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PSM question for the technical porsche insider guys

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I have a question about PSM

I understand there are two aspects of the PSM. One is for stability (YAW) and the other is for traction.

How is traction defined? How does it relate to the LSD function of the car?

I understand that when the PSM switch is turned off, that once the brake pedal is pressed whiles its "safety zone" is being exceeded it automatically turns it's self back on.

Does the LSD function continue to operate while the PSM is in the off mode? I.E. will it continue to apply braking to the spinning wheel in-order to transfer power to the wheel with more traction? How much braking force will it apply attempting to get traction? If both the wheels don't ever get traction will it allow me a smoky burnout or will it eventually apply brakes until the car starts moving forward without wheel spin?

My question arises from this. In my other cars with a torsen sensing LSD, I could charge into a corner and use the gas to "step out" the back end, inducing oversteer to get me through the corner. The LSD made sure that both wheels kept going. (not doing the one legged chicken scratch). With the 996 with PSM on of course it limits the amount of sliding, hits the brakes and flashes the little orange light at me. Now if I turn off PSM, will it allow me to get the sliding/wheel spin in the corner but STILL modulate the left/right rear brakes to assure that both wheels are spinning and trying to get the power down? OR will I just get that chicken scratching going?

Porsche of course doesn't publish such detailed data on how the PSM works. I just don't see it as a good replacement for a LSD.



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Hey Andy,

this post was over a year ago, but here is the information I think you are looking for. You may already know this.

What you are referring to as LSD "limited slip differential" may also be confused with "ABD" automatic braking differential.

According to some of my very early 911/Boxster Porsche brochures and my own experience with Boxsters "ABD" automatic braking differential

this is how it works in a nutshell.

PSM Porsche stability Management while ON uses ABS, anti-slip regulation, an automatic brake differential and a battery of sensors

that monitors direction, pitch, speed, yaw velocity, and lateral acceleration. It will apply the brakes to individual wheels in order

to stabilize the vehicle based on what kind of slide/skid the car is in.

Included in PSM is the ASR anti slip regulator, and ABD. If one tire slips the automatic brake differential applies the brake to

the slipping tire, hence reacting and behaving just like a limited slip differential. If BOTH tires spin, then the ASR slip regulator

kicks in and retards the ignition and cuts power so that traction is regained.

Turning PSM OFF will disable the ASR, four corner braking montiors, and pitch/yaw sensors...... BUT the Automatic braking differential stays on at ALL times

up to 62 mph... That is why you will notice that even with the PSM OFF light showing you will still see a separate flashing warning light letting

you know that ABD is still kicking in during certain rear traction sliding situations to try and behave like a limited slip differential....

Hope this makes sense. It is pretty amazing programing that Porsche has developed. But nice to know you can turn it off if you are brave enough ;^)

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