996 C4 wayward handling on slushy roads, anybody else exprience this?

I'm DD'ing a 2001 996 C4 Cabriolet, currently fitted with snow tires (Bridgestone Blizzaks that have about 4k miles on them, if that). Handling on dry roads is good (as expected) and on snow is OK, especially once I read on here about turning PSM off when driving on snow. Yes, it occasionally gets frisky and a bit sideways, but nothing I can't handle. However driving on slush seems to be almost impossible - it's like piloting a drunk elephant on rollerskates. The car is all over the place, it's threatening to spin at the slightest provocation at very low speeds (I usually have to pull over to let everybody else pass because I end up going 10mph slower than the normal flow of traffic) and even when going in a straight line, the rear of the car is gently swaying from side to side. Basically, it feels like it has zero rear end grip and not much more in the front, but only when driving on slush, not on snow. And no, I'm not driving on bald tyres, even if it feels like I do . Anybody else experience this? Any suggestions what can be done to improve this? So far I'm planning to have my local Porsche specialist check over the suspension and make sure the alignment is correct, but other than that I'm fresh out of ideas. And it's not like I have no experience driving in snow, it's not even my first winter with the 996 but after today's experience of nearly leaving the road *** backwards into oncoming traffic, I have a certain sense of urgency in addressing these issues or parking it for winter.

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You are going to get all kinds of advice to your questioning on how to stay on the road. Mine is "STAY OFF the roads when the condition cause you to loose traction. I was driving my C2 cab on newly falling ball type snow which barely covered the road surface. Granted I did not have snow tires and was caught out in an unexpected snow fall. I ever so gently lost the car on a slight right hand on ramp and slid into a guard rail. I am an experienced advanced Ex Cop driver but the car did not respond under these conditions and slid into the guard rail. The back end of the car on the way home after the bump was slipping and sliding as yours was and I decided never ever would I take the car out again in snowy conditions. I value my car much more than to risk it ever happening again. The power under the rear wheels would put these cars into a spin at the drop of a hat. In my experience they are only good under perfectly dry conditions. End of story. Now the idiots will come in and post to the contrary. Thanks for your honest posting..

My 996 C4S was my daily driver in all conditions. I also ran dedicated winter wheels and tires. I never experienced anything like you have described. Something sounds wrong... Maybe the alignment will help.

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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.

How's the tire pressure? are they unidirectional tires perhaps mounted in the wrong direction?

We're talking about a sports car with wide tires that has most of the power and weight in the rear driving on slush which IMO would be more slippery than snow... If PSM is trying to prevent the ends of the car from swapping then I'd leave it on. Even if I was to have fun with the car, it's not really all that much fun dragging it out of the ditch or finding the curb.

I leave PSM active in winter conditions. I did it with my 996 and I do with my 996. The only time that I deactivated PSM in winter conditions was when I needed all four wheels pulling. An example of this would be driving up a steep driveway in slippery conditions.

+1 Sounds like over inflated tires.....

Winter tires are designed to hold snow in their treads because snow-to-snow adhesion is better than rubber-to-snow. Slush is a different animal and your tires may not be well suited to this condition. If the sipes are too tight then the tires will clog up with slush and not clear. Tighter sipe design will hold snow well but will just float on slush. Most tires will have a rating for conditions like snow, slush, ice and rain. Your's probably score low in slush but great for other conditions. Added to this, Porsche tires are really wide relative to vehicle weight so the contract patch pressures are quite low. All in all results in a feeling not unlike hydroplaning and certainly won't inspire confidence. Maybe avoid driving your car in those transitional, slushy conditions and save it for days where it's colder or just wet and rainy.

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.

PSM is better at driving than anyone you know or will ever meet.

Disclaimer: I've never driven a C4, snow or otherwise. Here's my advice: https://www.enterprise.com/en/car-rental.html

@docmirror, not a bad idea, but try getting a rental car that has snow tires on it. Even here in skiing central that's a problem.

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 *

http://reno.craigslist.org/cto/5380795425.html

May need to re-calibrate PSM, if aliment was done.

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To be fair yours does have half of it's system removed so it's not really a C4 anymore 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?

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Thought you converted your C4 to a C2 no?

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.

^ it's a computer with sensors at each wheel and brain.... Turn PSM on you are overthinking it.

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.

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.

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.

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I notice it far more in my 958 than the 996, but that may be because I try to drive it like a 911 Nothing like turning it off and making the backend of a 5500# SUV drift though. That was a puckering experience!

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.

Congrats and enjoy

Excellent. Thanks for update.

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Yes, let PSM do it's thing, that's what you paid for...

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Leave PSM on! Now drive carefully, cautiously enough, that PSM never activates.

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Yes, ABS should be (re-)designed such that it doesn't activate unless VSC , Vehicle Stability Control, indicates that the car is not following the desired directional line.

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The front wheel aspect is passively controlled. Most drive, 80-90%, is to the rear wheels unless the F/R tire rotation rate is highly disparate, in which case traction control will intervene, braking the rear drive wheel(s) long before the front drive VC stiffens up.

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"far less twitchy.." Maybe because you have adapted to driving it more conservatively?

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Factory spec calls for toe out (positive toe) at the rear. Under way the driven wheels move forward a bit and better align with the direction of travel. With toe in the rear tires will wear very quickly. I've gone through a set in 8K miles.