Alignments

Wheel Alignment

Wheel Alignment sometimes referred to as tracking, is part of standard vehicle maintenance that consists of adjusting the angles of the wheels so that they are set to the car maker’s specification. 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).

In its most basic form, a wheel alignment consists of adjusting the angles of the wheels so that they are perpendicular to the ground and parallel to each other. The purpose of these adjustments is maximum tire life and to allow the vehicle to track straight and true when driving along a straight and level road. If the alignment is out, it can cause excessive tire wear and steering or tracking problems.

Worn steering, suspension and drive line components can cause noise, vibration, premature tire wear and misalignment. That is why F & F Tire performs a complete steering and suspension system inspection with every alignment.  By replacing worn parts, you regain steering control and handling which will return your vehicle to its original operating performance.

Four-Wheel Alignments

This type of alignment is a full 4-wheel alignment where the adjustments are first made to true up the rear alignment, then the front is adjusted. A full 4-wheel alignment will cost more than the other type because there is more work involved.. 

Pulling problems are not always related to wheel alignment.  Problems with tires (especially unequal air pressure), brakes and power steering can also be responsible. It is up to a good wheel alignment technician to determine the cause.

The key parts that affect alignments are: ball joints, bushings, sway bar links, center links, idler arms/pitman arms, rack and pinion units, tie rod ends/sleeves, shock absorbers, struts/cartridges and coil springs.

If you know anything about wheel alignment, you’ve probably heard the terms
Caster, Camber and Toe-in

Caster

Caster is the tilting of the uppermost point of the steering axis either forward or backward (when viewed from the side of the vehicle). If the top of the pivot is leaning toward the rear of the car, then the caster is positive, if it is leaning toward the front, it is negative. If the caster is out of adjustment, it can cause problems in straight line tracking. If the caster is different from side to side, the vehicle will pull to the side with the less positive caster. If the caster is equal but too negative, the steering will be light and the vehicle will wander and be difficult to keep in a straight line, steering may be touchy at high speed and wheel return ability may be diminished when coming out of a turn. If the caster is equal but too positive, the steering will be heavy and the steering wheel may kick when you hit a bump. Caster has little affect on tire wear.

Caster is affected by the vehicle height, therefore it is important to keep the body at its designed height. Overloading the vehicle or weak / sagging springs will affect caster. When the rear of the vehicle is lower than its designated trim height, the front suspension moves to a more positive caster. If the rear of the vehicle is higher than its designated trim height, the front suspension moves to a less positive caster.

Wheel Alignment


Camber

 Wheel Alignment

Camber is the tilting angle of the wheel, measured in degrees, when viewed from the front of the vehicle. When the wheels tilt outward at the top, the camber is positive (+). When the wheel tilts inward at the top, the camber is negative (-). The amount of tilt is measured in degrees from the vertical. Camber settings influence the directional control and the tire wear.

 If the camber is out of adjustment, it will cause tire wear on one side of the tire’s tread. Too much positive camber will result in premature wear on the outside of the tire and cause excessive wear on the suspension parts. Too much negative camber will result in premature wear on the inside of the tire and cause excessive wear on the suspension parts.

Unequal side-to-side camber of 1° or more will cause the vehicle to pull or lead to the side with the most positive camber.

Wheel Alignment
Camber wear pattern

On many front-wheel-drive vehicles, camber is not adjustable. If the camber is out on these cars, it indicates that something is worn or bent, possibly from an accident and must be repaired or replaced.

On many vehicles, camber changes with different road speeds. This is because aerodynamic forces cause a change in riding height from the height of a vehicle at rest. Because of this, riding height should be checked and problems corrected before setting camber. Camber specs are set so that when a vehicle is at highway speed, the camber is at the optimal setting for minimum tire wear.

For many years the trend has been to set the camber from zero to slightly positive to offset vehicle loading, however the current trend is to slightly negative settings to increase vehicle stability and improve handling.

