total frustration with how the car was driving I turned off the PSM and the car was transformed...in the most positive of ways!! I cannot believe they actually call it a stability management system...I think they should call it instability management. I think in the end it is basically a legal liability enhancer for Porsche.

So it is off all the time now :-))

John

 

Yes, under certain circumstances, I can use a bigger-than-7-
degrees slip angle in the rear, if only for an instant or so, and
PSM's killing the power for a full second at that time is not helpful
to my purposes.

Coolness! Tell us what sort of data acquisition system you have!
Joe

 

Joe:

I am investigating the best approach to data acquisition for my tt now. The debate is how much can I get off the ECU and PSM, and how much I will have to get myself. I will probably go with an AimSport system as they do an excellent job (Pi or Stack level) for about 1/4 the cost, or less.

I will keep everyone updated as to my progress.