Vehicle tyre inspection

A tyre condition monitoring system comprising a sensing unit adapted for use with a tyre and placed a distance from a tread surface of the tyre to take a measurement of, or at least from which can be derived, depth of tread grooves(s) in the tread surface, the sensing unit being adapted for deployment by non-automated manual or mechanical placement at the distance from the tyre and to store and/or transmit measurement data from one or more of a set of tyres on a vehicle, wherein the sensing unit comprises a signal injector that emits signals to the tread surface and into the tread groove(s), a reflected signal receiver for receiving reflected signals resulting from the signals being reflected from the tread surface and the tread groove(s), and a light meter adapted to compensate for ambient light conditions at the tread surface, wherein the sensing unit is configured to measure the time-of-flight of the reflected signals, wherein the time-of-flight is used to take a measurement of or derive the depth of the tread groove(s) in the tread surface.