Steering geometry — an incorrect steering axis inclination (SAI or KPI) most commonly leads to which observable vehicle behaviour on a level road, assuming other settings are nominal?

Introduction / Context:
Steering Axis Inclination (SAI), also called Kingpin Inclination (KPI), is the inward tilt of the steering pivot line when viewed from the front. Together with camber and scrub radius, SAI influences directional stability, self-centering of the steering, and steering effort. This question focuses on the practical symptom of unequal or incorrect SAI left-to-right on a roadworthy vehicle.

Given Data / Assumptions:

• Vehicle has unequal SAI between left and right sides.
• Camber, caster, and toe are assumed within normal limits, or their effects are secondary.
• Road crown is modest and cannot explain a strong pull by itself.

Concept / Approach:

SAI generates a jacking effect and contributes to the self-aligning torque via a combination of mechanical trail and camber change as the wheels steer. If one side has a smaller SAI, that wheel produces less self-centering and different camber gain, upsetting left-right lateral forces. The typical result is a persistent pull toward the side with the lesser SAI because that side develops less restoring moment and a different contact patch geometry under steer angles. While poor recovery after a turn can occur with incorrect caster or severely incorrect SAI, the asymmetric pull is the most diagnostic road symptom specifically tied to unequal SAI values.

Step-by-Step Solution:

Verification / Alternative check:

Alignment diagnostic guides list unequal SAI as a cause of vehicle pull toward the side with the smaller value. Measurement is typically via alignment machines that compute SAI during sweep tests.

Why Other Options Are Wrong:

Tendency to assume toe-out — Toe is set by track rod adjustment, not by SAI directly.
Braking effect at tight corners — More associated with excessive scrub radius or binding components.
Poor recovery after a turn — Often linked to caster deficiency or friction; SAI contributes but asymmetric pull is more definitive for incorrect SAI.

Common Pitfalls:

Blaming tyre pressure or road crown without checking SAI; attempting to correct a pull with toe adjustments rather than diagnosing underlying SAI or camber asymmetry.

Final Answer:

the vehicle to pull to the side of lesser inclination