Tell me how PSM works...or not
02-22-2006, 09:21 AM
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Tell me how PSM works...or not
trying to learn the Porsche way of things coming from BMW.
I heard that the PSM cannot be fully turned off. That is that at the track/autox it will turn itself back on in a "hand of god" sort of way.
Seemed like the 996 Turbo drivers were complaining about this a bit.
Then I read that on the 997 and Cayman this has been changed somewhat. From reading the sales brochure I see that a turned off PCM would only step back in under heavy unstable braking.
How is this different than the previous version if at all.
Also, I own and Audi S6 that has a nasty programming where if you are on the brakes and the gas at the same time the engine power is cut untill the gas returns to the full up position effectivelly making lfb impossible. Didn't 996 do the same? is that still the case
Thank you for your patience!
I heard that the PSM cannot be fully turned off. That is that at the track/autox it will turn itself back on in a "hand of god" sort of way.
Seemed like the 996 Turbo drivers were complaining about this a bit.
Then I read that on the 997 and Cayman this has been changed somewhat. From reading the sales brochure I see that a turned off PCM would only step back in under heavy unstable braking.
How is this different than the previous version if at all.
Also, I own and Audi S6 that has a nasty programming where if you are on the brakes and the gas at the same time the engine power is cut untill the gas returns to the full up position effectivelly making lfb impossible. Didn't 996 do the same? is that still the case
Thank you for your patience!
02-22-2006, 10:58 AM
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dont know about 996, but on GT3's you can't left foot brake, if both brk and throttle are depressed, throttle will be cut out automatically. do a search under MDS as poster, he has a get around on that one.
this situation is same with cayman as well.
i dont have psm in any of my 996's. but psm on cayman can be turned off. i have gone sideways and the only time psm will come back on (for me so far) is if you hit the brakes while the rear end is out. else psm is off. (now, this is not a technical advice, but simply what i experienced on track).
i was told you can "kill" the psm but pulling some fuse. i dont know how to do it and dont plan to do it either. but i KNOW, you can completely kill it off this way.
this situation is same with cayman as well.
i dont have psm in any of my 996's. but psm on cayman can be turned off. i have gone sideways and the only time psm will come back on (for me so far) is if you hit the brakes while the rear end is out. else psm is off. (now, this is not a technical advice, but simply what i experienced on track).
i was told you can "kill" the psm but pulling some fuse. i dont know how to do it and dont plan to do it either. but i KNOW, you can completely kill it off this way.
02-22-2006, 12:31 PM
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The Cayman owner's manual describes 3 settings or interventions of PSM. The most sensitive (earliest onset) is with Sport Mode (PASM/Sport Chrono) turned off, or absent. In Sport Mode the onset of PSM is set back to allow some sliding, as long as it seems to the sensors to be under control. With PSM turned off, PSM is set back even farther, but will still be inacted if the sensors think you're in deep doodoo. Moody's actual experience (reported above), however, was that PSM only came on when he touched the brakes with the rear end out.
02-22-2006, 12:46 PM
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Originally Posted by Jim Michaels
The Cayman owner's manual describes 3 settings or interventions of PSM. The most sensitive (earliest onset) is with Sport Mode (PASM/Sport Chrono) turned off, or absent. In Sport Mode the onset of PSM is set back to allow some sliding, as long as it seems to the sensors to be under control. With PSM turned off, PSM is set back even farther, but will still be inacted if the sensors think you're in deep doodoo. Moody's actual experience (reported above), however, was that PSM only came on when he touched the brakes with the rear end out.
the lit mentions front wheel ABS activation as the trigger for the turned off PSM to decide to intervene...but if it comes on with the car getting a little loose that's not too cool for track/autox
02-22-2006, 01:16 PM
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Yes, my understanding is that if you turn off PSM, it will come on only if you are sideways and hit the brakes hard. Basically, it's supposed to make sure that when you decide to bail using the "when in a spin, both feet in" rule, it's there to make sure that emergency stop manuvere is as safe as possible.
It will not come on just because you get it loose
It will not come on just because you get it loose
02-22-2006, 06:07 PM
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Originally Posted by pstoppani
Yes, my understanding is that if you turn off PSM, it will come on only if you are sideways and hit the brakes hard. Basically, it's supposed to make sure that when you decide to bail using the "when in a spin, both feet in" rule, it's there to make sure that emergency stop manuvere is as safe as possible.
