Bob Rouleau

Great Story. Should be required reading for all Instructor Candidates!

Best,

MANUAL

My pleasure, Bob.


Actually, Bob, I said no facts were stated to prove OR disprove if PSM would have helped. Facts aside, my personal unsubstantiated belief is PSM would have helped Ben.

In addition, after witnessing Porsche watering down the 997 GT3 clutch-type, asymmetric mechanical LSD from the 996 GT3's 40/60 (40% during acceleration/60% during overrun) locking factor to 28/40 to make way for TC, I believe, though I'm not an auto engineer, it would have been possible to incorporate PSM with the CGT's clutch-type, symmetrical 32/32 LSD. Of all the Porsche GT street cars, the CGT is the only one with a symmetrical LSD and has relatively low locking factors. I am confident that installing PSM on the CGT would have been a walk in the park for Porsche engineers. PSM and a 22/27 LSD was standard on the 40th Anniversary 996. And the exact same PSM and 22/27 LSD is on the current ROW 997 20 mm sports suspension.

With Ben's death and Ferrari including CST on its 430 and 599, I think the time has come for us, purists, to set aside our superbia, be honest with ourselves and the driving mistakes we make on a daily basis, and ask Porsche to offer, either standard or as an option, a switchable TC and switchable PSM on all its future GT cars. After all, if Porsche, by itself, has chosen to water down the GT3 by lowering the LSD locking factor and adding TC, I say please add a bit more water and add PSM for the future so that we may have a better chance of arriving home from the track and/or street alive.

Reference Sources:
http://www.deter.com/porsche/PSM.txt
http://www.pca.org/tech/tech_qa_ques...7240E0FB690%7D
http://www.worldcarfans.com/news.cfm...ml/country/gcf
http://www.worldcarfans.com/news.cfm...3-more-details

MANUAL

Ay caramba! Snell 2000, inertial-reel belts and 135-140 mph?

Please try to have a sit-down dinner with your family before the event for they realize not the risk you lay. Hopefully you'll give us a good report when you return. Godspeed, Mike.

JasonAndreas

I could be misinterpreting what is written in the workshop manuals but the brake control (ABD) portion of traction control (which PSM would rely on) doesn't operate at speeds greater than 100km/hr and Ben was traveling at 2-3 times that speed?

MANUAL

Jason,

Looking at the Service Information 2004 Technik (technical) Introduction (manual for the) Carrera GT, below is the manual's description of the CGT's ABD 5.7:

During acceleration, in the event of the one wheel slipping, that wheel is braked by the ABD unit until stable driving conditions are reattained. The application of brake pressure is achieved by the individual hydraulic valves for each drive wheel, located in the ABS hydraulic unit.

The component functions of the ABD 5.7 are implemented in the overall TC 5.7 system.

Unless I'm mistaken, ABD only works on the drive axle. PSM would need to rely on the non-drive front axle ABS channels as well. With regard to operational speed, the manual says:

the TC function is active at all speeds when acceleration is applied. Since ABD 5.7 is one of three components of TC, I believe ABD is active at all speeds until prolonged TC applications cause the brakes to overheat.

If ABS and TC are active at all speeds, I am confident PSM would not be any different. Please recheck what is written in your workshop manual regarding the 100 kmph. Either we are misinterpreting the manuals or one of them is incorrect.

Bob Rouleau

Manual - thanks for the very informative post on ABS and the various LSD options. It appears that PSM is indeed incompatible with the high percentage locking differential used on the GT2/3 and perhaps the 32/32 of the CGT. Your post informed me that it can be done with a lower percentage of lock.

My hypothesis about the benefit of PSM in Ben's case are based on a test I did with on a wet skid pad. Our local club is fortunate to have access to the government test facility (PMG - google if interested). They have a huge skid pad which allowed me to explore the capabilities of PSM in a 2003 996. While the test was hardly scientific, I was able to put the car into a spin or lurid slide by snapping the steering wheel into the turn. This was on a wet skidpad and I was going around 120 KPH. The sequence was, accelerate to speed, lift and simultaneously crack the wheel hard to the left. Before anyone comments, I agree that no driver in his right mind would do this ..except perhaps in a panic situation.

I came away quite impressed with PSM - I had to brutally swerve to overcome it. This was in the wet (I had no desire to ruin a set of tires). Perhaps in the dry it would have taken more speed to overcome the electronics. Still, applying a brake to one wheel or another can do only so much. Driving more sensibly, PSM protected me from a lot of foolishness and the car was virtually impossible to spin.

Rgds,

Bob Rouleau

Jeff! Why are you sounding like a prosecuting attorney? This thread has been very enlightening (to me at least) and is a polite exchange of ideas and frankly, some guesses. Manual has reasons to believe in the value of PSM. He makes a pretty good case.

I am not a big fan of PSM - although my reasons are a little more abstract.

