J&J Demolition Derby, 5 p.m. Sept. 5, Fairgrounds Grandstand, Allentown Fair. It’s a Labor Day tradition at the Fair when the heavy-metal thunder of crashes and smashes rings out on the straightaway of the racetrack. As James Taylor sings in the song, “Steamroller,” that he wrote: “Well, I’m a demolition derby, yeah, A hefty hunk of steaming junk.” Drivers compete in qualifying heats until the last vehicle running qualifies for the feature to win the title, “The Beast of the East Champion.” Three fender-crunching heats, featuring full-size cars, 1980s or newer, and compact cars, return to the Fair. There’s a new exhibition of battery-operated riding toys and Power Wheels. The “Kids Power Wheels” exhibition allows children ages 4-10 to show off their driving skills on the historic racetrack where the likes of Mario Andretti, Johnny Parsons, Jim Hurtubise, Parnelli Jones, Tommy Hinnershitz and Bill Schindler competed in sprint-car races, sending rooster-tails of dirt into the air as they slid around turn four.