Did I say four? I meant three.
I almost bought a solid 15 inch ball from Lawrence Christopher once - it weighs 400 pounds. If you recall, his workshop was on a hill overlooking the county road. He told me the last time he tried to move one it got out of control, rolled down the hill over 2 trees, across the road (no cars hit), and down the other side.
I looked at my Mustang, and decided against it.