1) PSM more or less eliminates trail braking to rotate a 911 on sticky tires into a tight turn. Yaw control forcefully kicks your foot off the brake pedal. The effect is less intrusive on street tires and I suspect the software cannot cope with the additional grip of R compounds. In fact, the algorithms are calibrated to Porsche 'N' rated tires.

2) I have observed too many drivers being saved by PSM without being aware of it. They *think* they are driving smoothly. This gives them a false sense of their capabilities and that of their car. Except as described above, PSM does not intrude if the car is properly driven. When it does intervene (again, exception noted) the driver has made a mistake. At DE I have gotten in the habit of looking at the rear rotors of students cars. Drivers who habitually invoke PSM will have more wear on the rears than on the front!

I would be in favor of PSM (with certain other conditions below) if it sounded a clear and very audible warning to alert the driver that it had made corrections.

3) Nick feels that Porsche should fit PSM to its high performance cars. If one goes down this road, the next step will be to attack Porsche for allowing a certain degree of freedom before PSM intervenes.

Some whiner will claim that PSM let the car get out of control and that Porsche is responsible for the accident.

Note, Stability systems fitted to other brands of cars are very fast to intervene - too fast to please a good driver. Mercedes is one example. The "off" switch is a placebo, it does nothing except delay the onset of intervention by a minor amount. I do not want my future sports car hamstrung in this way.

4) So, I would be willing to live with mandatory stability aids providing:

- they sound an audible alarm when in operation
- they can be disabled, and I mean *disabled* by the driver.
- owners of PSM cars are taught the limits of the system to avoid the sort of stupidity which defeated the purpose of ABS on passenger cars.

5) While we're at it, I think buyers of high performance cars should be obliged to sign a no-recourse waiver to avoid future lawsuits designed to deflect blame from the driver.

Best,

MANUAL

No offense taken, Jeff. I am sorry to have laid out my unsubstantiated personal belief. Alas, I yielded to temptation.

However, I have been greatly offended by Bob. His clandestine, hardly scientific PSM-thwarting on a government skidpad has chipped away at my personal PSM belief.

JasonAndreas

The exact wording is, "One-sided wheel spin on the drive axle is further prevented by brake control up to a speed of 100 km/h."

Bob Rouleau

Manual, I am terribly upset that my casual experiments with PSM have offended you. It would be awful if you began to think that the PSM god had feet of clay! How may I remedy this awful situation? Could I perhaps call Dr Phil or Dr Laura on your behalf?D

On LSD versus ABD, as Jason has pointed out, ABD normally operates at relatively low speeds, the original systems I had on my cars were functional below 50 Km/h - they have gotten better but not good enough for cars driven on a race track where cornere exit speeds are often far in excess of 60 MPH.

I also think that applying the brake to the lightly loaded wheel (the inside rear) is less efficient than mechanically diverting the power to the wheel with better traction.

For non track use, a limited slip differential is useful on slippereyt surfaces like snow, it can make the difference between moving or sitting helplessly with one wheel spinning. There are side effects though, a swerve is likely if the driver applies too much power - unless traction control is available and a very intrusive one at that. I can't see a CGT being driven in snow or mud so the question is moot.

Best,

Bob Rouleau

Here's one for Nick. A post on the 993 forum - teen agers manage to crash two supercars. Do they both have Stability Control?

https://rennlist.com/forums/993-forum/264962-ot-enzo-murcielago-17-year-old-driver-mess.html

Ron_H

Icon appears to be correct. Read the whole thread and discover that the Enzo was actually wrecked earlier.

Nick

it also appears the Lambo was a bogus picture as well.

MJones

Interesing to read this long thread, armchair quarterbacking, all the what if's.

The simple fact remains that piloting ANY car at speed is dangerous business, and the majority of us DO NOT have the seat time nor experience to to adequately pilot a car in all the situatons that may arise.
Vision, keeping ones eyes up, looking where you want to go, smooth inputs for steering and throttle, the faster you go the smoother you have to be.

Concentration must be 110% for every moment on track, a fractional moment of lapse can spell disaster.

In my limited track excursions I've witnessed a whole lot of drivers who really have no clue as to the proper way to pilot a car, they just want to go fast.

Then we get to the issue of Waivers:
RELEASE AND WAIVER OF LIABILITY, ASSUMPTION OF RISK AND INDEMNITY AGREEMENT
PLEASE READ CAREFULLY AND UNDERSTAND ALL THE TERMS BEFORE SIGNING.

Do you read them before signing or just sign as a formality?

Why did the FC allow passengers?

Will the waivers be found null?

I supose Ben should have had Cory sign a waiver as a passenger.

MANUAL

JasonAndreas,

Thank you very much for rechecking. From which manual are you quoting?

And do you have any manuals for PSM-equipped cars that state the speed at which PSM is limited?