996 C4 wayward handling on slushy roads, anybody else exprience this?
01-06-2016, 01:01 PM
#17
I hadn't really thought of that before. Since you can't really turn PSM completely off in a C4, what happens to PSM in the RWD conversions? Does it get flakier because it can't make the front wheels do anything or is it smart enough to figure it out? Without the front drive shaft does turning PSM off truly turn it off or is it still partially enabled?
01-06-2016, 01:09 PM
#19
Race Director
Yes, my C4 is currently a C2 - but I have not driven it in the slush since the conversion. Since the amount of power going to the front wheels is minimal unless the rear wheels are slipping, removing the FWD stuff doesn't have as much an impact as you think it would - but it sure does make the car more fun to drive.
Interestingly, PSM is far less twitchy without the front wheel drive components.
Interestingly, PSM is far less twitchy without the front wheel drive components.
01-06-2016, 01:19 PM
#20
Burning Brakes
Originally Posted by DTMiller
PSM is better at driving than anyone you know or will ever meet.
01-06-2016, 01:21 PM
#21
Maybe I should have ours dyno'd to see if the power is way down or something...
I have to actively try (or do something stupid) to get PSM to kick in. It's not like I baby it and don't toss it around either. PSM is, unobtrusive in our C4.
I have to actively try (or do something stupid) to get PSM to kick in. It's not like I baby it and don't toss it around either. PSM is, unobtrusive in our C4.
01-06-2016, 01:23 PM
#22
Race Director
My PSM has always been very twitchy - the combination of 19" wheels, rubber-band tires, and a very taut suspension result in more bounce than a stock 996 wheel experiences. PSM got less twitchy once I increased the ride height by about half an inch.
01-06-2016, 03:55 PM
#23
Rocky Mountain High
Rennlist Member
Rennlist Member
I found the PSM system in my 996 to be more invasive than my 997 or my Cayenne. The 997 lets the rear end come out and it gives you a chance to correct it before it intervenes. It allows for even more slip in sport mode.
01-06-2016, 04:09 PM
#24
Nothing like turning it off and making the backend of a 5500# SUV drift though. That was a puckering experience!
01-14-2016, 11:41 AM
#25
Track Day
Thread Starter
To partially conclude the saga - had the alignment checked and redone at the local Porsche specialist. They found that the driver's side rear wheel had slight toe out instead of the required toe-in. Re-setting the alignment to factory specs made the car noticably more stable even on dry roads, and the drive home last night in a snow storm (first snow since the work) showed that the worrying instability from the back end has gone, too.
01-15-2016, 05:35 PM
#28
Drifting
If you aren't trying to push limits, why would you turn PSM off? Especially in such conditions. It's there for a reason and it does it's job really well under normal driving. 
Even in adverse conditions (e.g. rain/snow/ice/etc...) the only time PSM has ever kicked in on me is when I get a little stupid for the conditions (almost always taking a corner faster than I should).
+1
Not to start another tire discussion, but even with summer tires in such conditions I've never had that kind of thing occur. About the closest I can relate is on badly plowed roads where tire ruts have formed and refrozen. It wants to (naturally) follow existing ruts and will get pissy if they aren't going the direction I want to go.
Even in adverse conditions (e.g. rain/snow/ice/etc...) the only time PSM has ever kicked in on me is when I get a little stupid for the conditions (almost always taking a corner faster than I should).
+1
Not to start another tire discussion, but even with summer tires in such conditions I've never had that kind of thing occur. About the closest I can relate is on badly plowed roads where tire ruts have formed and refrozen. It wants to (naturally) follow existing ruts and will get pissy if they aren't going the direction I want to go.
01-15-2016, 05:46 PM
#29
Drifting
Thanks everybody for their suggestions and comments.
I'll check the tire pressures again this morning, I'm pretty **** about correct tire pressures and I'm pretty sure they're not overinflated. But it's worth checking anyway, same time as I'll check that they're mounted correctly.
Someone on a more motorsports oriented forum I posted the same question on suggested that it sounded to him like the rear had some toe out. That's actually exactly what it feels like, based on my experience driving a car on the track that has a slight rear toe out.
Re PSM on vs off - leaving it on when driving on snow turns the car into an understeermonster in tight corners and I've had it briefly lock up one of the front wheels more than once when they should actually be helping with traction. On slush, it usually doesn't kick in until it's too late anyway. Dennis C pretty much put it the way I experience it at well, turning PSM off seems to help getting the AWD working better when needed, at least right now.
@HurdiGurdiMan, if I can't find/have my shop find a mechanical or setup reason for my driving experience, I will park it for the winter - I'll have to buy an SUV or something like a Subaru to get me to work, but I really don't fancy driving off a 100' cliff...
Unfortunately if I have to park it for the winter, it'll be so I can sell it in spring - I have too many, err, enough cars as is and if I can't make the 996 work as a year-round car to the extent I have to buy another one, it will have to go.
I'll check the tire pressures again this morning, I'm pretty **** about correct tire pressures and I'm pretty sure they're not overinflated. But it's worth checking anyway, same time as I'll check that they're mounted correctly.
Someone on a more motorsports oriented forum I posted the same question on suggested that it sounded to him like the rear had some toe out. That's actually exactly what it feels like, based on my experience driving a car on the track that has a slight rear toe out.
Re PSM on vs off - leaving it on when driving on snow turns the car into an understeermonster in tight corners and I've had it briefly lock up one of the front wheels more than once when they should actually be helping with traction. On slush, it usually doesn't kick in until it's too late anyway. Dennis C pretty much put it the way I experience it at well, turning PSM off seems to help getting the AWD working better when needed, at least right now.
@HurdiGurdiMan, if I can't find/have my shop find a mechanical or setup reason for my driving experience, I will park it for the winter - I'll have to buy an SUV or something like a Subaru to get me to work, but I really don't fancy driving off a 100' cliff...
Unfortunately if I have to park it for the winter, it'll be so I can sell it in spring - I have too many, err, enough cars as is and if I can't make the 996 work as a year-round car to the extent I have to buy another one, it will have to go.
01-15-2016, 05:51 PM
#30
Drifting
My C4 does not handle well in the rain, and it handles even worse in slush. Much like my Corvette, the C4 likes to 4-wheel hydroplane in any heavy rain or slush.
I'm also in the "PSM sucks when traction is an issue" camp - diving into ABS when it's slick is a recipe for rear-ending someone.
Following is a transcript of hitting the brakes hard enough in slush to activate ABS:
*thud* (foot hits the brake)
*chugga chugga chugga* (ABS pumping)
"Shii
IIii
iiiii
IIiii
T!
*bang*
*tinkle tinkle*
I'm also in the "PSM sucks when traction is an issue" camp - diving into ABS when it's slick is a recipe for rear-ending someone.
Following is a transcript of hitting the brakes hard enough in slush to activate ABS:
*thud* (foot hits the brake)
*chugga chugga chugga* (ABS pumping)
"Shii
IIii
iiiii
IIiii
T!
*bang*
*tinkle tinkle*