It can really be disconcerting when you pick out a car to focus in on, follow it thru turns 3 and 4, and then, right when you're ready to shoot, you see nothing but a front grill in the view finder! Definitely pays to stay alert.....
I know this driver quite well, after he got it stopped a few feet away, I wandered over and told him that my zoom is working quite well, thank you, he really didn't need to come in for a close up!