Pendulum dynamics and AWD
04-18-2012, 01:42 AM
#1
Race Director
Thread Starter
Pendulum dynamics and AWD
Just curious how people see the issue of pendulum dynamics as it relates to AWD which has been available in 911's for years. With altered weight distrubution, drive torque shifted on demand between front and rear (software controlled, in fact), and the front wheels often pulling the car through corners the effects of pendulum dynamics have been greatly mitigated, and drive characteristics and even steering feel have been altered. Yet no one is complaining that a C4/S is a sellout to modernity and the ruination of traditional 911 values (nor should they; the 4's are great cars). I suggest that a 2wd 991 might be closer in handling dynamics to a 2wd 997 than a 2wd 997 is to an AWD 997, but I'm willing to be convinced otherwise by a good counter-argument.
Thoughts?
Thoughts?
04-18-2012, 02:08 AM
#2
Nordschleife Master
Mike: 4WD 997s exhibit just about the same pendulum dynamics as a 2WD (maybe a smidgen less). They just have more traction. I agree that the architecture transitions the pendulum swing to a front grab as the front engages, but the pendulum is very much there. Pendulum does not have to do with traction, but with geometry and mass distribution. I have many miles on 2WD and 4WD, as my previous car was a C4.
The 991 changed that geometry significantly. The 991 still has a shade of pendulum, but at much higher limits, beyond recklessness. A 991 feels like a balanced car such as an M3 or E63. That is what a 4"WB increase and wider front track do. For the Nth time: the 991 is a fantastic performer, that is not in question, but drastically different from what a 911 used to be.
The 991 changed that geometry significantly. The 991 still has a shade of pendulum, but at much higher limits, beyond recklessness. A 991 feels like a balanced car such as an M3 or E63. That is what a 4"WB increase and wider front track do. For the Nth time: the 991 is a fantastic performer, that is not in question, but drastically different from what a 911 used to be.
04-18-2012, 02:19 AM
#3
Race Director
Thread Starter
Thanks Tony. I'd seen comments in the past from people who felt that the 4's changed the handling dynamics of 911's more significantly than you suggest; apparently they were over-stating the case.
04-18-2012, 02:39 AM
#4
Nordschleife Master
And further clarification: pendulum dynamics is the lateral swing of the rear under lateral acceleration. Under traction it is felt as a lateral butt kick. Only beyond traction leads to significant oversteer. A C4/C4S compensates the loss of rear traction with the intervention of corrective front traction. Sure, from a traction perspective, near the limit, a C2 and a C4 behave differently. But that kick/swing in the rear is always there both on a 997 C2 or a C4.
The fun of driving a 911 (up to the 997) for me is the feel of the pants of that magical back kick/swing (under traction), at 6/10-7/10 under perfectly safe conditions on the right road. I suspect many Porsche drivers, even on his forum, never experience that. Either they drive very slow or too fast (tail out) and miss the sweet spot as they tend to be binary drivers and lack smoothness.
I tried to find that swing magic on a 991 and it isn't there, just linear traction on rails - great clinical performance no doubt. Beyond 7/10 it just 4-wheel-slides like a 'balanced' car. But if I wanted that there are many choices, even from Porsche.
The fun of driving a 911 (up to the 997) for me is the feel of the pants of that magical back kick/swing (under traction), at 6/10-7/10 under perfectly safe conditions on the right road. I suspect many Porsche drivers, even on his forum, never experience that. Either they drive very slow or too fast (tail out) and miss the sweet spot as they tend to be binary drivers and lack smoothness.
I tried to find that swing magic on a 991 and it isn't there, just linear traction on rails - great clinical performance no doubt. Beyond 7/10 it just 4-wheel-slides like a 'balanced' car. But if I wanted that there are many choices, even from Porsche.
04-18-2012, 02:53 AM
#5
I don't know about all this hocus pocus but I just bought a 997 C4S and absolutely LOVE the thing. I don't even think about it being awd or not awd. It's just point and shoot. I mean isn't that what the C4 is all about? Keep in mind I've been driving an 87 930 for the past 10 years....which is more like...think before you shoot. I mean if you chaps want to pontificate about pendulum dynamics, the 930 is your girl. And but of course I kept her!
Last edited by svb; 04-24-2013 at 05:40 PM.
04-18-2012, 04:48 AM
#6
Rennlist Member
Mike, I am planning a roadtrip to CA this summer, if it all works out, you should try my car to see for yourself. Could be good to debate 991 in person, over beers maybe! 
04-18-2012, 09:51 AM
#7
Race Director
pendulum dynamics has been dialed out of the 911 for years.
You would have to do something EPICALLY stupid to get the rear of my 993TT to come around at anything but serious track speeds.
You would have to do something EPICALLY stupid to get the rear of my 993TT to come around at anything but serious track speeds.
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04-18-2012, 12:52 PM
#8
Race Director
Thread Starter
04-18-2012, 01:28 PM
#9
Nordschleife Master
A smooth driver enjoys the feeling of pendulum dynamics at perfectly sane speeds without losing traction on any 996/997. I do. See post #4 above.
04-18-2012, 02:35 PM
#10
04-18-2012, 02:59 PM
#11
And further clarification: pendulum dynamics is the lateral swing of the rear under lateral acceleration. Under traction it is felt as a lateral butt kick. Only beyond traction leads to significant oversteer. A C4/C4S compensates the loss of rear traction with the intervention of corrective front traction. Sure, from a traction perspective, near the limit, a C2 and a C4 behave differently. But that kick/swing in the rear is always there both on a 997 C2 or a C4.
The fun of driving a 911 (up to the 997) for me is the feel of the pants of that magical back kick/swing (under traction), at 6/10-7/10 under perfectly safe conditions on the right road. I suspect many Porsche drivers, even on his forum, never experience that. Either they drive very slow or too fast (tail out) and miss the sweet spot as they tend to be binary drivers and lack smoothness.
I tried to find that swing magic on a 991 and it isn't there, just linear traction on rails - great clinical performance no doubt. Beyond 7/10 it just 4-wheel-slides like a 'balanced' car. But if I wanted that there are many choices, even from Porsche.
The fun of driving a 911 (up to the 997) for me is the feel of the pants of that magical back kick/swing (under traction), at 6/10-7/10 under perfectly safe conditions on the right road. I suspect many Porsche drivers, even on his forum, never experience that. Either they drive very slow or too fast (tail out) and miss the sweet spot as they tend to be binary drivers and lack smoothness.
I tried to find that swing magic on a 991 and it isn't there, just linear traction on rails - great clinical performance no doubt. Beyond 7/10 it just 4-wheel-slides like a 'balanced' car. But if I wanted that there are many choices, even from Porsche.
04-18-2012, 03:33 PM
#12
Nordschleife Master
04-18-2012, 03:56 PM
#14
How does this pendulum dynamic differ from oversteer? Sometimes the rotation is intended and anticipated. Sometimes less so. The other day I picked my wife up at work for lunch. There was a lot of traffic. After a long wait for an opening to make my left turn I tooh advantage of a small break and accelerated aggressively into the turn. What I expected was a slight drift into the distant lane. However i didnt Notice the road was crowned and the car over rotated a few degrees as the off camber surface fell away. No big deal. Just a bit more spirited than I usually have with my wife in the car.
