PSM (not PASM)

Although many threads deal with PASM, I don't believe any have given a good description of the components of PSM and how it works. The Porsche website is noticeably lacking in this regard as well. How does PSM work? Is any type of slip differential involved?

Download this The Cayman Club - Downloads - AfterSales Training - Suspension, Brakes & Alignme and read the sections about PSM. There is a LOT of excellent information! Read chapter 4 in its entirety. It describes many older PSM systems, but it's important to understand those earlier systems to best understand the current system. :cheers:

Some years back, when PSM was introduced, Panarama had a spectacular article that fully explained the operation. Aside from that the literature I have seen since is fairly less comprehensive.

Thank you.

Alot of information there and I'm not capable of digesting all of it, however, it seems the autiomatic brake differential is a form of LSD. NO?

No. LSD's point is to ensure that you retain traction. With the differential you have now, you can get wheel spin (loss of traction) coming out of hard right turns, as the inside wheel can't handle all the load. If the outside wheel is also used for "drive" then this loss is minimized to the maximum possible. What PSM does is to apply the brake to avoid loss of control, by correcting steering. And while is isn't the same, it may have a similar effect. Some folks have reported better track times with PSM on than with it off. But, I haven't heard of anyone reporting PSM being better than an LSD.

Thank you, fmarshall. Would you say then that PSM obviates the need for LSD if the vehicle is used for daily driving only?

I actually thought the exact same thing. It made me thinking, if that's an LSD imitation, then it must be a real blast driving an LSD equipped car!

Not at all. IMO a Quaife ATB/LSD is highly beneficial for street driving. Since new, my '06 CS has been 90-95% year 'round daily driver and 5-10% track car in advanced/instructor groups. Wheelspin on the track has not been a major issue. However, getting up hills/driveways in the snow (even with my winter tires) has. PSM/TC helped, but not much, and certainly not enough. I recently installed a Quaife & it's made a huge difference in improved handling, stability and driveability in wet/slippery conditions. I can easily drive up hills/driveways that were impossible before the Quaife. There's a noticeable improvement in the rain. If you'd like a more stable, sure footed car, you'd like a Quaife/LSD. PSM is designed to (hopefully) save you after you're in trouble, while ATB/LSD will keep you from getting into trouble. Although having PSM is comforting to have, I don't ever rely on it to save me. I generally turn it off for the track. Even if I could, I can't think of a circumstance I'd turn off the Quaife.

I really don't like the fact that the car thinks and reacts for me now that I've had it for a couple of months. I know when the rear will go out and when it will stay put (i.e., I know how much throttle I'm using). Yesterday, after watching the PSM light trigger as I went around a corner and slowign me down at the same time, I tried the PSM in off. I really like the extra control I can give the car. So, is there a way to reverse the way the switch works--when you start the car, PSM is off, and when you push the button, PSM is on?

It would seem to be pretty easy to reach over and push a button. Forgetting to do so, for those folks that need PSM on, wouldn't be safe from Porsche's point of view, IMO.

It is, but, I really don't like the big yellow light. I would rather turn it on when I wanted and leave it off the majority of the time.

I was playing with my car a bit. I stopped with one rear wheel on asphalt, and one on dirt. (Well, dirt covered asphalt.) And then turned off PSM and proceeded with a burnout. PSM (or ASR) kicked in anyway. Light was flashing on the dash, and the car accelerated more or less without fish tailing. From manual: One-sided spinning of the wheels is reduced, even with PSM switched off, to enable optimum traction on all drive wheels. Wonder how this would work with ATB fitted. I guess more testing later.

