Truck Tire Centers, in our story on BFI (“Fleet View,” pages 8-13 of this issue), mentioned a phenomenon known as “brittle” or “burnt” beads.
Overheated brakes can generate excessive heat, which is conducted through the brake drums to the wheels and from the wheels to the beads.
Enough heat, and beads can “cook” until they’re rock-hard, brittle and “crystallized.” In this state, they can no longer provide a good seal against the wheel flange, and the next tire tool that touches them can break them like glass.
What causes the brake overheating? Besides a malfunction, like a dragging shoe, this can also be the result of frequent stops and insufficient drum ventilation – a vocational hazard that sometimes afflicts buses and garbage trucks.
Although any tire can suffer this kind of damage, it’s often seen on the inner tire of a dual assembly, but not the outer one, probably because the inner tire is closer to the heat source, the brake drum. Unfortunately, the condition cannot be repaired, and the tire must be scrapped.