Wheel alignment

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Wheel alignment on a Ford Focus 1.jpg
Wheel alignment on a Ford Focus 2.jpg
Wheel alignment on a Ford Focus 3.jpg
Wheel alignment of a Ford Focus.

Wheel alignment, which is sometimes referred to as breaking or tracking, is part of standard automobile maintenance that consists of adjusting the angles of wheels to the car manufacturer specifications. [1] The purpose of these adjustments is to reduce tire wear and to ensure that vehicle travel is straight and true (without "pulling" to one side). [2] 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.

Contents

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. [2] On some cars, not all of these can be adjusted on every wheel.

These three parameters can be further categorized into front and rear (with no caster on the rear, typically not being steered wheels). In summary, the parameters are:

Secondary angles

The secondary angles include numerous other adjustments, such as:

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 (for example, about 6mm) does not affect car handling. This is because when the vehicle is turning, one wheel is ahead of the other by several centimetres and therefore the setback is negligible. There are 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. [2]

Rake is the difference between the front and rear ride heights, a positive number when the rear ride height is larger.

Measurement

A camera unit (sometimes called a "head") is attached to a specially designed clamp which holds on to a wheel. There are usually four camera units in a wheel alignment system (a camera unit for each wheel). The camera units communicate their physical positioning with respect to other camera units to a central computer, which calculates and displays. [3]

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. [3]

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 as it improves steering response and decreases steering effort. Positive Camber is also used in load-carrying vehicles. This is because the heavy load on these vehicles causes 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 the road surface.

Signs of a bad wheel alignment

See also

Related Research Articles

Vehicle dynamics is the study of vehicle motion, e.g., how a vehicle's forward movement changes in response to driver inputs, propulsion system outputs, ambient conditions, air/surface/water conditions, etc. Vehicle dynamics is a part of engineering primarily based on classical mechanics. It may be applied for motorized vehicles, bicycles and motorcycles, aircraft, and watercraft.

<span class="mw-page-title-main">Ackermann steering geometry</span> Arrangement of steering linkages

The Ackermann steering geometry is a geometric arrangement of linkages in the steering of a car or other vehicle designed to solve the problem of wheels on the inside and outside of a turn needing to trace out circles of different radii.

<span class="mw-page-title-main">Camber angle</span> Angle between a wheels vertical axis and the vehicles vertical axis

Camber angle is one of the angles made by the wheels of a vehicle; specifically, it is the angle between the vertical axis of a wheel and the vertical axis of the vehicle when viewed from the front or rear. It is used in the creation of steering and suspension. If the top of the wheel is farther out than the bottom, it is called positive camber; if the bottom of the wheel is farther out than the top, it is called negative camber.

<span class="mw-page-title-main">Steering</span> The control of the direction of motion of vehicles and other objects

Steering is the control of the direction of motion or the components that enable its control. Steering is achieved through various arrangements, among them ailerons for airplanes, rudders for boats, tilting rotors for helicopters, and many more.

<span class="mw-page-title-main">Car suspension</span> Suspension system for a vehicle

Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two. Suspension systems must support both road holding/handling and ride quality, which are at odds with each other. The tuning of suspensions involves finding the right compromise. It is important for the suspension to keep the road wheel in contact with the road surface as much as possible, because all the road or ground forces acting on the vehicle do so through the contact patches of the tires. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear. The design of front and rear suspension of a car may be different.

<span class="mw-page-title-main">Slip angle</span> Term or maneuver in vehicle dynamics

In vehicle dynamics, slip angle or sideslip angle is the angle between the direction in which a wheel is pointing and the direction in which it is actually traveling. This slip angle results in a force, the cornering force, which is in the plane of the contact patch and perpendicular to the intersection of the contact patch and the midplane of the wheel. This cornering force increases approximately linearly for the first few degrees of slip angle, then increases non-linearly to a maximum before beginning to decrease.

Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of the vehicle to changes in steering angle associated with changes in lateral acceleration. This sensitivity is defined for a level road for a given steady state operating condition by the Society of Automotive Engineers (SAE) in document J670 and by the International Organization for Standardization (ISO) in document 8855. Whether the vehicle is understeer or oversteer depends on the rate of change of the understeer angle. The Understeer Angle is the amount of additional steering that must be added in any given steady-state maneuver beyond the Ackermann steer angle. The Ackermann Steer Angle is the steer angle at which the vehicle would travel about a curve when there is no lateral acceleration required.

Automobile handling and vehicle handling are descriptions of the way a wheeled vehicle responds and reacts to the inputs of a driver, as well as how it moves along a track or road. It is commonly judged by how a vehicle performs particularly during cornering, acceleration, and braking as well as on the vehicle's directional stability when moving in steady state condition.

<span class="mw-page-title-main">Caster</span> Undriven wheel that is designed to be attached to the bottom of a larger object

A caster is an undriven wheel that is designed to be attached to the bottom of a larger object to enable that object to be moved.