Probably when speeding on a controlled environment that might apply, but when you are on an non fully controlled environment PSM is by far the best addition to the new Porsches (and cars in general) The previous weekend I went to my local track to do some speed tests, (its a 10km twisty track) and in a corner with good visibility I wanted to test how the car handles when going at full acceleration, not during the corner, but accelerating in the staright and entering the corner with the pedal pressed to mantain the acceleration during it, I entered the corner at 150kph and mantained the acceleration over the complete turn, but just after the middle of it the tail started to drift (the tires were not warm enough) for me it was a totally different feeling with the mid engine car, it was as if the pivot it is on the middle of the car (I am very used to controlling front engine rear wheel drive cars on corners, even when drifting), I just lifted the pedal to move the weight distribution to the front and induce oversteer, but the car already was in a spin, I was looking directly at the side of the road (there is a lake there) the car was transversely on the road, and with a tight corner right next, to the opossite side, where there is a big wall on a side and the mountain on the other. I was only thinking about how to stop the car the in the most safely possible way but suddenly the yellow dash light come on and in less than a second, with a very abrupt intervention of the PSM the car is on the correct line again, totally controlled, in the entrance of the next corner, ready to push the throttle again There is no way that any human can control a car better than a computer (just think that in a second the car computer can know 1 million times how much the flywheel has moved), what a human can do is to avoid the dangerous situtations, but by far the computer can handle them better than anything (similar as why today the most advanced combat airplanes can't fly without the electronic system that stabilizes them)

So I want to have a body kit that makes my car as ugly as a stealth fighter. That way I can drive as fast as I want without being caught by radar!!

Great story! I'll just do what a fighter pilot told me to do--put tape over it.

I had a recent experience with PSM while driving up a steep snow covered hill. The car ahead of me slowed to the point that I was forced to stop. When I tried to start again the tires slipped and the PSM kicked in and reduced the throttle response to almost nothing. My foot was on the floor and the car was barely moving forward. Of course there were cars behind me so I let the car work out thing for itself rather than experiment. A couple of questions occurred to me: 1. Would letting off the gas and then stepping on it again change the way it was behaving? Sort of like pumping the gas pedal. I tried this later on an open hill and it seamed to help some but I'm still not sure. 2. What would have happened if I reached down and turned off PSM during this? Would the engine have imediately gone to full throttle sine I had the pedal to the floor? In this condition I would have preferred the LSD in my previous 944T to the PSM. In the same condition I could have applied gas and the snow tires would have cleared the snow out of the way. Anyone have thoughts on how to deal with this the next time (hopefully next winter)?

Was PSM standard on all 2006-2008 CSs? From my thread search and car manual reading I would assume so, want to confirm. Thank you.

I believe so. Mine has it and mine is a fairly basic CS.

Hello, just one question about PSM. I have a 09 Boxster S with manual tranny and no LSD. If I turn PSM off and I drive hard, full throttle exting a corner, the traction contro light flashes and it seems the PSM interven (it corrected an oversteer). WHY? And there is a way to fully disable it? In my old BMW I could fully disable that.

Hmmm, that's strange. I've had instances when traction control intervened to prevent a full burnout of sorts, but I've never had it correct an oversteer (or an understeer for that matter) while off. I can even get wheel spin between 1st-2nd (with tip on sport) when PSM is off!

The traction control light in the midle of the dashboard flashes so the PSM might be working in someway/ somewhere, isn't it? I'd like to be fully fully fully off but I think I bought the wrong car...

A member here disabled the PSM completely by disabling or removing the yaw sensor somehow. Maybe a search would help!

I cannot find anything about that... can somebody help me?

Let me say first that disabling PSM is extremely dangerous, and "might" void a warranty / insurance claim if an accident is caused due to its absence. Also I must point out that in most ways to disable PSM, you lose ABS too. Not a side effect I'm willing to risk! Oh and one more note, I'm no Walter Rohl, but what I hear from experts and what I read on this forum (from experts also) indicates that with the exception of very tight hairpins PSM will not kick in unless you are not smooth enough in your corners, think of it as a free instructor. Having said that, here are some links if you absolutely insist: http://www.planet-9.com/cayman-boxster-competition/19116-brake-issues-track-4.html#post218521 http://www.planet-9.com/cayman-boxster-competition/19116-brake-issues-track-12.html#post368120