Did you keep the conti's on it?

I had this problem, this was my solution: I had changed the bolts to have the wheels fit and added universal bolts with nuts. When I changed my tires for the second time and added 305/30/22 to the rears, I had vibration. I went back to the tire shop and realized that the longer universal bolts were lose, so simple tightening of the bolts with a allen key resolved everything. This was my problem, so check it out and GL.

Post some pics of your ride.