Disclosed is a wheel probe for use on a pipe inspection vehicle. The wheel probe comprises a annular perspex outer rim with a polyurethane tire mounted on a hub assembly which, with the hub, defines a fluid-tight chamber containing an acoustic coupling fluid. A number of ultrasonic transducers are located inside the chamber and are positioned close to the inside circumferential surface of the rim. The hub assembly is carried by a spring loaded carriage which is secured through which ultrasound will pass.The wheel probe includes a guide wheel on each side. The guide wheels are carried by the carriage but are moveable bodily relative to the center of the hub assembly, and when deflected, they operate on the assembly to move the wheel probe to ensure that the outer rim of the wheel is correctly aligned relative to the pipe.The wheel probe has a number of shields spaced around its periphery. The gaps between the shields define operating "windows" through which the rim of the wheel probe projects to contact the pipe. The shields are located close to the bore of the pipe so that if the probe encounters an obstruction the shield snags on the obstruction, is pulled between the rim and the pipe to lift the wheel over the obstruction, and turns on to the next operating "window."Cam followers are provided to hold the shields in position.