When a pair of cars start to stage, I pick the one I feel will be the one most likely to pull the wheels and keep my camera pointed at it. As soon as I finished shooting the burst with the car doing the wheelie in the background, I turned to the people behind me and said "I guess I focused on the wrong car...". But I really like the way that one came out and the car in the background adds to the mayhem of the moment.
I personally like the Ranchero better so I have no qualms about the focus being on it instead of the wheelie car. Besides, and maybe not your intention, but imo, something that's showing action and has some blur to it is just fine so the pic looks good to this guy.