What is the minimum tire tread depth required on the steering axle of a commercial motor vehicle?

49 CFR 393.75 (tires); AAMVA CDL Manual Sec. 2.1.3, p.2-1

Steering tires need deeper tread than other positions because they are responsible for directional control and are more susceptible to hydroplaning. The 4/32-inch versus 2/32-inch distinction between steering and other axles is a frequently tested detail that also matters for real pre-trip inspections and avoiding out-of-service citations.