Ever heard of this?

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Found on Sheldon Brown:

Tire Savers

Some punctures are caused by glass slivers or thorns gradually working their way through the tire tread. What can happen is that a small sharp object may be picked up by the tire, then gradually work its way in over the course of several tire revolutions. The pointy thing is driven in like a nail into wood by repeated blows against the pavement. A formerly popular device called a "tire saver" or "flint snatcher" used a loosely spring piece of wire (generally made from a bicycle spoke) to constantly brush the tire tread in hope of dislodging glass slivers and the like before they could penetrate all the way to the inner tube.

These are of dubious value in practice, but may be of help in backward areas where throwaway beverage bottles are still legal, and glass slivers are a major problem.


Also found this pic on the net.