General Knowledge · Winter Driving
Under 49 CFR 393.75, what is the minimum tread depth required in a major tread groove of a commercial motor vehicle's front (steering) tires, and how does that compare to its other tires?
Explanation
Federal regulation sets a deeper minimum tread requirement for a commercial motor vehicle's front (steering) tires than for its other tires: at least 4/32 inch in a major tread groove on the front tires, compared to at least 2/32 inch on all other tires, under 49 CFR 393.75(b) and (c). The front tires get the stricter standard because they carry the steering function, and a driver who loses steering traction on a slippery surface loses the ability to control the vehicle's direction, which is why checking tread depth is part of the pre-winter vehicle check. The other options fail for a shared reason: each either reverses which tires get the stricter number, invents a uniform depth not found in the regulation, or claims federal law is silent on tread depth entirely, when in fact both figures are specifically codified.
Source: 49 CFR 393.75(b), (c)
Related Winter Driving questions
- Under 49 CFR 383.111(a)(12)(i), which weather conditions does federal regulation specifically name as examples of the "bad weather" a CDL knowledge test must cover?
- Why does guidance for driving on icy or snow-covered roads advise against using the engine brake or speed retarder?
- Which of the following is a clue that a road surface may be icy even though it does not look wet or icy?
- After driving a commercial motor vehicle through a deep puddle or standing water, why does guidance recommend applying light, steady pressure to the brakes for a short distance afterward?