hello mumbasic,
there are winter tyres for 20" cayenne rims.
We have them on my fathers cayenne. I drove in St. Moritz last year. No problem to drive on snow or ice, only the weight of the cayenne is the problem
. Breaking is a bit more difficult than with other cars on snow.
It is a continental 275/40 R 20 106V XL FR. You can drive 240 km/h with it (V - version).
Perhaps I can find a picture of it...