General Knowledge · Vehicle Inspection
What is the minimum tread depth required on a steering axle (front) tire of a commercial motor vehicle?
1.2/32 inch, the depth required for tires in other axle positions
2.4/32 inch, measured at any point on a major tread grooveCorrect answer
3.6/32 inch, often treated as a stricter fleet-replacement standard
4.8/32 inch, the tread depth commonly required for a drive axle tire
Explanation
A steering axle tire must have at least 4/32 inch of tread depth measured at any point on a major tread groove, per 49 CFR 393.75(b). Steering tires get a stricter standard than tires in other positions because they carry the vehicle's steering and directional control, so less margin for worn tread is allowed there. 2/32 inch understates the requirement: that is the federal minimum for tires in other positions, not the steering axle. 6/32 inch and 8/32 inch both overstate it, since neither figure appears in the federal tread depth standard for any tire position on a commercial motor vehicle.
Source: 49 CFR 393.75(b)
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