Wheel alignment sometimes referred to as breaking, or tracking is part of standard automobilemaintenance that consists of adjusting the angles of wheels to the car manufacturer specifications. The purpose of these adjustments is to reduce tire wear and to ensure that vehicle travel is straight and true. Alignment angles can also be altered beyond the maker's specifications to obtain a specific handling characteristic. Motorsport and off-road applications may call for angles to be adjusted well beyond normal, for a variety of reasons. An increasing number of modern vehicles have advanced driver assistance systems such as electronic stability control, anti-lock brakes, lane departure warning, adaptive cruise control and traction control. These systems can be affected by mechanical alignment adjustments. This has led many manufacturers to require electronic resets for these systems after a mechanical alignment is performed.
Primary angles
The primary angles are the basic angle alignment of the wheels relative to each other and to the car body. These adjustments are the camber, caster and toe. On some cars, not all of these can be adjusted on every wheel. These three parameters can be further categorized into front and rear. In summary, the parameters are:
Setback is the difference between right side and left side wheelbase length. It can also be measured as an angle. Setback less than the manufacturer specified tolerance does not affect car handling. That's because, when the vehicle is turning, one wheel is ahead of the other by several centimetres and therefore the setback is negligible. There are even some car models with different factory setting for right and left side wheelbase length, for various design reasons. An off-spec setback may occur because of a collision or a difference between right and left caster. Rake is the difference between the front ride heights and the rear ride heights, a positive number when the rear ride height is larger.
Measurement
A camera unit is attached to a specially designed clamp which holds on to a wheel. There are usually four camera units in a wheel alignment system. The camera units communicate their physical positioning with respect to other camera units to a central computer which calculates and displays. Often with alignment equipment, these "heads" can be a large precision reflector. In this case, the alignment "tower" contains the cameras as well as arrays of LEDs. This system flashes one array of LEDs for each reflector whilst a camera centrally located in the LED array "looks for" an image of the reflectors patterned face. These cameras perform the same function as the other style of alignment equipment, yet alleviate numerous issues prone to relocating a heavy precision camera assembly on each vehicle serviced.
Camber
Camber is the angle which the vertical axis of the wheel makes with the vertical axis of the vehicle. This angle is very important for the cornering performance of the vehicles. Generally a Camber around 0.5-2 degrees is given on the vehicles. Depending upon wheel orientation, Camber can be of three types. 1. Positive Camber The Camber would be called positive when the top of the wheels lean outwards. Positive Camber is generally used in off-road vehicles. This is because, it improves the steering response and decreases the steering efforts required for turning the vehicle. Positive Camber is also provided in load carrying vehicles. This is because the heavy load on these vehicles cause outward leaning wheels to straighten up, improving the vehicle stability. 2. Zero Camber The vehicle is said to have zero Camber when the wheels stand perfectly straight on the ground. 3. Negative Camber Negative Camber is encountered when the top of the wheels lean inwards. Providing Negative Camber improves the cornering performance. When the vehicle turns on a corner, it performs a circular motion. Hence, it experiences equal and opposite centripetal & centrifugal forces. The centripetal force is experienced in the form of friction on tyres. The centrifugal force experienced by the car tries to throw it away from the turning center. This increases the normal reaction on the outer wheels. Due to increase in normal reaction, the frictional force on the outer tyres also increase. This friction acts as centripetal force and tries to bend the outer tires inwards. The tires get deformed due to bending and the contact area between the wheels and the ground decreases. This in turns decreases the frictional force between the outer tires and the ground causing the vehicle to drift during cornering. Hence a negative Camber is given to the vehicles. The negatively cambered wheels lean inwards. So during cornering when the frictional forces try to deform the outer wheels, they just simply get flat on ground increasing the friction with road surface.
