In the scene where Doc and Marty are hovering over Biff in 1955, Marty says "Lets land on him, we'll cripple his car"; right after that Marty is hanging on the side of the DeLorean than moves to Biffs car. Doc is still hovering; but when he hovers away off the the side you see the wheels folded up as if he is hovering, but under the wheel to your left you can see the actual wheel that is driving on the road.