It will not come on just because you get it loose
It will not come on just because you get it loose
In any case...thanks for the posts
02-22-2006, 07:39 PM
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PSM 101
PSM is composed of multiple sub systems.
- E gas
- Stability management
- Traction Control
-Yaw control
E-Gas is throttle by wire and all Porsches since 2000 have it. Without E Gas, PSM would not be possible.
Stability Management - uses inertial sensors steering wheel position sensors, ABS wheel speed sensors as inputs. It will detect excessive tire slip angles and take appropriate action by reducing power (E-GAS) and or braking one or more wheels to correct excessive under or oversteer.
Traction Control uses wheel sensors and yaw sensors and will reduce power to prevent power induced oversteer.
Yaw control uses the same sensors to detect excessive slip angles and will take corrective action by reducing braking force (it kicks your foot off the pedal in fact) and braking one or more wheels to correct the excessive slip angle. YAW CONTROL CANNOT BE TURNED OFF. You will feel yaw control kick in if you trail brake or as others have posted, braking while turning to the point that the car gets out of shape. I repeat it is independent of the PSM switch and is always on. This makes some people think that PSM comes back on under braking. That's not true.
PSM can be turned off. Doing so, eliminates traction control - yes you can do a burn out or even a smokey drift and stability management. It will come back on if the ABS is invoked. PSM will go back off after it has made the needed corrections.
E-Gas is always present and if it senses brake application while the throttle is pressed it will reduce engine power to idle. That's a safety measure to prevent a run-away engine. Note, that if you are on the brakes and then apply throttle, the engine will not be cut. This is useful for drying your brakes after washing your car, or for the very deft, left foot braking.
In sum, if you suffer from PSM intervening, your driving is suspect. In my experience the only time PSM can be a nuisance is when trail braking a car on R compound tires. The system is designed around the street tires approved by Porsche (N spec). R compounds with greater traction will fool the yaw sensor into invoking yaw control when in fact the car is not out of shape.
Hope this helps.
Rgds,
PSM is composed of multiple sub systems.
- E gas
- Stability management
- Traction Control
-Yaw control
E-Gas is throttle by wire and all Porsches since 2000 have it. Without E Gas, PSM would not be possible.
Stability Management - uses inertial sensors steering wheel position sensors, ABS wheel speed sensors as inputs. It will detect excessive tire slip angles and take appropriate action by reducing power (E-GAS) and or braking one or more wheels to correct excessive under or oversteer.
Traction Control uses wheel sensors and yaw sensors and will reduce power to prevent power induced oversteer.
Yaw control uses the same sensors to detect excessive slip angles and will take corrective action by reducing braking force (it kicks your foot off the pedal in fact) and braking one or more wheels to correct the excessive slip angle. YAW CONTROL CANNOT BE TURNED OFF. You will feel yaw control kick in if you trail brake or as others have posted, braking while turning to the point that the car gets out of shape. I repeat it is independent of the PSM switch and is always on. This makes some people think that PSM comes back on under braking. That's not true.
PSM can be turned off. Doing so, eliminates traction control - yes you can do a burn out or even a smokey drift and stability management. It will come back on if the ABS is invoked. PSM will go back off after it has made the needed corrections.
E-Gas is always present and if it senses brake application while the throttle is pressed it will reduce engine power to idle. That's a safety measure to prevent a run-away engine. Note, that if you are on the brakes and then apply throttle, the engine will not be cut. This is useful for drying your brakes after washing your car, or for the very deft, left foot braking.
In sum, if you suffer from PSM intervening, your driving is suspect. In my experience the only time PSM can be a nuisance is when trail braking a car on R compound tires. The system is designed around the street tires approved by Porsche (N spec). R compounds with greater traction will fool the yaw sensor into invoking yaw control when in fact the car is not out of shape.
Hope this helps.
Rgds,
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02-22-2006, 07:48 PM
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AC,
In theory what has been described above is correct.
