Tracking / Camber / Caster
It's important that all axles are aligned with the truck's front axles. Misalignment of drive and trailer axles causes excessive treadwear on the leading edge of the steer, drive and trailer tires. If continual turning of the drive tires is necessary in order to maintain a straight course, check the tracking on the vehicle's wheel alignment.
Camber is the measure of the tilt of the top of a wheel or tire either toward the vehicle or away from it. Wheel alignment is in a positive camber when a tire tilts away from the vehicle, causing premature treadwear along the tire's outside shoulder.
When a tire tilts toward the vehicle, the tire is experiencing negative camber, thus it wears away at the inside shoulder of the tire. In a tractor-trailer combination, the drive tires traditionally experience positive camber, while the trailer tires are in negative camber.
Toe-in and toe-out, improper tracking and positive or negative camber all affect tire treadwear. Be sure to address each wheel alignment setting before tire treadwear becomes excessive, otherwise, your tire performance may be permanently affected.
Two additional settings, caster and kingpin inclination (KPI), determine whether or not a vehicle is in complete alignment. Adjustments in caster and KPI are usually associated with handling problems and steering instability, not tire wear problems.
Caster is the forward or backward tilt of the top of the kingpin in a wheel assembly. Correct kingpin positioning may be either completely vertical or slightly inclined inward. In a condition of positive caster, the top of the kingpin tilts backwards toward the rear of the car.
A wheel experiences negative caster when the kingpin tilts forward. Again, adjustments in caster affect steering and handling. However, if a caster problem is ignored or incorrectly adjusted, it may result in irregular treadwear.