21 inch on the older cayennes will only slightly stick out. the extenders for the older cayenne are not as smooth as the newer ones. My dealer advised me te go just for the 21 rims without the extenders...

 

Any pics of 21" wheels without extenders? Sorry for digging up old post.

 

without the rim extensions and 21 inch wheels.

 

It looks great. Any problem with excess debris kicking up? I think the arch extensions look tacked on- which is what they are, but you know what I mean..

 

The arch extensions look indeed tacked on, and are on the older Cayennes not in the smooth surface available but only as a rough surface. The extra spray is indeed somewhat more but not that worrysome. You'll have more dirt on the rear of your Cayenne than on the sideskirts, if you know what I mean.

The 21 inch wheels do not flare outside the arches. It still looks good. No tire sticking out of the arches... Have no problems with the sport setting and the lowest setting of my air suspention. no touching of wheel to arch what so ever.