Steering, Suspension, and Alignment
King pin inclination, alignment angles, air suspension, shock absorbers, and ride height.
- Define king pin inclination, camber, caster, and toe alignment angles
- Explain air suspension operation and the role of height control valves
- Describe shock absorber function and common spring types
- Diagnose causes of pulling, tire wear, and excessive cab bounce
Lección 1
Steering Geometry and Alignment
Alignment Angles
Proper wheel alignment is essential for tire life, fuel economy, and safe handling. Heavy trucks use the same basic alignment angles as passenger vehicles, but the geometry is adapted for heavier loads and longer wheelbases.
King pin inclination (KPI) is the inward tilt of the steering axis when viewed from the front of the vehicle. KPI provides directional stability and helps the steering return to center after a turn. It is a built-in angle that is not adjustable - if KPI is out of specification, the knuckle or axle must be replaced.
Camber is the inward or outward tilt of the wheel when viewed from the front. Positive camber means the top of the wheel tilts outward. Negative camber means the top tilts inward. Camber affects tire wear patterns - excessive negative camber or toe-out causes premature tire wear on the inside edge.
Caster is the forward or rearward tilt of the steering axis when viewed from the side. Positive caster (top of axis tilted rearward) provides directional stability and steering returnability.
Toe-In
Definition: Front of tires point inward
Purpose: Compensates for suspension play
Wear pattern: Feathered edges if excessive
Toe-Out
Definition: Front of tires point outward
Cause: Worn tie rod ends or ball joints
Wear pattern: Inside edge wear
Causes of Pulling
A truck pulls to one side when alignment is uneven. Common causes include unequal tire pressure, camber differences, or brake drag on one side. Mismatched tires (different sizes or tread depths) on the same axle also cause pulling.
Exam Tip
When the exam asks what causes a truck to pull to one side, the answer includes unequal tire pressure, camber, or brake drag. Always check the simplest things first - tire pressure - before measuring alignment angles.
King pin inclination is the inward tilt of the steering axis and is not adjustable. Toe-in means the front of the tires point inward. A truck pulls to one side due to unequal tire pressure, camber, or brake drag.