Van

In the snow we got the other day, I got to spend some time playing around with the 996 C4 as I terrorized the neighborhood.

It was the first time I got to feel the PSM first hand, since I got the car in the summer. And I was surprised by a few things - and also wanted peoples' input about the "proper" use.

Now, I know this is the racing forum, so forgive me for NOT wanting to know about "properly" using PSM on the track... But, I'm assuming the people here understand vehicle dynamics a little more than in the individual technical forums.

So, here goes: First I was surprised how "serious" or "intense" the the PSM intervention is - it's about an order of magnitude more obtrusive (and noisy) than ABS or traction control. Second, I was surprised how obvious I could tell which wheel it was braking.

As I was going around corners and turning at intersections, I would get the car drifting (where you'd use a normal counter steer to control the drift) and, of course, the PSM would come on - usually braking the outside front wheel. It seemed obvious because there would be a tremendous pull at the steering wheel in that direction (picture getting a sudden puncture in one front wheel). Maybe it was braking a rear wheel too, but with less tactile feed back, it was hard to tell.

I tended, presumably due to my track experience, to counter steer a little when the PSM started doing its thing - in part to keep the car balance as the outside front wheel "loaded" with the brakes applied, but also to try and "catch" the drift. When I counter steer, I'm changing the steering input angle, and the direction of the car, thus the PSM has to recalculate what it's doing. Because I was playing and intentionally "upsetting" the car, it was hard to tell exactly how much "saving" it was doing - and how much "saving" I was doing.

This brings me to the crux of my question: Is the system designed for this type of "correction feedback" from the driver, or is it designed for a driver that just grips the wheel tightly and keeps it at the same rotation angle while the PSM is PSMing?

Clearly, it's not nearly as "fun" to drive around in the snow with the PSM on, but I imagine it is safer - both as an aid to tell you when you're approaching the limit (like ABS) and also to assist if you become distracted and don't react to a skid/drift fast enough. Does anyone have stories about experiences where the PSM saved them or did harm (either on the street or on the track)? I'm curious to know!

(Sorry for the long post.)

DrJupeman

It isn't always so abrupt. I suspect being in the snow the system felt it needed significant correction RIGHT NOW so made some easily-felt corrections. I suspect in most normal operation you wouldn't find it as intrusive even when it is activated.

Alan Herod

I rode with one driver who got so far behind the car that he completely blew the the turn entering Thunder Valley and got into the marbles before the road drops away. All kinds of racheting noises and PSM corrected the yaw and saved the car.

PSM can be a valuable tool for learning the limits. Wish I had had it on the Boxster, I'm sure it would have cost us a lot less then $14,000.

RJFabCab

Appropriate driver correction with respect to steering input is surely a good thing while PSM is in action.

I tracked rather extensively in a car with PSM. It's not the 'save all', but it sure is one heck of a correction system.

PSM reads multiple sensors and has the ability to brake wheels independently and cut throttle... BUT you still need to steer the car.

I presume that the system is rapidly (or constantly) sampling steering input during dynamic vehicle correction.

I once floored the throttle on a slick road into a left hander and had to near opposite lock steering correct 3 times while the PSM gizmos were doing their thing to control the rear wagging all over the place. It was cutting throttle and braking wheels as I was correcting the steering.

If I didn't provide steering correction, I would have spun. Instead, the car never stopped and I drove off in a straight line.

RJFabCab

PSM is supposed to be a progressive learner.

If you frequently get the car out of control, the system will tighten things up.

Drive for a month with no issues, and the system will give you more rope.

Regardless, PSM is always in the background providing the safety net.

BostonDMD

I have PSM off in the snow....... in my Cayenne S and when the family is not onboard.... much more fun....

When the family is riding with me PSM is always on, for their sake....

Veloce Raptor

Snow?????

morefun

Funny, on the way home from work Thursday PM during the storm, I pulled into the huge empty parking at the local casino and had some fun. The PSM is amazing how it reels the car in. Very impressive technolgy. I couldn't "feel" it working as you describe Van but I found it hard the hang the car out when it was on. When turned off it was easy to drift the car but the inputs had to real fast to keep it under you. Cool stuff! Great learning experience. btw The Quaife TBD in my Cayman really makes it much more fun. I felt like I was 16 again sliding my "bugeye" Sprite around the local shoppiing center (malls wern't invented yet -1969). Anyway I leave my PSM on at the track. I don't see the light flash all that often. The uphill at LRP, at LCMT,the cresting, off camber tight right hander final corner exiting onto the main straight etc.. Yea, I know I'm a ******, but I DE to have fun and I want to drive it home to do it all over again - cheap insurance.

Van

I guess that's 7 years of technology improvements!

924RACR

Tuning varies from car to car and year to year, of course, but stabilizing interventions will almost invariably get stronger when you countersteer vs. simply reducing your steering input on oversteer. This is as much a control theory question as a vehicle dynamics question. But remember, not everybody who buys a car with ESC (PSM) even knows too much about countersteer, or how to drift a car, etc. So the system tuning must be robust to all drivers, even the absolute high school drivers-ed reject. Otherwise it's not safe, and underneath it all, these are all safety systems.

With more practice, and less dramatic and sudden oversteer events, you should be able to get adequate stabilization from the system with only a modest steering input reduction, not a full blown countersteer. Furthermore, having ESC will allow you more time to react and start feeding in countersteer, in those cases when you do need to get all the way to full countersteer. So without ESC, gas it on ice and you need to be instant, almost predictive, with your countersteer; with ESC, on the other hand you will at very least have time to recognize the spin and react, instead of having to predict.

Make sense?

morefun

924RACR

Makes sense for old farts like me!

Van

I understand you, too. I'll have to practice more - and take it to the track sometime to see how it reacts there.

924RACR

Cheers... that's the day job, so it's easy for me to overshoot on the technical complexity and start talking about yaw rates and accelerations, control deviations, gains, error, control factors, slip angles, etc - needed a sanity check!

cviles

As regards to steering the car while PSM is "working": That's how the system knows where the driver wants to go. It doesn't have lasers or cameras or anything like that; the only thing it has to gauge the driver's intentions is the position of the steering wheel. It uses that, and other measurements, to determine where the car should be traveling versus where the car is traveling. After a bunch of math, it decides to cut engine power, apply brakes to specific wheels, etc. to try to get the car going in the direction the wheels are pointed. If you point the wheels at a brick wall, you're going to hit that brick wall. Probably head-on too.

The latest generations of PSM (987/997) are more permissive of slip angles than the older versions. They also allow more aggressive braking before reactivating. If you have the Sport Chrono option you can further increase the slip angles the system allows before cutting in.

I know a lot of people dislike electronic aids on philosophical grounds, but not spending tens of thousands of dollars on repairs and medical bills sure leaves a lot of room in the budget for more seat time.

Patrick E

I used to be one of those people Chris referred to as disliking electronic aids on philosophical grounds, but 996 track usage has changed my opinion. I've found the system's interventions to be rare and pretty subtle (I'm sure it would be more aggressive if you really screwed up) and it certainly does give me additional piece of mind. One negative side-effect is that I find myself occasionally "driving around" the system and not doing things that would otherwise cause the system to intervene (e.g. aggressive trail braking). This would obviously be a problem if you're reaching for those last tenths of lap time improvement or racing, but for me it's a good trade-off in a DE environment versus the potential repairs and medical bills Chris refers to.