14 September 2018

Wheel alignment explained | Factors | Steering geometry | Linkage

What is wheel alignment?

Wheel alignment is the positioning of the steered wheels to achieve the directional stability during straight-ahead position, perfect rolling condition on steering and recovery after completing the turn. 

Factors of wheel alignment : 

Toe in Toe out

Wheel alignment is used in connection with the stability and control of the vehicle while in the situation of motion. It means that while moving straight ahead the wheels should be parallel. In the event when they are pointing inward, they are said to toe in whereas if they are pointing outward they are said to toe out. Both these situations are undesirable because in either case while rolling forward, each wheel will be simultaneously slipping laterally due to which a continuous cross-tread scrubbing would take place. 

For good handling, steering, and vehicle stability, it is also necessary that 
  • There should no be any setback, which is said to be the distance between the placing of the front tyres. In other word set back is a condition in which one wheel on an axle is in front of or behind the other wheel in relation to the chassis frame. When a set back of less than 6 mm is considered normal tolerance by some manufacturers. 
  • The thrust angle should be zero. Thrust angle is the angle made by the thrust line with the longitudinal centre line of the vehicle. If the thrust angle is not zero, the vehicle will dog track the steering wheel will not be centred. When the thrust angle is zero, rear wheels follow the front wheels properly. Obviously, for this condition, all the four wheels should be parallel to the frame. This is called tracking. 
Set backThrust angle

For effective steering under all conditions and at all loads, it is very important to consider and understand the factors which influence the stability and control of the vehicle. The factors are following below : 
  • Factors pertaining to wheels 
  • Steering geometry
  • Steering linkage
  • Suspension system 
Factors pertaining to wheels : 
  • Balance of wheels 
  • Inflation of tyres 
  • Brake adjustment 
Steering geometry : 
  • Camber 
  • Caster 
  • Toe-in 
  • Toe-out
Steering linkage :
  • Kingpin inclination ( Steering axis inclination )
  • Combined angle and scrub radius 
  • Over-steer 
  • Under-steer