Tread for a Tire

A tread () for a tire () which has a tread surface intended to contact a road surface during running. The tread () has at least one cavity opening onto the tread surface when new, called external cavity (), which has length L, width W and central plane P. The external cavity () has bottom () and at least two opposite lateral walls () extending from bottom () and a mechanism () for ejecting stones during running, which has two protuberances () from bottom () of external cavity, which are disposed at least partially opposite one another at a distance d. Each protuberance () is inclined respectively from a lateral wall () of the external cavity () towards the central plane P. The distance d between the two protuberances () is less than or equal to 10% of width W of external cavity ().