Steering and suspension service — purpose of turning radius gauges In wheel-alignment work, turning radius gauges (turn plates) are used primarily to measure which parameter during steering checks?

Introduction / Context:
Turning radius gauges (also called turntables or turn plates) are low-friction plates placed under the front wheels during alignment. They allow precise measurement of steering angles while the suspension is loaded at ride height. This is essential for checking Ackermann geometry and maximum lock.

Given Data / Assumptions:

• Vehicle on alignment rack with turn plates under front wheels.
• Steering is centered and then turned to specified angles for measurements.
• Other alignment heads measure camber, caster, and toe.

Concept / Approach:
Turn plates have degree scales and allow smooth rotation of wheels. Technicians use them to measure inside and outside wheel steer angles, verify toe-out-on-turns, and confirm maximum steering lock against specifications. These plates are not for measuring steering wheel free play or direct toe values, which are read by alignment sensors and scales.

Step-by-Step Solution:

Verification / Alternative check:
Comparing measured angles to manufacturer toe-out-on-turns data diagnoses bent steering arms or incorrect rack position.

Why Other Options Are Wrong:

• Contact area: assessed by footprint methods, not turn plates.
• Steering free play: measured at the wheel rim or via scan-tool/angle sensor, not turn plates.
• Toe difference: measured by toe gauges or alignment heads; turn plates enable rotation but don’t directly display toe.
• Caster trail: derived from geometry; caster is measured by sweeping angles, not by turn plates alone.

Common Pitfalls:
Not zeroing plates before measurements; friction in seized plates causing erroneous readings.

Final Answer: