A track system (40, 40', 40r, 40r') for use with a vehicle having a chassis, the track system comprising: an attachment assembly connectable to the chassis of the vehicle; a frame assembly disposed laterally outwardly from the attachment assembly and connected to the attachment assembly, the frame assembly including at least one wheel-bearing frame member (230 l, 230 t); a leading idler wheel assembly (400 l) at least indirectly connected to the at least one wheel-bearing frame member; a trailing idler wheel assembly (400 t) at least indirectly connected to the at least one wheel-bearing frame member; at least one support wheel assembly (410 a, 410 b, 410 c) at least indirectly connected to the at least one wheel-bearing frame member and disposed between the leading idler wheel assembly and the trailing idler wheel assembly; an endless track extending around the leading idler wheel assembly, the trailing idler wheel assembly, and the at least one support wheel assembly; at least one monitoring sensor connected to the endless track; and a track system controller communicating with the at least one monitoring sensor, characterized in that the at least one monitoring sensor includes: - a flexible foil connected to an inner surface of the endless track, and - an array of sensing devices (1122, 1152), wherein the at least one monitoring sensor is configured to: - determine, at least indirectly, at least one of a state of the track system and a ground surface condition, and to - generate at least one signal indicative of the at least one of the state of the track system and the ground surface condition, the track system controller communicating with the at least one monitoring sensor for receiving the at least one signal indicative of the at least one of the state of the track system and the ground surface condition. an attachment assembly connectable to the chassis of the vehicle; a frame assembly disposed laterally outwardly from the attachment assembly and connected to the attachment assembly, the frame assembly including at least one wheel-bearing frame member (230 l, 230 t); a leading idler wheel assembly (400 l) at least indirectly connected to the at least one wheel-bearing frame member; a trailing idler wheel assembly (400 t) at least indirectly connected to the at least one wheel-bearing frame member; at least one support wheel assembly (410 a, 410 b, 410 c) at least indirectly connected to the at least one wheel-bearing frame member and disposed between the leading idler wheel assembly and the trailing idler wheel assembly; an endless track extending around the leading idler wheel assembly, the trailing idler wheel assembly, and the at least one support wheel assembly; at least one monitoring sensor connected to the endless track; and a track system controller communicating with the at least one monitoring sensor, characterized in that the at least one monitoring sensor includes: - a flexible foil connected to an inner surface of the endless track, and - an array of sensing devices (1122, 1152), - a flexible foil connected to an inner surface of the endless track, and - an array of sensing devices (1122, 1152), wherein the at least one monitoring sensor is configured to: - determine, at least indirectly, at least one of a state of the track system and a ground surface condition, and to - generate at least one signal indicative of the at least one of the state of the track system and the ground surface condition, - determine, at least indirectly, at least one of a state of the track system and a ground surface condition, and to - generate at least one signal indicative of the at least one of the state of the track system and the ground surface condition, the track system controller communicating with the at least one monitoring sensor for receiving the at least one signal indicative of the at least one of the state of the track system and the ground surface condition.