chuck911

Gary, I'm so jealous of you, living down there with so many thousands of miles of really superb roads all around. And dealers happy to have you drive them in their brand new Porsches. But mostly the roads. Best drive I ever made, 101 and Highway 1 all the way down the coast, over Mt Tam to the Golden Gate. Can hardly imagine how you must enjoy having roads like that so close by. And the Carrera. In this case mostly the Carrera. Thanks for taking time out from driving the roads of southern Valhalla to do this outstanding write-up. Your comments about the C2 vs C4 are very similar to my impressions comparing the 997.2 C2S with a Carrera GTS.

simsgw

Sorry I overlooked this question: regular PASM so far as I could determine. That is, I checked the Monroney sheet for each car. If I were younger, or not so lazy, I'd have been more thorough, but... well, I'm not either one.

Gary

jmct

Thanks for the write up Gary, very informative!

Hammer911

Hey!...I resemble that remark!

cksuen

Thanks, Gary for the response!

Looks like I need to try out a PDCC car some day. :-)

lawrence

SiNi

Gary, thanks for such an informative review!

You have made a major contribution to the PDCC debate! I thought you would like it!

Rainier_991

Gary,
your're going to do bad things to me one day...

Like you I'm an aerospace engineer (avionics) so I have a similar mental illness (that comes with the job I suppose)

"FLICK/CATCH/CORRECT"

That intrigued me no end. So much so that I had to take mine out for a spin and try it out.
I think I will not report on this as I think any comparison has to be done by the same person or else it is meaningless. You are that person.
So, please add a C2S, Sport Chrono, SPASM, no PDCC to your growing list of things to do.
Just kidding (sort of anyway)...

Rainier

simsgw

Clearly, you were right. And a couple of points I should put down for the record.

• Tire Pressure. I was not able to properly set all the cars to the correct pressures, though I agree with... Rainier was it? who said that effect is noticeable and must be considered. The Pannie and my own C2S were correct of course, but not the two short term loans, the two C4S examples. Just not practical to adjust the pressures, but I did check them and I am fairly confident I can separate the effects of the overly high pressures dealer mechanics always seem to set.
• Steering. It was implicit in my report, but to be explicit about it: I noticed no difference in the steering itself between my C2S and the two C4S examples. The feel through the steering wheel is different because the vehicle dynamics are different, but the steering system feels the same. I concede they may have to use different control maps on the steering to make both models feel the appropriate way they do, but if so it is not evident (and should not be if done correctly). I felt nothing that I would attribute to any other cause except the chassis differences I was evaluating.

This always gets tricky because it's a semantic issue more than it is technical. When does the feel of a car through the steering wheel become the steering feel of that car? Unquestionably, chassis set-up changes that feel-through-the-wheel whatever we name it, so yes the C2S and the C4S feel different.

For my earlier report, I took the position that we were interested in the chassis options and the overall feel they achieve. For this earlier question that we discussed, the best I can say is that no changes to the steering system were detectable for me.

Gary

Rainier_991

I'd like to use our new term "squishy". It does a brilliant job of describing the effect of tire pressure. Tire pressure adjusts the "squishiness" of the cars handling during any form of accelerated manouver (lateral or otherwise), including the vertical domain caused by less than ideal road surface.
The range of adjustment you have is indeed quite wide and the effect very noticable. Try it !

Not wanting to state the obvious but the car "swims" on the air in your tires. The less pressure the more that car will "swim" in the lateral direction as the tire walls will offer less resistance to this movement (effectively the car moves laterally relative to the thread surface). Worse, this effect has a resonance and can contribute to the "ringing" that Gary is refering to by allowing a higher amplitude of the unwanted excursions. Higher tire pressure dampens this effect but you pay in lowered comfort. Nothing is free...

Rainier

chuckbdc

Re squish:
Assume that all of the cars tested had PASM, reasonably close temperatures, Gary, and his attention to the variables of particular interest. Accept that the tires in all of the cars he drove were not so far apart in pressures.

