An apparatus measures the tread of a tire on a vehicle, in which a laser line generator (34) generates an elongate pattern of light. Mirrors (36) are arranged to reflect light from the laser line generator (34) onto the rolling surface of the tire. Mirrors (36, 38, 42) are arranged to reflect light from different regions of the rolling surface of the tire towards a camera (32). The camera images the regions of the rolling surface of the tire. The apparatus may be hand-held or arranged such that a tire to be aged is driven onto or over it.