Major Tread Grooves

A question recently came up in regards to the enforcement of FMCSR 393.75 in relation to tire tread depth. It was pointed out that different language is used to describe when a violation occurs. The differences caused questions to arise as to the intent of paragraph (c). There have also been questions arise from the term \"major tread groove\" used in the section. 393.75(b) Any tire on the front wheels of a bus, truck, or truck tractor shall have a tread groove pattern depth of at least 4/32 of an inch when measured at any point on a major tread groove. (c) Except as provided in paragraph (b) of this section, tires shall have a tread groove pattern depth of at least 2/32 of an inch when measured in a major tread groove.

Having the same language describing when a violation occurs will promote uniformity and proper enforcement of each paragraph in the section. Adding the definition of a major tread groove to the FMCSR's would assist roadside inspectors in the event the question would arise as to where the tread depth is to be measured. The only place to find this information currently is in the NAS Level I course material in module 1 page 1-13.

I request that if the committee finds the need, that CVSA petition FMCSA to modify the language in paragraph (c) to match that in paragraph (b) to describe when a violation of minimum tread depth occurs. In regards to the \"major tread groove\" definition, I request the same action to be initiated if the committee agrees. The definition in the NAS Level I course could be used after consultation with the manufacturers. Major Tread Groove - molded through the complete thickness of tread rubber and are the deepest grooves made by the manufacturer (any groove containing a tread wear indicator).(c) Except as provided in paragraph (b) of this section, tires shall have a tread groove pattern depth of at least 2/32 of an inch when measured at any point on a major tread groove.