The longer treadwear offered by modern radial tire construction can be significantly reduced by tire/axle misalignments on today's long haul vehicles. Much research has been done to demonstrate that total vehicle alignment programs pay off in the long run by extending tire life and increasing fuel economy.

As tires have increased their miles per 32nd wear potentials, the effects of poor alignment have become much more apparent. Faster wearing tires did not exhibit irregular wear in the past as much as longer running tires produced today do. Some amount of irregular wear may be unavoidable on tires that wear more slowly in line haul applications.

In the past, alignment used to mean a "front end job". Today, we understand that the steer axle is only the first part of a total alignment that involves all tire positions.

The three major front end alignment components are: Toe, Camber, and Caster

Toe is the measurement difference between tires on opposite ends of an axle. Toe is determined by the amount of distance between the front edge of the tires and the rear edge of the tires. Toe-In means the front of the tires are closer together than the rear of the tires. Toe-Out means the rear of the tires are closer together. This measurement needs to be as close to 0" as possible to make the tires run parallel to the frame of the vehicle and each other.

On tandem axle trucks and trailers with 2 or more axles, it is important that the wheels are perpendicular to the chassis centerline AND both axles are parallel to each other.

More info on large truck Tandem Axle Parallelism and Perpendicularity

Camber:

Camber is a measurement of the angle of a wheel, measured in degrees, when viewed from the front of the vehicle. If the top of the wheel is leaning out from the centerline of the vehicle then the camber is positive, if it is leaning in the camber is negative. If the camber is different on each side, it may cause the vehicle to pull to one side. Incorrect camber will result in increased wear on one side of the tire either inside or outside.

On many front wheel drive vehicles, camber is not adjustable. Problems indicate worn components instead and may need parts replaced.

Caster:

When you turn the steering wheel, the front wheels respond by turning on pivot attached to the suspension. Caster is the angle of this pivot when viewed from the side of the vehicle. When the top of the pivot is angled towards the rear, it is positive caster. Negative caster has the pivot top leaning towards the front of the vehicle.

Camber that is not adjusted properly will cause problems with straight line driving. Negative caster will cause the steering to feel light and the vehicle will wander on the road. Positive caster will cause the steering to feel heavy and the steering wheel will may kick when you hit bumps and such.

Caster has an effect on vehicle handling but little effect on tire wear.