C4S in the snow, how come the front wheels do not spin?

[kazino]

http://www.youtube.com/watch?v=K8M6oB8NWiI&fea...

I have read the articles on PH about the 4wd system in the 996, and it seemed that if the rear wheels spin at a different rate to the front then power would be transferred to the front wheels but that does not appear to be the case in this video?

[sneaky schnell]

kazino said:

http://www.youtube.com/watch?v=K8M6oB8NWiI&fea...

I have read the articles on PH about the 4wd system in the 996, and it seemed that if the rear wheels spin at a different rate to the front then power would be transferred to the front wheels but that does not appear to be the case in this video?

I have to assume he wasn't worried about hitting the kerb.
Exhaust sounds good though.

[Lawsy]

'Probably' because the maximum percent of power distributed on the front at any given time is 22%(i think??) Power is distributed from 5 to 22 percent on the front wheels and from 78 to 95 percent rear. So although the 4S is in fact 4 wheel drive, it is predominantly rear, thus the greatly rear wheelspin/slippage.

[Purple Tom]

I don't really know much about the Porsche '4WD' system - is drive to the front wheels apportioned via a viscous coupling or is it done electronically via some sort of electromagnetic clutch or similar (or even an electronic viscous coupling?)

If it's the latter then I imagine with the PSM switched off the car would become almost exclusively RWD, hence the large amount of rear wheel spinnage and no front wheel movement.

That video just goes to show how grippy winter tyres are though, I love them on my cars

EDIT - to satisfy my curiosity (as its unlikely I'll ever actually own a C4S or similar) I just did some reading. Looks like there's a centre diff driven by the gearbox which then transmits drive to the front and rear in a proportional way using electro-hydraulic clutches employing speed sensors on each of the wheels to determine which end needs the drive etc etc more witchcraft happens then the car moves. Mind you, that was referring to a 1989 Carrera 4 so it's almost 100% certain that that's not how it works anymore. To cut a long story short, now I don't know at all. Sorry!

Edited by Purple Tom on Saturday 14th January 11:50

[ZeroH]

The vc wont transfer drive until its fluid is hot enough which is most standing applications like getting yourself out of snow seems not to happen.

[Callughan]

Lawsy said:

'Probably' because the maximum percent of power distributed on the front at any given time is 22%(i think??) Power is distributed from 5 to 22 percent on the front wheels and from 78 to 95 percent rear. So although the 4S is in fact 4 wheel drive, it is predominantly rear, thus the greatly rear wheelspin/slippage.

On 996 40% can shift to front, on mine in the snow and rain the front would spin?

Karim best way to do is take your psm off, do a full bore launch when the roads are wet and you will immediately feel all the power shift to the front.

[Guyr]

Firstly you can only see one front wheel in the video, so it's entirely possible the other one is spinning, since the front diff is open ie not an LSD. The rears will spin both since I think it has an LSD as standard.

Worth noting that in really bad conditions the 964 C4 had the best (and unique) 4wd system, which had a manual diff-lock switch in the cabin, since the centre diff was mechanical (based on the 959) not viscous.

[MrCooke]

Guyr said:

Worth noting that in really bad conditions the 964 C4 had the best (and unique) 4wd system, which had a manual diff-lock switch in the cabin, since the centre diff was mechanical (based on the 959) not viscous.

A 964 C4 is the ultimate snow Porsche. Sideways everywhere but always with enough traction to keep you going forwards.

Get one and you will believe you are Juha Kankkunen.

[paulmon]

Another example of the 4WD not really being any use when you are stuck. The person in this video is someone who works for us and the reason he had parked on the grass was because the drive of the house was full of cars when he arrived. He got up the following morning after a monsoon and ...... well see for yourself.

http://www.youtube.com/watch?v=iV8pB6OQCTI

P

[Tino]

looks great without the front plate though!

[thegoose]

paulmon said:

Another example of the 4WD not really being any use when you are stuck. The person in this video is someone who works for us and the reason he had parked on the grass was because the drive of the house was full of cars when he arrived. He got up the following morning after a monsoon and ...... well see for yourself.

http://www.youtube.com/watch?v=iV8pB6OQCTI

P

Did he leave PSM on?

[TonyB66]

paulmon said:

Another example of the 4WD not really being any use when you are stuck. The person in this video is someone who works for us and the reason he had parked on the grass was because the drive of the house was full of cars when he arrived. He got up the following morning after a monsoon and ...... well see for yourself.

http://www.youtube.com/watch?v=iV8pB6OQCTI

P

Is that tyre smoke or the clutch burning?

[Helicopter123]

On a related note I've been told a 2 + winter tyres will get you further in the snow than a 4 with standard tyres.

Thoughts?

[gibbon]

Helicopter123 said:

On a related note I've been told a 2 + winter tyres will get you further in the snow than a 4 with standard tyres.

Thoughts?

Tyres are everything.

[Trev450]

Helicopter123 said:

On a related note I've been told a 2 + winter tyres will get you further in the snow than a 4 with standard tyres.

Thoughts?

Given the fact that I was able to get to places with my Cayman S with winters fitted last year where some 4x4's were struggling, I'd say yes.

[Magic919]

Helicopter123 said:

On a related note I've been told a 2 + winter tyres will get you further in the snow than a 4 with standard tyres.

Thoughts?

I'll let you know once we have some snow.

[melv]

MrCooke said:

Guyr said:

Worth noting that in really bad conditions the 964 C4 had the best (and unique) 4wd system, which had a manual diff-lock switch in the cabin, since the centre diff was mechanical (based on the 959) not viscous.

A 964 C4 is the ultimate snow Porsche. Sideways everywhere but always with enough traction to keep you going forwards.

Get one and you will believe you are Juha Kankkunen.

Yeh, but slowing down would NOT overcome the laws of physics!!!

[911tj]

theyre awesome in the snow.....

[OlberJ]

What looks like cold engined cars being bounced off the limiter

[MrCooke]

melv said:

Yeh, but slowing down would NOT overcome the laws of physics!!!

Which is why the lighter, skinnier tyres six-four is the one to have.