# Car wheel alignment

Parameters relative to wheel alignment:

• VEHICLE AXIS OF SYMMETRY is a line going through the centres of the front and rear axles.
• GEOMETRICAL DRIVE AXIS is a line which divides total rear wheel toe angle into two even angles and which the vehicle follows during straight ahead drive.
• CAMBER ANGLE is the angle between the wheel’s side-plane and the perpendicular. When viewed from the front or rear, the wheel leans outwards from the perpendicular, it is said to have positive camber (fig. 1). This measurement needs to be made with the front wheels set to the straight-ahead position.
• KING-PIN INCLINATION is the angle between the perpendicular and the projection of the king-pin axis onto a vertical surface perpendicular to the vehicle’s symmetry axis (when viewed from the front or rear) (fig. 3). The angle is positive when the upper part of the king-pin projection is inclined towards the vehicle’s symmetry axis.    • CASTER ANGLE is the angle between the vertical and the king-pin axis, when viewed from the side. The angle is positive when the upper part of the king-pin axis leans towards the back of the car (fig.4), and negative when leaning in the opposite direction.
• TOTAL TOE (FRONT OR REAR WHEELS) is the angle between the side planes of both wheels of the same axle, measured horizontally (fig. 5 & 7). This parameter may also be given a linear measure. Then, it is the difference between the distances separating the wheel rims of the same axle (front or rear), which is measured at the front and back of rim flanges horizontally. The total toe value is positive if the intersection of the side planes is in front of the tested wheels (towards the driving direction), and negative when the intersection occurs behind the axle.
• HALF TOE (FRONT OR REAR WHEELS) is an angle between the side plane of the wheel and the symmetry axis (fig. 6) when the wheels are set to straight-ahead drive. Individual front wheel toe should be calculated from “Toe partial” results read from the measuring units.
• TOE OUT ON TURNS is the toe difference angle between the in and the out wheels when turning the out wheel by 20° (fig. 10).    • LOCK ANGLES is the maximum possible inner and outer turn obtained with the right or left wheel (fig. 11 and 12). Measurement of this parameter is only possible with the use of electronic turn tables.
• THRUST ANGLE is the angle between the geometrical drive axis and the vehicle symmetry axis (fig.8). This angle is positive when the geometrical drive axis is leaning right from the vehicle symmetry axis.
• WHEELBASE DIFFERENCE is the angle between the front and rear axis (fig. 9).
• INCLUDED ANGLE is the sum of the front camber angle and the corresponding king-pin inclination angle.    