tbarcelo

See my post #42. I suspect that PSM intrusion will significantly reduce as you put some wear on those rear tires.

Guybrush Wilkinson

Yes Dave, never seen winter this one.

However, trying the car on snow with studded tires would be very interesting. My previous car (Carrera 2 on the avatar) had manual gear box with no PSM was tricky to handle. I bet turbo AWD and PSM would make it a lot better winter car.

Anyhow, this baby of mine will flower the carage during winter.

DaveK

We've had snow in the UK the last few years - far more than we're used to, although negligible compared to what you guys get. I've driven my turbo both times and it's been fine - biggest problem actually is the height - because the tyre tracks in the snow leave a nice high ridge in the middle, the turbo acts a bit like a snow plough.....

Twinturbofan

You can count me in as one more tt driver with the same problem. I have a 2003 tip with 19" rims. 235 35 19 front 315 25 19 rear. Never had a problem until I replaced just the rear tires. Out on a spirited drive into a downhill left hander my right front brake went off hard enough to invoke ABS stutter, released, and then applied itself again. Scared the you know what out of me. I got a read out after of "implausable wheel speeds". Since then it has happened numerous times including once when simply coasting around a freeway offramp at very moderate speed. I now have to drive the car with PSM turned off. I do not think I will ever be able to mentally trust it when driving hard. Unless it has happened to you while really pushing the car, you can not imagine how disconcerting it is.

SSST

The differential in tire diameters for that combination are just barely in spec for a 996 TT. My guess is the new rears paired with worn fronts caused the accpetable differential to be exceeded and your PSM is reading it wrong in a cornering situation and activating too early.

I was looking at 19's and decided to stay with 18's because I couldn't get the tire diameters close enough with N rated tires to feel comfortable that I wouldn't have problems.

Just my .02 from the research I did.

TheKane

So I am blown away. I own three Porsches, and this makes me want to burn all of them to the ground. The PSM can't f*cking figure out that all 4 wheels are 19s, and that all 4 have new rubber? Why would any reading result in a slamming on of the front brakes, making the front dive and the nose of the car lurch toward the outside of the corner. How is this an acceptable failure state? I just spent a nice chunk of money replacing my left sensor. Porsche can lick my ***** for making such a crappy system. Now I have to drive with the PSM off? I don't mind in the dry because I do it anyway, but in the snow? Bull****. Shame on Porsche for having sh*t components.

"02996ttx50

i used to get abs/psm's when i ran 19's but only when rears were new, relative to old fronts etc. it seems to take a min for the ecu to figure it out.. but eventually does? sounds like your issue is more daunting..

TheKane

Same issue as the original poster. If every single one of my past vehicles, none of which were as premium as the 996TT (Subaru, AMC Jeep CJ7, Chevy Tahoe, etc.) can figure out aftermarket rims and new rubber, I expect Porsche to figure it out. I can't believe this issue has no fix.

"02996ttx50

another way to look at it might be that you are temporarily the proprietary custodian of a car with onboard diagnostics so precise, they can tell you when you have merely changed a tire(s)? or not

all kidding aside.. the cacophony of lights on the dash of this car can bring me x'mas joy, pretty much year round. i call it the joy of ownership.

dustinr

[QUOTE=TheKane;10327072]So I am blown away. I own three Porsches, and this makes me want to burn all of them to the ground. The PSM can't f*cking figure out that all 4 wheels are 19s, and that all 4 have new rubber? Why would any reading result in a slamming on of the front brakes, making the front dive and the nose of the car lurch toward the outside of the corner. How is this an acceptable failure state? I just spent a nice chunk of money replacing my left sensor. Porsche can lick my ***** for making such a crappy system. Now I have to drive with the PSM off? I don't mind in the dry because I do it anyway, but in the snow? Bull****. Shame on Porsche for having sh*t

Think the 996's are bad you should read about the AWD systems in the 964 cars, extremely complicated and extremely picky to tire size (has more in common with the Audi Quattro system than the cars since).

Simple put, the 996 Turbo was not designed around 19" wheels. I spoke with length to a Porsche engineer about it and he told me the lengths they had to go thru to get the 997's to work right with 19's. So now, all of the cars since the 997 can run 18" or 19" and I can't remember if they can run 20's or not, whichever model had the 20" option can run 20's too, 997.2? I know the 991 can. But largerr wheel size doesn't have anything to do with better handling, its simply for looks. The Porsche engineer told me they run as small a wheel as they can fit around the brakes, depending on the track, on their racing cars.

But no, the system in the 996TT isn't smart enough to adapt its parameters around whatever wheel and tire combo you fit. You said you cant believe the "failure state" is that unacceptible, but you are using a non approved combination of wheels and tires, and so you shouldn't be too suprised.

I think I was the original poster of this problem, years ago. It didn't make me long to learn to drive with PSM off while I had the 19"s and in fact I got used to driving with it off and after I switched back to 18"s I continued to drive with it off as the car was a lot more predictable at the edge without any interference.

Now as far as running PSM in the snow... It wasn't designed for that either. When driving in snow you are supposed to shut it off. I live in the Tahoe area so I had ample opportunity to drive the Turbo in snow and it actually does better with PSM off, especially from a stop. Once going you can switch it back on, but I found it to almost cause sliding because it was constantly apply a brake somewhere.

one of the quircks of the 996TT.

Edward 96 Viper GTS

these psm problems are occurring with the 2006 ish cayennes. very strange, no codes. dealer has no cure. problem still there after installing brand new michelin N spec tires.
very annoying.
to the dealers credit, they replaced the wheel sensors and control module. no luck.
i think its a programming issue with the psm and i think porsche is fully aware of the issue.

Th Dude

"Coasting" into corners will make the PSM kick on...in my experience. Adjusting the speed in the straight and smoothly applying the throttle the moment you enter the curve has eliminated the PSM from kicking on...for me. Yes, I had to learn how to drive this Porsche. My 928's were practically idiot proof.
YMMV
Abiding,
D

"02996ttx50

hello.

TheKane

Many good comments that I agree with. Some, I don't.

- In a $180K car, I expect the system to be able to handle a slightly larger diameter wheel/tire combo.
- Coasting or trail braking into a left-hander will set off the PSM/ABS.
- By failure state, I mean in the sense that if the system thinks you're sliding off the road, and it freaks out, it SHOULD NOT SLAM ON THE FRONT BRAKES, making the front of the car dive violently, pushing/sliding the front of the car to the outside of the corner. The fail state should be to NOT kick in the PSM, just the ABS, or some variant that is the opposite of what has been programmed.
- I am not thankful that it's not as bad as the 964. The 964 was made from 1989-1994, if I remember correctly. The system SHOULD be better for the newer model that was significantly more expensive with newer tech.
- Wider tires and tires with shorter sidewalls also handle better in the twisties, especially with the additional hp and torque.
- I turn off the PSM in the dry, but sometimes I forget, and it is quite startling when the issue happens. It's also hard to hit the PSM button while in a turn on a curvy road, while the car is lurching around due to the PSM/ABS turning on violently.
- This is my Tahoe car, so like you I use it in the snow quite a bit, and like you, I do turn off the PSM as the car works in the snow better without it, unless it's a very steep driveway covered in snow.