I have the same vibration on my '03 Cayenne S with the 20" sport design wheels running Michelins. Had it since the car was new. I guess I'd better have the dealer check the alignment settings and re-balance the wheels and tires. It's really putting me off the Cayenne.

 

Rockit, the problem that you mentioned in the post is a notorious problem with Kumho tires (even though you don't have Kumho's), but Kumho reps. have acknowledge that. The nylon that surrounds the steel belt inside the tire cools down and becomes out of round, i.e. flat spots, but because of nylon being flexible when it is heated up again by driving, the tires once again become round. This problem is even worse in the months we are in now because of the Summer heat, and cold concrete at night.

 

Well it appears that Porsche is somewhat aware of the vibration in the steering wheel issue. Since it is intermitent and varies based on road surface, they indicated that the culprit is most likey the servotronic steering control component. Porsche does not feel a recall is warranted at this time. The truck is in the shop and they will try to tweak the balancing and alignment to see if they can minimize the problem...I will post my impressions and the result of the dealer diagnosis when I get the car back

 

Well after adding new rubber and alignment, still had vibration. Apparently the servotronic steering mechanism is very sensitive to road forces. They decided to re-check the balance of the wheels they put on two weeks prior and they were off by 10 grams or so on each wheel. Supposedly they were in balance the first time. Well after the final balance, the car is vibration free!!! I guess that hunter road force balance machine is tricky to get right, especially with bigger tires/wheels