Toe-in

Wheel Alignment 

Toe is a measurement of how much the front and/or rear wheels are turned in or out from a straight-  ahead position. When the wheels are turned in, toe is positive (+). When the wheels are turned out, toe is negative (-). The actual amount of toe is normally only a fraction of a degree. The purpose of toe is to ensure that the wheels roll parallel. Toe also serves to offset the small deflections of the wheel support system that occur when the vehicle is rolling forward. In other words, with the vehicle standing still and the wheels set with toe-in, the wheels tend to roll parallel on the road when the vehicle is moving. Improper toe adjustment will cause premature tire wear and cause steering instability

. An incorrect toe-in will cause rapid tire wear to both tires equally. This type of tire wear is called a saw-tooth wear pattern as shown in this illustration.

TOE WEAR

Wheel Alignment

If the sharp edges of the tread sections are pointing to the center of the car, then there is too much toe-in. If they are pointed to the outside of the car then there is too much toe-out. Toe is always adjustable on the front wheels and on some cars, is also adjustable for the rear wheels.

Like camber, toe will change depending on vehicle speed. As aerodynamic forces change the riding height, the toe setting may change due to the geometry of the steering linkage in relation to the geometry of the suspension.

Thrust Angle

Wheel Alignment

Thrust angle is the direction that the rear wheels are pointing in relation to the center line of the vehicle  If the thrust line is to the right of the centerline, the angle is said to be positive. If the thrust line is to the left of center, the angle is negative. . If the thrust angle is not zero, then the vehicle will “dog track” and the steering wheel will not be centered.  It is caused by rear wheel or axle misalignment and causes the steering to pull or lead to one side or the other. It is the primary cause of an off-center or crooked steering wheel. Correcting rear axle or toe alignment is necessary to eliminate the thrust angle. If that is not possible, using the thrust angle as a reference line for aligning front toe can restore center steering.

Steering Axis Inclination (SAI)

Wheel Alignment

SAI is the angle formed by a line that runs through the upper and lower steering pivots with respect to vertical. On a SLA suspension, the line runs through the upper and lower ball joints. On a MacPherson strut suspension, the line runs through the lower ball joint and upper strut mount or bearing plate. Viewed from the front, SAI is also the inward tilt of the steering axis. Like caster, it provides directional stability. But it also reduces steering effort by reducing the scrub radius. SAI is a built-in nonadjustable angle and is used with camber and the included angle to diagnose bent spindles, strutsand mislocated crossmembers.

This angle, when added to the camber to form the included angle causes the vehicle to lift slightly when you turn the wheel away from a straight ahead position. This action uses the weight of the vehicle to cause the steering wheel to return to the center when you let go of it after making a turn. Because of this, if the SAI is different from side to side, it will cause a pull at very slow speeds.

Riding Height

Wheel Alignment

Ride height is the distance between a specified point on the chassis, suspension or body and the ground. Measuring ride height is an indirect method of determining spring height, which is important because it affects camber, caster and toe. Low ride height indicates weak or sagging springs. Ride height should be within specifications before the wheels are aligned.

 

Wheel alignment charts provide specs, but the main thing is that the measurements should be within one inch from side to side and front to rear. Riding height is not adjustable except on vehicles with torsion bar type springs.  The best way to fix this problem is to replace the springs (Note: springs should only be replaced in matched pairs). Changes in riding height will affect camber and toe so if springs are replaced or torsion bars are adjusted, then the wheel alignment must be checked to avoid the possibility of tire wear.

Steering Center

Wheel Alignment

Steering center is simply the fact that the steering wheel is centered when the vehicle is traveling down a straight and level road. A crooked steering wheel is usually the most common complaint that a customer has after a wheel alignment is performed. Assuming that the steering wheel stays in the same position when you let go of the wheel (in other words, the car is not pulling), then steering center is controlled by the front and rear toe settings. When setting steering center, the rear toe should be set first bringing the Thrust Angle as close to the vehicle centerline as possible. Then the steering wheel is locked in a straight ahead position while the front toe is set.

Another problem with steering center has to do with the type of roads that are driven on. Most roads are crowned to allow for water drainage, you usually drive on the right side of the crown. This may cause the vehicle to drift to the right so that the steering wheel will appear to be off-center to the left on a straight road.