In practice, what I experienced is the following:
With PSM in sport:
It will allow you to get tail happy only in an efficient way. Once you step the tail out more than for just the initial corner exit bite, it will grab agressively the front outside brake (just like BMW's DSC but "smarter") making the car 4wheel drift but point in the direction of travel. It does allow you to keep a cornering arc. Just for kicks I tried it in the wet on U-turns, and it makes you complete the turn, just in a wider arc if you keep your right foot in ("idiot-proof")
With PSM off
I never felt any intrussion whatsoever in rear end out action. Can keep very long rear end drifts and powerslides. Have tried it in the dry, rain and ice and never felt any interference or "safety-net" threshold other than the action of the ABD (rear brake acting as substitute of LSD). It feels like an LSD car but it just feels that some forward thrust power is being consummed while you force the "faux" differential lock. Only nuissance is the permanent flickering of the PSM light.
Haven't been able to test the safety net of forcing the ABS while being out of shape. The few times I have dabbed the brakes while oversteering it just felt it did what I intend it to do. Nothing more.... I guess you really have to be in a "both feet in" situation to test the system. Neither have I felt any stability / directional correction when forcing engagement of the ABS while braking over ice.
You CAN left foot brake, and the system does allow you to overlap brake and throttle for a short period of time (my guess is 1.5secs aprox), but once you exceeed that you loose all throttle and only get it back when you fully release the brake.
Next week when I'm back you can test it yourself
In theory what has been described above is correct.
In practice, what I experienced is the following:
With PSM in sport:
It will allow you to get tail happy only in an efficient way. Once you step the tail out more than for just the initial corner exit bite, it will grab agressively the front outside brake (just like BMW's DSC but "smarter") making the car 4wheel drift but point in the direction of travel. It does allow you to keep a cornering arc. Just for kicks I tried it in the wet on U-turns, and it makes you complete the turn, just in a wider arc if you keep your right foot in ("idiot-proof")
With PSM off
I never felt any intrussion whatsoever in rear end out action. Can keep very long rear end drifts and powerslides. Have tried it in the dry, rain and ice and never felt any interference or "safety-net" threshold other than the action of the ABD (rear brake acting as substitute of LSD). It feels like an LSD car but it just feels that some forward thrust power is being consummed while you force the "faux" differential lock. Only nuissance is the permanent flickering of the PSM light.
Haven't been able to test the safety net of forcing the ABS while being out of shape. The few times I have dabbed the brakes while oversteering it just felt it did what I intend it to do. Nothing more.... I guess you really have to be in a "both feet in" situation to test the system. Neither have I felt any stability / directional correction when forcing engagement of the ABS while braking over ice.
You CAN left foot brake, and the system does allow you to overlap brake and throttle for a short period of time (my guess is 1.5secs aprox), but once you exceeed that you loose all throttle and only get it back when you fully release the brake.
Next week when I'm back you can test it yourself
02-22-2006, 11:22 PM
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Bob: Thanks. That was very helpful. Can one spin the car with PSM off or not?
I inadvertantly tested PSM in Sport Mode and it worked fine. In fact, the car is a better driver than I am. There's a place near me called Mountain Lake that closes during the winter (now I know why). Access is by 7 miles of uphill curves. At the bottom I punched Sport Mode and the Sport Chrono clock and started up. There was no traffic, but as I came around a right-hander into a shaded area about 1 mile from the top I saw an all white road. About the same time that my jaw hit it's bottom most position, the rear end tried to pass the front. I had hardly begun my usual frantic steering corrections before PSM stepped in and straightened the car out in about one second. The road was white and slippery most of the remaining way to the crest (the only place safe to turn around), but the car made it all the way with only a few minor PSM interventions. I'm a believer now.
I inadvertantly tested PSM in Sport Mode and it worked fine. In fact, the car is a better driver than I am. There's a place near me called Mountain Lake that closes during the winter (now I know why). Access is by 7 miles of uphill curves. At the bottom I punched Sport Mode and the Sport Chrono clock and started up. There was no traffic, but as I came around a right-hander into a shaded area about 1 mile from the top I saw an all white road. About the same time that my jaw hit it's bottom most position, the rear end tried to pass the front. I had hardly begun my usual frantic steering corrections before PSM stepped in and straightened the car out in about one second. The road was white and slippery most of the remaining way to the crest (the only place safe to turn around), but the car made it all the way with only a few minor PSM interventions. I'm a believer now.
Last edited by Jim Michaels; 02-22-2006 at 11:47 PM. Reason: addition
02-22-2006, 11:56 PM
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You can spin the car with the PSM off. I've done it with my 05 987S twice dry and three times wet. Both dry spins were lifting off at about 60 mph during AX. The spins in the wet were the same, too much speed in entry and lifting off or feeding in too much steering to correct understeer/badline. You can go around a complete 360 without the PSM.
