We discovered a curious pile of tiny metal balls in an abandoned truck parking lot, which was covered with fine gravel and rusted bolts. At first glance, they resembled miniature ball bearings, but they were far too perfectly round and smooth. Each sphere sparkled in the sun and appeared impervious to corrosion while being outside.
We tried to squash them but had little luck. I tried using a lighter to melt them, but it was worthless. The material was evidently quite tough. Their shape and uniform size made us wonder where they were from. I questioned a friend who has been in trucking for many years. He immediately identified the balls and explained: “These are balancing balls,” he explained. “They’re filled inside tires to balance the wheel while it’s rolling.”
Instead of placing weights on a balancing machine, drivers simply dump these balls into the tire. When the tire spins, the balls locate the proper position to balance the rotation. Cheaper and faster—especially for huge vehicles. Later, I conducted some study. It turns out that these balls are actually utilized in truck and off-road tires.
They’re made of hardened steel, which can tolerate high heat and pressure inside the tire without breaking or losing shape. They may have an anti-corrosion coating or be built of composite materials to save weight, but the most common material is steel, which is the strongest and most lasting. When the truck accelerates, these balancing balls distribute evenly inside the tire, automatically compensating for any imbalance—because a wheel might lose balance if the tread wears or the load varies. This way, the tire “adjusts” to various driving circumstances.