Method and system for wheel alignment of vehicles

A method for determining wheel alignment of a vehicle, which vehicle comprises a first wheel axle having an axle end with at least one wheel member at a respective longitudinal side of the vehicle, the method comprising the steps of:

• arranging, for each longitudinal side of the vehicle, a first and a second optical reference element, each having at least two measuring marks defining a horizontal reference line, at fixed positions at a measuring site and such that the reference lines are generally in parallel with each other, wherein the first and second optical reference elements are remote from the vehicle;
• positioning the vehicle at the measuring site, such that, for each longitudinal side of the vehicle, there is an unobstructed line-of-sight between the wheel members of the respective first and second optical reference elements,
• mounting an optical measuring instrument to a wheel member at each axel end of the first wheel axle, and
• mounting an optical measuring instrument to a wheel member at each axel end of a second wheel axle of the vehicle or to each end of a measuring rod mounted to the vehicle;
• determining a first relative position of each wheel member and each rod end to which an optical measuring instrument has been mounted, using the optical measuring instrument and the first and second reference elements arranged at each side of the vehicle;
• determining a first toe angle of the wheel member at each axle end of the first wheel axle using the optical measuring instrument and the first and second reference elements arranged at each side of the vehicle,
• determining a first geometrical centerline of the vehicle based on the first relative positions,
• rotating each wheel member approximately 180°,
• determining a second relative position of each wheel member and each rod end to which an optical measuring instrument has been mounted, using the optical measuring instrument and the first and second reference elements arranged at each side of the vehicle;
• determining a second toe angle of the wheel member at each axle end of the first wheel axle, using the optical measuring instrument and the first and second reference elements arranged at each side of the vehicle,
• determining a second geometrical centerline of the vehicle based on the second relative positions, and
• calculating an out of square of the first wheel axle based on the second geometrical centerline of the vehicle, the second toe angles, the difference between the first and second geometrical centerline and the differences between the respective first and second toe angles.