Haven't been able to spin with the PSM on in "normal" or "sport" setting on the sport chrono. Unless you get both front tires in the ABS range the PSM doesn't doesn't come back on after switching it "off".
All these spins were during AX on a runway with adequate runoff, I would never turn it completely off on the street.
All spins were entirely due to driver error not the car.
My two bits
Haven't been able to spin with the PSM on in "normal" or "sport" setting on the sport chrono. Unless you get both front tires in the ABS range the PSM doesn't doesn't come back on after switching it "off".
All these spins were during AX on a runway with adequate runoff, I would never turn it completely off on the street.
All spins were entirely due to driver error not the car.
My two bits
02-23-2006, 01:37 AM
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Jim - yes you can spin with PSM on. electronics and differential braking cannot overcome physics. Come into a corner too hot and PSM will try to help but, it cannot overcome everything. There is a saying in racing, pros spin on corner entry and amateurs spin on corner exit (right foot too hard on the pedal).
Rgds,
Rgds,
02-23-2006, 09:38 AM
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Originally Posted by Bob Rouleau
Jim - yes you can spin with PSM on. electronics and differential braking cannot overcome physics. Come into a corner too hot and PSM will try to help but, it cannot overcome everything. There is a saying in racing, pros spin on corner entry and amateurs spin on corner exit (right foot too hard on the pedal).
Rgds,
Rgds,
CG, yes please!
02-23-2006, 09:52 AM
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Originally Posted by AC coupe
Bob, thanks for the primer
CG, yes please!
CG, yes please!
)Just let me know to give warning to the housekeeper...
02-23-2006, 01:47 PM
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Bob, excellent summary...
FYI, the key difference between PSM & most others (incl. BMW's system) is allowed slip angle. PSM ver 1 allowed 5 ~ 7 degrees slip (don't forget - the yaw sensor data is combined w/the steering angle sensor) angle. Ver 2 (PASM/Sport) can run up to almost 9 degrees (that's quite a bit for street tires). It's quite a system, and while I've met many folks who claim to be "better" than PSM, the reality is that they are not.
JS
FYI, the key difference between PSM & most others (incl. BMW's system) is allowed slip angle. PSM ver 1 allowed 5 ~ 7 degrees slip (don't forget - the yaw sensor data is combined w/the steering angle sensor) angle. Ver 2 (PASM/Sport) can run up to almost 9 degrees (that's quite a bit for street tires). It's quite a system, and while I've met many folks who claim to be "better" than PSM, the reality is that they are not.
JS
02-23-2006, 02:16 PM
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JeffES - thanks for the update. I was aware of the ~7 degree max slip angle, it's one of the tests Porsche does on the N rated tires. I agree the 9 degrees is a lot, a street tire should be sliding by then since most of them have a max slip angle around 7 degrees as far as I know. Then again tire technology changes rapidly and perhaps slip angles have been increased.
I fully agree that PSM does not hinder a good driver operating within limits suitable for DE other than the previously noted yaw control which intervenes while trail braking on R compounds. Under hard racing conditions, I think a competent driver would be faster without the electronics. From my observation as an instructor, most of the people who complain about PSM would have lost control without it.
Is Ver2 on the 997 or some earlier models as well? The CST system on the Ferrari 430 (their version of PSM) allows a lot of lattitude before intervening. I could get the tail of the car seriously sideways in spite of traction control and stability management with the mannetino set to 'race' mode. It seems to scale with the setting and goes from nanny (poor traction mode) to 'yee-haaa!' in race mode. Nicely done I thought.
Regards,
I fully agree that PSM does not hinder a good driver operating within limits suitable for DE other than the previously noted yaw control which intervenes while trail braking on R compounds. Under hard racing conditions, I think a competent driver would be faster without the electronics. From my observation as an instructor, most of the people who complain about PSM would have lost control without it.
Is Ver2 on the 997 or some earlier models as well? The CST system on the Ferrari 430 (their version of PSM) allows a lot of lattitude before intervening. I could get the tail of the car seriously sideways in spite of traction control and stability management with the mannetino set to 'race' mode. It seems to scale with the setting and goes from nanny (poor traction mode) to 'yee-haaa!' in race mode. Nicely done I thought.
Regards,