Wheel alignment should be checked whenever new tyres are installed, suspension components installed, when the vehicle has encountered a major road hazard or curb and any time unusual tyre wear patterns appear.
Wheel alignment is the measurement of complex suspension angles and the adjustment of a variety of suspension components. It is a suspension-tuning tool which greatly influences the vehicle's handling and tyre wear.
Wheel alignment consists of adjusting the angles of the wheels so that they are parallel to each other and perpendicular to the ground, thus maximizing tyre life and ensures straight and true tracking along a straight and level road.
The primary static suspension angles that need to be measured and adjusted are caster, camber, toe and thrust angle.
The following are definitions Conditions and Possible Causes of each angle and its influence on a vehicle and its tyres.
Camber is the angle of the wheel, measured in degrees, if the top of the wheel is tilted out then the camber is positive, if it's tilted in, then the camber is negative.
If the camber is out of adjustment, it will cause premature tyre wear on one side of the tyre's tread. When the camber is out of adjustment it can cause a pulling problem to the side with the more positive camber.
This usually happens when the vehicle has been involved in an accident which has caused structural damage or damage to the strut and / or spindle assembly. Camber also goes out of adjustment when the springs sag and causes ride height to change, or when ball joints and or other attached parts are worn or defective. It also varies depending on speed as aerodynamic forces changes riding height.
After repair and alignment, pulling problem could persist due to the insufficient and or uneven tyre to road contact. If a tyre shows camber wear pattern, moving it to the rear might be effective but replacement might be best.
Whenever camber changes, it directly affects toe.
On most front-wheel-drive vehicles, camber is not adjustable, however there are aftermarket kits that allow sufficient adjustment to compensate for accident damage or the change in alignment due to the installation of lowering springs.
Caster is the angle of the steering pivot, measured in degrees.
Viewed from the side, the caster is the tilt of the steering axis. When the wheel is in front of the load the caster is positive. Three to five degrees of positive caster is the typical range of settings, with lower angles are being used on heavier vehicles to reduce steering effort.
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. If the caster is equal but too positive, the steering will be heavy and the steering wheel may kick when you hit a bump.
One of the best ways to visualize caster is to picture the caster on a shopping cart. The pivot while not at an angle intersects the ground ahead of the wheel contact patch. When the wheel is behind the pivot at the point where it contacts the ground, it is in positive caster.
Like camber, on many front-wheel-drive vehicles, caster is not adjustable. If the caster is out of adjustment on these vehicles, it indicates that something is possibly bent from an accident, and must be repaired or replaced.
Toe setting is the most critical alignment settings relative to tyre wear. if the toe setting is just 0.8mm off of its appropriate setting, each tyre on that axle will scrub almost 3 1/2 feet sideways every mile, therefore reducing tyre life.
Like camber, toe will change depending on vehicle speed, as aerodynamic forces changes the riding height hence affecting camber and toe due to the geometry of the steering linkage in relation to the geometry of the suspension.
The toe angle identifies the direction of the tyres compared to the centerline of the vehicle. Rear-wheel drive vehicle "pushes" the front tyres, as they roll along the road, resistance causes some drag resulting in rearward movement of the suspension arms against their bushings. Most rear-wheel drive vehicles use positive toe to compensate for suspension movement.
Front-wheel drive vehicle "pulls" the vehicle, resulting in forward movement of the suspension arms against their bushings.
Toe can also be used to alter a vehicle's handling traits. Increased toe-in will reduce oversteer, steady the car and enhance high-speed stability.
Increased toe-out will reduce understeer, free up the car, especially during initial turn-in while entering a corner.
Before adjusting toe outside the vehicle manufacturer's specification to manipulate handling, be aware that toe setting influences tyre wear. Excessive toe settings often causes drivability problems, especially during heavy rain. This is because most highways have tyre groves from the daily use by loaded trailers. These heavy vehicles leave groves that fill with water. When one of the vehicles front tyre encounters a puddle, it loses some of its grip, the other tyre's toe setting will push causing excessive toe-in, or pull causing excessive toe-out. This may cause the vehicle to feel unstable.
Thrust angle is the direction that the rear wheels are pointing in relation to the centerline of the vehicle.
The vehicle will "crab" if the thrust angle is not zero and the steering wheel will not be centered.
The best solution is to first adjust the rear toe to the centerline and then adjust the front toe. This is done during a all wheel alignment if the rear toe is adjustable. If the rear is not adjustable, then the front toe must be set to compensate for the thrust angle, allowing the steering to be centered.
If the thrust angle is not correct on a vehicle with a solid rear axle, it often requires a frame straightening shop to correctly reposition the rear axle.
A vehicles with independent rear suspension, the toe must be adjusted individually until it has reached the appropriate setting for its side of the vehicle, incorrect thrust angle is often caused by an out-of-position suspension or incorrect toe settings.
So in addition to the handling problems that are the result of incorrect toe settings, thrust angles can also cause the vehicle to handle differently when turning left vs. right.
Steering center is that the steering wheel is centered when the vehicle is traveling down a straight and level road. However most roads are crowned to allow for water drainage, this may cause the vehicle to drift to the left so the steering wheel will appear to be off-center to the left on a straight road. to compensate for this
· The left caster should be more positive than the right, but not more than 1/2 degree within the specified range.
· The left camber should be more negative than the right camber. Check the specs to see what the allowable differences.
A crooked steering wheel is one of the most common complaints after a wheel alignment. 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. the steering wheel is then locked in a straight-ahead position in order to set the front toe. Please note; before locking the steering wheel, the engine should be started and the wheel turned right and left a couple of times. This will take any stress off the power steering valve. Repeat the above starting and turning of the steering after setting front toe to ensure that the steering valve wasn't loaded again due to the tie rod adjustments.