Wheel Alignment is the process carried out after balancing all four wheels and mounting them to the vehicle. When all four wheels are mounted to the vehicle, it must run on the road in a straight line with dynamic stability. For this, the vehicle manufacturer has specified certain angles at which each wheel has to be mounted onto the vehicle axles. These specified angles are called Wheel Alignment Specifications.
If the wheels are mounted conforming to these specifications, the vehicle will travel on the roads without any vibration and with less friction.
The following are the Wheel Alignment angles for Light Vehicles.
1. Camber
2. Toe and total toe
3. Kingpin angle
4. Caster
If the wheels are mounted conforming to these specifications, the vehicle will travel on the roads without any vibration and with less friction.
All the above four parameters are angles measured in degrees and minutes. Among these angles, the Camber and Toe are the angles pertaining to the wheel position and therefore called Wheel Angles. The Caster and Kingpin angles pertain to the angle of the Steering Axis, which is the axis located in front of the vehicle and acts as a fulcrum for the front wheels to turn during steering. These are called Steering
Axis Angles.
The above four angles are considered to be very important angles for Wheel Alignment. Apart from the above four angles, the following angles/parameters also pertain to Wheel Alignment geometry.
1. Included Angle
2. Toe out and Turns
3. Lock Angle
4. Ride Height
5. Track width and Wheelbase
Now let us understand all the above angles and parameters in detail.
Camber
When we view the front wheels of a vehicle standing in front of the vehicle, though the wheels seem to be standing perpendicular to the road, in reality they are not. They will be inclined to the true vertical position either towards the inside or towards the outside of the vehicle. This inclination is called Camber. As seen in Figures 1.1 and 1.2, the inclination towards the outside of the vehicle is called Positive Camber and the inclination towards inside the vehicle is called Negative Camber. For all vehicle models, the specification of the Camber is decided by the vehicle manufacturer based on the weight of the vehicle and the maximum number of persons proposed to be travelling. Therefore the Camber can be called a Load Bearing angle. If the Camber is not set as per the specification in a vehicle, it will lead to tapered tire wear either on the inner side or on the outer side of the wheels .
Fig 1.1 Negative Camber Angle
Fig 1.2 Positive Camber Angle
Toe and Total Toe
If a vehicle is viewed from its top, the left and right wheels of both the front and rear sides will be seen inclined either towards the inside of the vehicle or towards the outside of the vehicle. This inclination with respect to the Geometric Centerline (GCL) is called Toe angle. As shown in Figures 2.1 and 2.2, if the inclination is towards the inside, it is called Positive (+) Toe and if the inclination is towards the outside, it is called Negative (−) Toe. The Positive Toe is also called Toe-in. Similarly, the negative Toe is called Toe-out also in sign. This means if the left Toe is positive, the right Toe will also be positive and vice versa.
Total Toe
Total Toe is the sum of the Left Toe and the Right Toe
Total Toe = Left Toe + Right Toe
The vehicle manufacturer determines the Toe specification considering the tractional friction and the Dynamic Stability of the vehicle during its motion on the road. If the Toe is not as per specification in a vehicle, the tires will wear out rapidly. For this reason, the Toe is considered a very important and critical angle of Wheel Alignment.
If the Toe is not within limits, it will result in the following bad effects.
1.Abnormal tire wear.
2.Vehicle pulling to one side while driving.
3.At high speeds, if the brake is applied suddenly, the vehicle, instead of stopping in the same line of travel, will get dragged to one side and then stop. This may lead to accidents.
4.Steering Cross (crooked steering) after alignment.
5.Improper Toe leads to feathered wear at the edges of tires.
Reason: Excess Toe-in or less Toe-out
Reason: Less Toe-in or excess Toe-out
In a vehicle, if the Toe is not within specification, it leads to abnormal and severe tire wear. Therefore, extreme care must be taken to ensure that the Toe is set within the specification in a vehicle.
Fig 2.1 Toe In Angle
Fig 2.2 Toe Out Angle
Kingpin Angle
When the steering wheel of a vehicle is turned, the front wheels turn using an axis as a pivot. This pivotal axis is called Steering Axis. In practice, it is also called Kingpin. There is a Steering Axis on the left side and also on the right side fitted on the Front Axle. In each Steering Axis, there are two bush bearings, one at the bottom and the other on top of the axis. The wheels are mounted to these bushes, and hence these
bush bearings enable easy turning of the wheels while steering the wheels. When viewed from the front of the vehicle, both the left and right steering axis will be seen inclined towards the inside as shown in Figure 3.1 This inclination with respect to true vertical is called the Kingpin Angle. The Kingpin angle is always inclined towards the inside of the vehicle. Kingpin angle is also called Steering Axis angle. Kingpin angle is a load bearing angle. It guides the vehicle for smooth traction, particularly on curves. The Kingpin angle is a fixed angle and cannot be corrected during Wheel Alignment. But this angle is measured during Wheel Alignment. If the Kingpin angle is deviating from the specification, it can be corrected only in the workshop and not in the Wheel Alignment Center.
Fig 3.1 Kingpin Angle
Caster
Caster is the angle between the true vertical and the steering axis when viewed from the side of the vehicle. As shown in Figures 4.1 and 4.2, if the inclination is towards the back of the vehicle, it is called positive (+) Caster, and if the inclination is towards the front of the vehicle, it is called negative (−) Caster.
The Caster angle helps in guiding the vehicle to travel in the desired direction. This is a direction control angle. For example, let us take a bicycle on the road the extension of the pipe connecting the handlebar and the wheel center touches the ground, little ahead of the point at which the wheel is touching the ground. This aspect guides the direction of the wheel when the handlebar is turned or makes the bicycle travel in the direction which we desire. The same principle is applied for Caster angle in cars and other four wheelers.
Besides directional control, the Caster is also responsible for the steering wheel to come back to the straight position after turning the steering wheel in curves. Generally, the Caster will be a fixed angle in vehicles and cannot be changed. But in some vehicles, the Caster angle can also be changed. If the Caster is not proper in a vehicle, then hard steering will be felt. Caster will not change due to the normal wear and tear of the vehicle parts. Only when the vehicle meets with an accident, the Caster is likely to get affected.
Fig 4.1 Positive Caster Angle
Fig 4.2 Negative Caster Angle
Included Angle:
Included Angles is the sum of Camber and Kingpin angles. It is measured and parameter given during alignment. It has left side included angle and right side included angle both must be equal other wise it must be corrected in the workshop.
Included angles = Camber angle + Kingpin angle
Toe Out on Turns:
The Turning radius of the inner wheel will be smaller than the turning radius of the outer wheel. The differenence between the turning angle of the inner wheel and the outer wheel is called Toe Out on Turns (TOOT).
Left TOOT = LT – RT / Right TOOT = RT – LT
Lock Angle:
If the steering wheel of a vehicle is turned to one side fully, it will stop at a particular point. Beyond this point, it is not possible to turn the steering wheel. The angle between GCL and the wheel plane at this point is called Lock Angle.
Ride Angle:
The distance between the lowermost part of a vehicle and the road is called the Ride Height. If the Ride height is less when the vehicle crosses short radius speed breakers or downs on a road, the vehicle lower part may touch the road causing damage.
Wheel Base and Track Width:
Track width and Wheel Base represent the overall dimensions of a vehicle and these parameters will not affect the wheel alignment but for three dimensional (3D) Wheel Alignment designer , these parameters are more important. It helps to determine the specification of the camera and lens to be used in a 3D Wheel Aligner.
Conclusion:
It is very important to maintain our vehicle angles as per the vehicle manufacturer recommendation for long duration and easy of use.