I believe that the effect of Sport PASM- lower center of gravity, stiffer springs and in particular stiffer roll bars- is to reduce the suspension rebound from transients that Gary described feeling in his car after driving PDCC. When those transients are due to lateral motions, the effect could be understood as a a reduction in time to CORRECT or, less squish. It must be that less squish that some testers, used to a given degree of squish, perceive as less "feel".

When transients are vertical, as in bump rebound, less squish = more harsh, the other road "feel" feature of your grandfathers 911. It seems reasonable that with dynamic roll bar stiffness, PDCC provides yet less squish and less harsh. Or better control and a change in signals to body and brain with appropriate physical and perceptual effects.

So, all the fruit are very tasty and ready to eat, and none are over ripe. Pick the one that feels good to a gentle squeeze.

Rainier_991

So, I could refactor:

Squish = SPASM(no PDCC) ~ PASM(PDCC)
Harsh = SPASM(no PDCC) > SPASM(PDCC) > PASM(no PDCC) > PASM(PDCC)

Thus follows:

Choice for less squish and least harsh = PASM(PDCC)
Choice for least squish less harsh = SPASM(PDCC)

But feel=harsh (can't deny there is a relation)

Thus:

Feel = SPASM(no PDCC) > PASM(no PDCC) > SPASM(PDCC) > PASM(PDCC)

Rainier
(OK, I'll stop...)

chuckbdc

[QUOTE=Rainier_991;10162604]......

But feel=harsh (can't deny there is a relation)
QUOTE]

Suddern vertical motion is the primary source of harsh-feel. Control over vertical motion at a given speed allows it to be tuned. The tradeoffs are satisfying the suspensions and the drivers, whose bump stops may vary.

So your next set of equations needs to work in the squish sensitivity, (which may or may not be actual squishiness (contemplating all the human variables)) of the wetware to hardware and software control. This may correspond to my theory of ripeness.

Rainier_991

[quote=chuckbdc;10162767]First or second theorem of ripeness ?
PASM does the job of vertical harshness control, PDCC decouples left/right by allowing use of more flexible sway bars and thus aids the PASM (in cases of uneven road surface). However what controls squishiness ? Is that not dynamic engine mounts, even the tires ? Have we considered the slightly more favourable fore/aft mass distribution of the 4 wheel drive - would that not counteract the rear pendlum and thus reduce squishiness or Gary's noted "ringing" ?
PDCC's ultimate reason for being in the fruit basket is avoidance of roll - but that is not material for typical Carrera road driving - so it's primary purpose for most of us is its secondary effect - that of aiding the PASM to even greater performance (or softness - a more favourable variation of squishy).

Right. I need a banana (soft, not squishy). My Porsche dealer is going to have to adjust their vocabulary next time I'm in line to order a Porsche...

Rainier

chuckbdc

[quote=Rainier_991;10162835]If I understood Gary, the main squish feel derives from the recovery from roll in cornering (eg the CORRECT). If so it would be the springs and rollbars that are the key variables. That fits with early reports by journalists Chris Harris and others, including a couple who point out that lowered, stiffer aftermarket tuner cars felt "more traditional." It also fit my personal (self defined authoritative expert) determination that I liked Sport PASM better than just PASM.

But a clarification for your modeling: there is car ripeness (based on suspension options), and driver ripeness (based on aging options).

hlee1169

Gary, great post, thanks for taking the time to write it up.

My own experience in tracking both a 991 S cab with PDCC and a 997.1 GT3RS is that the 991 has a bigger dynamic range, in audio speak. It flows superbly on street with bad pavement, yet feels stable on track. 991 gives me confidence to push harder on track. GT3 is more raw (as in feeling more noise and vibration), may have higher limit on track, but it does not give me the confidence to push it further. In fact, I've already spun out twice at Laguna Seca in the GT3, after driving the 991 for 6 track days at the same track without incident.

Best time in 991 S cab: 1:49
Best time in GT3RS: 1:51

I am pretty certain that I can improve my skills further, but 991 w/PDCC is just so stable in corners, and this leads to bigger confidence to explore the limits, where in the GT3 I have to trust the car will stay planted and the rear will not swing around.

Really looking forward to the 991 GT3 to see how it will do.