In car terminology, wheel alignment refers to the alignment of the wheel in reference to its relationship between the car and the road. Each car has a recommended wheel alignment to ensure that the vehicle runs straight. In some cases, this can be changed for specific purposes, such as in various forms of auto racing. Here, cornering at high speed might demand a different wheel alignment than is needed to drive at lower speeds on straight roads.
There is a specific car terminology used with respect to wheel alignment. Here is an explanation of the most important of the terms used.
It is well known that the camber of a road is its angle from center to the curb. Corners tend to have a camber to help prevent cars drifting out to the left when cornering – or to the right in the UK, Australia, Japan and other countries that drive on the left.
With respect a wheel, the camber is the angle of the wheel. If you look at the front of a car, if the top of a wheel leans out from the body it is known as a positive camber. Leaning into the body is a negative camber. Either of these two will naturally cause uneven wear on the tire.
Many believe that a negative camber looks cool, and it certainly offers more grip when cornering. The down side is less grip on straight roads because there is less contact surface between the tire and the road. That is not the only negative of negative camber! The other is camber thrust.
When opposing wheels have negative camber, the tires are pushing against each other. No problem if both tires are in contact with the ground. However if one tire leaves the ground, the thrust is to that side and the vehicle becomes difficult to handle. It tends to slide away from the wheel that is in contact with the ground.
When racing round an oval at high speed with negative camber on the tires, centrifugal force can cause the outside tire to leave the surface. The inside tire has no opposing force, so pushes the car to the outside and into the barrier.
The Best Wheel Camber?
The preferred camber for a tire on a normal domestic vehicle is zero – meaning dead straight down in relation to the axle of the car. The weight of the vehicle is supported by the center of the tire rather than by one side or the other. This is the way most tires are designed – to sit straight down with no camber.
However, you lose performance when cornering, and in races on ovals or where there is a high degree of cornering involved, the wheel camber will be adjusted to suit the needs of the driver. In most cars it is possible to adjust the camber. However, there are certain cars where the camber cannot be adjusted. It is intended to be straight at all times.
This is particularly true of certain front wheel drive vehicles. If the camber is positive or negative, then there is a problem with the suspension that requires attention. Although zero camber will ultimately lead to more tire wear, it will be even. Because cambered wheels wear tires at one side, their life can be extended by regularly switching right and left tires around.
Unlike camber, wheel caster is a difficult concept to visualize. It refers to the pivot point of the steering in relation to the front and back of the car. When you turn the steering wheel, the front wheels turn a pivot attached to the suspension. The position of this pivot can affect the car’s tracking.
If the top of the line of the pivot lies back towards the back of the car, this is known as positive caster. This will make your vehicle handle better at high speeds and increase the lean of the tire when cornering offering more grip.
Most production cars are fitted with ‘cross-caster’ which is a safety arrangement designed to create a difference between the caster and camber. The result of this is to make your car run to the right when rolling free, so that it runs right towards the curb rather than left into traffic. If you lose your steering, or a vehicle is left with the brake off, it bears right away from oncoming traffic.
The toe of your wheels is a measurement of the relative horizontal distance between your front and back tires. If your tires are ‘toe-in’ it means that if you park tight against a wall, your back tire will be closer to the wall than the front whether the wall is to your right or left. The opposite is true of ‘toe-out.’
The ideal condition is that your tires are in an equal position front to back, forming a rectangle if they were connected by lines. If there is any toe on a car, the car will be less stable than it should be. The toe is adjustable on all cars, so have it checked during your regular services.