I bought a 48' trailer once that had 3 golf balls in each tire. I suppose they were there to balance them. I only found out about them as I replaced tires on it. It was funny, they were worn absolutely slick when they came out.

'65 C-10, 65 L-60, 65 C-80, 72 C-60 & and a bunch of old Chevy cars.
Never time to do it right, always time to do it over.