The invention relates to a wheel guide rail (9; 10; 13; 14) for a car wash system for laterally delimiting a travel range (4) of a vehicle to be treated in the car wash system and a car wash system comprising treatment devices (1, 1′, 3, 3′) that can travel along a direction of travel (F) for a vehicle to be treated, a pair of wheel guide rails (10, 10′) disposed at the wash system floor (B) between the treatment devices (1, 1′, 3, 3′) and running in the direction of travel (F) and at a distance from one another perpendicular to the direction of travel (F), said guide rails delimiting a lateral travel range (4) for the vehicle. The object of facilitating a safe and damage-free treatment and cleaning of vehicles is met by the invention by a wheel guide rail, wherein at least one distance sensor (9f; 11; 13f; 14f) is provided in the guide rail (9; 10; 13; 14) for measuring the distance from the guide rail (9; 10; 13; 14) to an outside of the wheel and/or side of the vehicle, a car wash system comprising such wheel guide rails and a method for centrally positioning a vehicle within a vehicle range (4) of a car wash system.