Thanks RC.

The US Porsche website finally has a Cayenne Tequipment section and Porsche is showing the same part numbers that you have for Winter tires on those rims. The only difference is, they are showing Dunlop Winter Sport tires for those part numbers: Porsche web page. They are speed rated to 118 mph (T).

The current Christophorus has winter tire recommendations and show the Dunlop Grandtrek 235/60 for the 18" wheels on the Cayenne. This tire is rated to 130 mph (H). I have not found this tire available in the US. I haven't looked very hard either though. Winter tires are not a big concern of mine where I live. Ron though, I bet he's worried!