I had the same thing happen on a ride coming back to Detroit from Ann Arbor, but in my case the car wheel made contact with the top of my front tire. I had just crossed a major road and had stopped to check the road name and my directions. A few seconds after I started riding again something flashed in front of my face and the bike was torn sideways. Fortunately I was only going a few mph and I stayed upright. Glanced to my left and saw the car wheel hit the curb and bounce way up in the air before disappearing across a vacant lot and into a gully. Looked over my right shoulder and there was a car in the median with a missing rear wheel. Traffic on that road was going about 50 mph so that's probably the speed of the car wheel.
The car tire must have just barely nicked the top of my front tire since the wheel was only slightly out of true and I was able to continue my ride. The driver was still walking across the vacant lot to retrieve his wheel/tire when I left.