After completing a regional delivery run, a tractor-trailer driver performs the mandatory … — Commercial Driver's License (CDL) General Knowledge Exam

After completing a regional delivery run, a tractor-trailer driver performs the mandatory post-trip examination across the vehicle's key mechanical and safety assemblies to prepare the daily condition report. Which detected condition represents an active safety defect that must be officially documented and corrected before the combination can be driven again?

A
A steering assembly on a twenty-inch wheel that demonstrates approximately 1.25 inches of free play before engaging the steering gear
B
An S-cam foundation brake slack adjuster that travels 0.75 inch when pulled firmly by hand with the parking brakes released
A steering-axle tire displaying a remaining tread depth of 3/32 inch measured in a major tread grooveAnswer
D
An emergency storage compartment containing three bi-directional red reflective triangles, spare electrical fuses, and a properly rated 10 B:C fire extinguisher

Answer

A steering-axle tire displaying a remaining tread depth of 3/32 inch measured in a major tread groove

Federal safety regulations mandate that front steer-axle tires must have at least 4/32 inch of tread depth in every major groove. A steer tire worn down to 3/32 inch is illegal to operate, poses a significant hydroplaning and steering hazard, and must be logged on the post-trip DVIR for replacement before the vehicle is operated again.

Step-by-Step Solution

Evaluate federal commercial motor vehicle safety standards for tire tread depth across different axle positions

Steering-axle tires require a minimum tread depth of

4/32\text{ inch}

(

1/8\text{ inch}

) in every major groove, whereas all other tires (drive and trailer) require a minimum of

2/32\text{ inch}

(

1/16\text{ inch}

Steer tires are vital for directional control and hydroplaning resistance, requiring double the minimum tread depth of non-steer tires.

Assess the remaining inspection options against federal safety and out-of-service tolerances

Steering wheel play under 2 inches on a 20-inch wheel, brake pushrod travel under 1 inch upon manual pull, and an emergency kit with 3 reflective triangles plus spare fuses all meet compliance criteria.

These measurements and equipment configurations fall strictly within permissible manufacturer and regulatory operating tolerances.

Identify the non-compliant condition requiring mandatory DVIR documentation and repair

A steer tire with

3/32\text{ inch}

of tread is below the

4/32\text{ inch}

threshold and represents a critical safety violation.

Any deficiency affecting safe vehicle operation must be documented on the post-trip Driver Vehicle Inspection Report (DVIR) and rectified prior to redispatch.

Key Concept

Critical Mechanical Tolerances in En-Route and Post-Trip Inspections

Estimated Time:1m 30s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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