Veh. Code, § 27465

(a) No dealer or person holding a retail seller’s permit shall sell, offer for sale, expose for sale, or install on a vehicle axle for use on a highway, a pneumatic tire when the tire has less than the tread depth specified in subdivision (b). This subdivision does not apply to any person who installs on a vehicle, as part of an emergency service rendered to a disabled vehicle upon a highway, a spare tire with which the disabled vehicle was equipped.

(b) No person shall use on a highway a pneumatic tire on a vehicle axle when the tire has less than the following tread depth, except when temporarily installed on a disabled vehicle as specified in subdivision (a):

(1) One thirty-second (1/32) of an inch tread depth in any two adjacent grooves at any location of the tire, except as provided in paragraphs (2) and (3).

(2) Four thirty-second (4/32) of an inch tread depth at all points in all major grooves on a tire on the steering axle of any motor vehicle specified in Section 34500, and two thirty-second (2/32) of an inch tread depth at all points in all major grooves on all other tires on the axles of these vehicles.

(3) Six thirty-second (6/32) of an inch tread depth at all points in all major grooves on snow tires used in lieu of tire traction devices in posted tire traction device control areas.

(c) The measurement of tread depth shall not be made where tie bars, humps, or fillets are located.

(d) The requirements of this section shall not apply to implements of husbandry.

(e) The department, if it determines that such action is appropriate and in keeping with reasonable safety requirements, may adopt regulations establishing more stringent tread depth requirements than those specified in this section for those vehicles defined in Sections 322 and 545, and may adopt regulations establishing tread depth requirements different from those specified in this section for those vehicles listed in Section 34500.