Snow tyres fitted to 996 4S

[gprosser]

295/35/18 Pirellis

 

[chriscoates81]

Is this to fit on 11" rims?

 

[MisterCorn]

This is the size I have for my winters, running on 11" rims.

MC

 

[Shurv]

I've got 10J with 265's for mine. Fronts same as std.

 

[ragpicker]

I used to have these on my 4S. They fit fine and are the only real size you can get for the 11j rears.

Only problem is that they set off the PSM light under hard acceleration, presumably because the front wheels are spinning faster than the rears.

Someone also mentioned that it may cause premature diff wear but this doesnt make sense as the viscous coupling only comes into play when the rear wheels are spinning faster than the fronts, not the other way around.

Also gives a slightly raised look to the rear of the car which I quite liked.

:thumb:

 

[MisterCorn]

Someone also mentioned that it may cause premature diff wear but this doesnt make sense as the viscous coupling only comes into play when the rear wheels are spinning faster than the fronts, not the other way around.

I don't think the viscous coupling knows which end is going faster, it sees a difference and reacts to that. Either way I don't see what it has to do with diff wear, unless someone is suggesting that due to the coupling transmitting more power all of the time to the front of the car the front diff has to do more work? I can see it might have an effect on the life of the VC though.


MC

 

[chriscoates81]

I thought 5% was the rolling radius tolerance. Not sure how 295/35 match tho.

 

[Red993C4]

Someone also mentioned that it may cause premature diff wear but this doesnt make sense as the viscous coupling only comes into play when the rear wheels are spinning faster than the fronts, not the other way around.

I don't think the viscous coupling knows which end is going faster, it sees a difference and reacts to that. Either way I don't see what it has to do with diff wear, unless someone is suggesting that due to the coupling transmitting more power all of the time to the front of the car the front diff has to do more work? I can see it might have an effect on the life of the VC though.

MC

The viscous coupling reacts to any differences in speed between the input and output shaft, regardless of which is running faster, by heating up the fluid and causing it to lock up the coupling.
Spending most of its time at high temps would surely cause the fluid to break down prematurely. I suspect that the detrimental effect of mismatched tyres on the life of hydraulically controlled mechanical 4WD centre couplings is even greater than on viscous couplings though.
The flashing ABS warning light isn't meant to warn of possible harm being done to the viscous coupling so much as draw attention to the fact that the ABS system is working outside the parameters it was tuned for, so that it is a separate issue, and potentially a more critical one.

 

[Red993C4]

I thought 5% was the rolling radius tolerance. Not sure how 295/35 match tho.

2% is the figure usually quoted, and is most certainly the figure I've heard in relation to the 996 turbo's 4WD system.

 

[gprosser]

They fit on the 11J rears, with matching fronts as follows:

295/35R18 99 V PIRELLI - W 240 SOTTOZERO S2 N-2 (TL)

235/40R18 91 V PIRELLI - W 240 SOTTOZERO S2 N-2 (TL)

Did a lot of research on this, and they are well within tolerances with the above setup.

Got all 4 for a very reasonable €1050 fitted. Took 2 trips home to get the summers back however. Must get a roof rack ;-)

 

[chriscoates81]

They fit on the 11J rears, with matching fronts as follows:

295/35R18 99 V PIRELLI - W 240 SOTTOZERO S2 N-2 (TL)

235/40R18 91 V PIRELLI - W 240 SOTTOZERO S2 N-2 (TL)

Did a lot of research on this, and they are well within tolerances with the above setup.

Got all 4 for a very reasonable €1050 fitted. Took 2 trips home to get the summers back however. Must get a roof rack ;-)

Or a trailer