Proper alignment is an important factor in lowering operational costs. Ideally, when a truck is traveling in a straight line, all of the axles are parallel—and perpendicular to the vehicle centerline—and all the tires are rolling in a straight line, too. Not only will tires on a properly aligned vehicle last longer, but some manufacturers suggest that there are significant improvements in fuel economy, component wear, and even driver fatigue.
It is universally know that alignment plays as critical a role in vehicle efficiency as does any other factor. Still, between 70 and 80 percent of commercial vehicles on the road today are misaligned! Maintaining proper alignment settings is an arduous task, but it’s one that will be rewarded by your bottom line.
Most alignment issues can be attributed to one of four factors:
- Ackerman angle
- Caster/camber settings
- Toe settings
- Axle alignment
Ackerman steering geometry is an arrangement of linkages in the steering of a vehicle designed to solve the problem of wheels on the inside and outside of a turn needing to trace out circles of a different radius. The intention of Ackerman geometry is to avoid the need for tires to slip sideways when following the path around a curve.
Incorrect Ackerman geometry generally scuffs the tires when driving through corners and might cause tire squeal during sharp turns. The Ackerman angle should be checked as part of any routine wheel alignment, on new vehicles and when a vehicle’s wheelbase is modified or exhibits toe-type wear despite a proper toe-in setting.
The inside wheel turns in more sharply than the outside wheel.
Caster is the forward or rearward tilt of the steering’s pivot point line in reference to a vertical line. Caster is positive if the line is angled toward the vehicle’s rear, and negative if the tilt is forward. Typically, 2 to 5 degrees of positive caster is recommended to make the vehicle more stable at high speeds and improve handling.
Camber angle is the measure in degrees of the difference between the wheel’s vertical alignment perpendicular to the surface. If a wheel is perfectly perpendicular to the surface, its camber would be 0 degrees. Camber is negative when the tops of the tires tilt inward (towards the vehicle) and positive when the top of the tire tilts away. On newer trucks, camber wear should not be a major issue. Most trucks leave the factory with zero to slightly positive camber. Excessive positive camber will result in excessive shoulder wear, while negative camber will wear the inner half of your tire. Correcting camber settings requires a bending of the front axle (which voids most manufacturer warranties). If an alignment shop indicated that camber is out of spec, the vehicle’s front bearing should be checked.
POSITIVE CAMBER WHEEL IS TILTED OUTWARD AT THE TOP
NEGATIVE CAMBER WHEEL IS TILTED INWARD AT THE TOP
The toe angle identifies the direction of the tires compared to the centerline of the vehicle. It is expressed in either degrees or fractions-of-an-inch, and an axle is said to have “positive toe-in” when the imaginary lines created by the tires intersect in front of the vehicle and “ negative toe-out” if they diverge. When drive tires propel a vehicle with improper toe settings forward, there is an increase in rolling resistance that negatively impacts fuel-efficiency, ride comfort, and ultimately shortens the life of your tires. The vehicle’s toe is the most critical alignment settings relative to tire wear. If the toe setting is just 1/32" off of its appropriate setting, each tire on that axle will scrub almost 3 1/2 feet sideways every mile, significantly reducing tire life.
TOE-IN IS THE MOST BASIC FRONT-END SETTING.
Typically toe is set at 1/16" toe-in (+ 1/16"). Measured and set in a static state, toe-in allows the wheels to run straight, when the vehicle is loaded rolling down the highway.
TOE-IN: The distance between the front of the tires is less than the distance between the rear of the tires.
TOE-OUT: The distance between the front of the tires is greater than the distance between the rear of the tires.
MISALIGNED DRIVE AXLES
Generally when you think about the benefits of a properly aligned vehicle, you think about lowering operating costs via longer tire life – but that’s only the beginning. Not only will proper alignment extend tire life, but it has also shown to improve fuel economy, component wear and even driver fatigue.
Vehicle alignment isn’t a matter of just aligning the steer axle. It means aligning the drive and trailing axles, too. In a perfect world, trucks would travel in perfectly straight lines from one location to another. If this were the case, as the truck went down the road the axles would remain parallel, perfectly perpendicular to the vehicle centerline, and worries about tire life would be a thing of the past. Unfortunately, driving forces, mechanical complications, and other issues can cause axles to fall out of alignment, negatively impacting wear.
STANDARD RIGHT THRUST
Cause: Occurs if the vehicle’s drive axles are pushing the truck to the right.
Result: Wear on the right steer tire will mimic toe-out wear while the left side will exhibit the feathering on the right shoulder associated with toe-in alignment.
STANDARD LEFT THRUST
Cause: Occurs if the vehicle’s drive axles are pushing the truck to the left.
Result: Wear on the left steer tire will mimic toe-in wear while the right side will exhibit toe-out wear.
RIGHT THRUST - TOE-IN
Cause: There are also combinations of both toe and axle misalignment, which will put stress on just one steer tire.
Result: Here, the toe-in setting combined with right thrust misalignment causes the left front to wear normally while the right front feel like toe-in.
RIGHT THRUST - TOE-OUT
Cause: On the other hand, toe-out combined with right thrust will cause the front right to wear normally but places stress on the left.
Result: Standard wear on the right side with wear resembling toe-out.