Frankie Muniz is back to business. The “Malcolm in the Middle” alum returned to Instagram with an unexpected video about tire safety Saturday — just one day after revealing he had hit “rock bottom” following a “nightmare” six weeks. In the clip, the 40-year-old actor demonstrated the “old penny test” by sticking a coin into the tread of a tire to determine whether it needs to be replaced. “The old penny test still works. Insert a penny into the tread with Lincoln’s head facing down,” he captioned the video. “If you can see the top of his head, your tread is at (or below) 2/32″ — that’s the legal minimum and a safety problem in rain.” The…