<span class="mw-page-title-main">Double wishbone suspension</span> Automotive independent suspension design

A double wishbone suspension is an independent suspension design for automobiles using two wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckle. The shock absorber and coil spring mount to the wishbones to control vertical movement. Double wishbone designs allow the engineer to carefully control the motion of the wheel throughout suspension travel, controlling such parameters as camber angle, caster angle, toe pattern, roll center height, scrub radius, scuff, and more.

<span class="mw-page-title-main">Caster angle</span> The angle between the vertical axis and the steering axis of a steered wheel, in side view

The caster angle or castor angle is the angular displacement of the steering axis from the vertical axis of a steered wheel in a car, motorcycle, bicycle, other vehicle or a vessel, as seen from the side of the vehicle. The steering axis in a car with dual ball joint suspension is an imaginary line that runs through the center of the upper ball joint to the center of the lower ball joint, or through the center of the kingpin for vehicles having a kingpin.

<span class="mw-page-title-main">Toe (automotive)</span> Installing wheels on a vehicle so that the wheels faces are not completely parallel

In automotive engineering, toe, also known as tracking, is the symmetric angle that each wheel makes with the longitudinal axis of the vehicle, as a function of static geometry, and kinematic and compliant effects. This can be contrasted with steer, which is the antisymmetric angle, i.e. both wheels point to the left or right, in parallel (roughly). Negative toe, or toe out, is the front of the wheel pointing away from the centreline of the vehicle. Positive toe, or toe in, is the front of the wheel pointing towards the centreline of the vehicle. Historically, and still commonly in the United States, toe was specified as the linear difference of the distance between the two front-facing and rear-facing tire centerlines at the outer diameter and axle-height; since the toe angle in that case depends on the tire diameter, the linear dimension toe specification for a particular vehicle is for specified tires.

<span class="mw-page-title-main">Beam axle</span> Automobile mechanism

A beam axle, rigid axle or solid axle is a dependent suspension design in which a set of wheels is connected laterally by a single beam or shaft. Beam axles were once commonly used at the rear wheels of a vehicle, but historically they have also been used as front axles in four-wheel-drive vehicles. In most automobiles, beam axles have been replaced with front (IFS) and rear independent suspensions (IRS).

<span class="mw-page-title-main">Ball joint</span> Spherical bearing most commonly used in automobile steering mechanisms

In an automobile, ball joints are spherical bearings that connect the control arms to the steering knuckles, and are used on virtually every automobile made. They bionically resemble the ball-and-socket joints found in most tetrapod animals.

<span class="mw-page-title-main">Bicycle and motorcycle dynamics</span> Science behind the motion of bicycles and motorcycles

Bicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles and their components, due to the forces acting on them. Dynamics falls under a branch of physics known as classical mechanics. Bike motions of interest include balancing, steering, braking, accelerating, suspension activation, and vibration. The study of these motions began in the late 19th century and continues today.

The scrub radius is the distance in front view between the king pin axis and the center of the contact patch of the wheel, where both would theoretically touch the road. It can be positive, negative or zero.

<span class="mw-page-title-main">Bump steer</span>

Bump steer is the term for the tendency of the wheel of a car to steer itself as it moves through the suspension stroke.

<span class="mw-page-title-main">Twist-beam rear suspension</span> Type of automobile suspension

The twist-beam rear suspension is a type of automobile suspension based on a large H- or C-shaped member. The front of the H attaches to the body via rubber bushings, and the rear of the H carries each stub-axle assembly, on each side of the car. The cross beam of the H holds the two trailing arms together, and provides the roll stiffness of the suspension, by twisting as the two trailing arms move vertically, relative to each other.

<span class="mw-page-title-main">Camber thrust</span>

Camber thrust and camber force are terms used to describe the force generated perpendicular to the direction of travel of a rolling tire due to its camber angle and finite contact patch. Camber thrust is generated when a point on the outer surface of a leaned and rotating tire, that would normally follow a path that is elliptical when projected onto the ground, is forced to follow a straight path while coming in contact with the ground, due to friction. This deviation towards the direction of the lean causes a deformation in the tire tread and carcass that is transmitted to the vehicle as a force in the direction of the lean.

<span class="mw-page-title-main">Stance (vehicle)</span> Auto term for positioning of a vehicle

The stance of a vehicle is determined by its suspension height and the fitment of the wheels in the fender arches. It may refer to any vehicle, including sports cars, pickup trucks and off-road vehicles, however it is mostly associated with lowered sports cars, sedans, hatchbacks, vans and other body styles of passenger cars. The term stance is most commonly associated with the stanced car subculture, a style of modifying cars which emphasizes lowering cars, typically with either coilovers or air suspension, and often adding negative camber to the wheels to achieve the "stanced" look. The main parameters of the vehicle's stance are suspension height and position of the wheels. Suspension height usually depends on the suspension components while wheel position usually depends on the rim size and offset. Tire fitment also plays a big role from both visual and functional perspective.

References

  1. "Wheel Alignment - YourNewTyres" . Retrieved 2020-06-14.
  2. 1 2 3 "Wheel Alignment A Short Course - CarParts.com" . Retrieved 11 March 2017.
  3. 1 2 "Things to consider when choosing an aligner | Pro-Align". Pro-Align. Retrieved 2017-11-27.