My white German Shepherd will chase an RC car until he can barely walk. If he was an older dog, I would be worried about a heart attack. Stop the truck and he will be right there barking at it, wanting the chase to be back on. He tried to bite it once and I told him no, since then, the chase has been on. He is about three years old, stands about 6'00 tall on his back legs and weighs 115 pounds. He is a beautiful boy and very long and fast. He looks more like a Great Dane in build, but definitely has those Shepherd ears and head. I have watched him chase a deer for over a mile, I have photos of him checking out a fawn. He is a gentle giant, but he sure likes the pursuit.
BB