Arizona Studded Tires: Legal October 1 to May 1

Arizona treats studded tires as an equipment question rather than a winter-driving question. The rule is A.R.S. § 28-958, headed "Tire equipment restrictions", which sits in Title 28, Chapter 3, Article 16 alongside the state's lamp, brake and mirror requirements. Subsection B opens with a flat prohibition: a tire moved on a highway may not carry on its periphery "any block, stud, flange, cleat, spike or other protuberance" made of anything other than rubber and projecting beyond the tread of the traction surface. Studded snow tires are legal only because paragraph 3 of that subsection carves them back out.

The carve-out is a fixed calendar window: "From October 1 to May 1". Nothing in the section ties it to elevation, to a snow zone, to a declared storm or to a posted advisory, so it runs identically in Flagstaff, Show Low, Payson, Alpine and Pinetop as it does in Phoenix, Tucson and Yuma. A driver in the northern high country may fit studs on October 1 without waiting for the first storm on the Mogollon Rim or over Interstate 17 at Sunset Point, and a driver in the Sonoran Desert may legally run them in January even though there is no practical reason to. The flip side is that the window is not extended for a late spring at 7,000 feet: studs come off for May through September regardless of what the San Francisco Peaks are doing.

Paragraph 3 also regulates the studs themselves, and it does so by contact area rather than by count. The tire must be pneumatic, the studs must be "metal type studs of tungsten carbide or other suitable material", and they must be inserted or constructed so that "the number of studs or the percentage of metal in contact with the roadway does not exceed three per cent of the total tire area in contact with the roadway under any conditions". Arizona names no maximum stud count and no projection height, so a factory-studded winter tire sold for northern-state use is the safe way to satisfy the three per cent test; a home-studded tire is the driver's own problem to prove.

Tire chains are handled by a different paragraph and on different terms. A.R.S. § 28-958(B)(2) permits "tire chains of reasonable proportions on a vehicle when required for safety because of snow, ice or other conditions tending to cause a vehicle to skid". There is no date attached, so chains are lawful in October or in May, but the permission is conditional on the conditions actually calling for them rather than on the calendar. The remaining exceptions in subsection B and C are agricultural: farm machinery with protuberances "that will not injure the highway" is exempt outright, and the ADOT director and local authorities within their own jurisdictions may issue special permits for traction engines or tractors with movable tracks and transverse corrugations, and for farm tractors and other farm machinery that could not otherwise use a highway. Subsection A carries an older rule for solid rubber tires, which must have rubber at least one inch thick above the edge of the flange across the entire traction surface.

The duty is not only the driver's. A.R.S. § 28-921(A) makes it unlawful to drive or move, and makes it unlawful for an owner to knowingly cause or permit to be driven or moved, a vehicle that "is equipped in any manner in violation of this article". The only vehicles Article 16 releases from its equipment rules are farm trailers hauling unprocessed fiber, road machinery, road rollers, farm tractors and implements of husbandry being incidentally moved, plus Arizona Game and Fish Department vehicles on night poaching patrols. There is no exemption for out-of-state plates, so a vehicle driven down from Utah, Colorado or New Mexico in June is subject to the same May 1 deadline as an Arizona-registered one.

Separately, A.R.S. § 28-1106(A) lets a local authority prohibit vehicle operation or restrict vehicle weights on its own highways, by ordinance or resolution and for not more than ninety days in any one calendar year, where the highway "by reason of deterioration, rain, snow or other climatic conditions will be seriously damaged or destroyed" otherwise. Subsection B makes such an ordinance ineffective until signs are erected and maintained at each end of the affected stretch, and subsection D gives the ADOT director the same power over state highways. That is the mechanism behind a seasonal closure or weight posting on a mountain road, and it is separate from the studded-tire window.

§ 28-958 by way of § 28-921(A), and it is not a crime. § 28-121(A) makes a Title 28 violation a class 2 misdemeanor by default but expressly disapplies that default to Chapter 3, where § 28-958 sits; § 28-121(B) then classifies the violation as a civil traffic violation, handled under the procedures in Chapter 5, articles 3 and 4. 02 on top of whatever penalty is assessed. Because it is an equipment offence rather than a moving offence, an officer who sees studs in June has grounds to stop the vehicle and cite it; Arizona has attached no secondary-enforcement limit to § 28-958 of the sort it wrote into the licence-plate statute at § 28-2354(E).

The owner who knowingly lets the vehicle out on studs after May 1 commits the same violation as the driver under § 28-921(A)(1). Violating a local seasonal restriction adopted under § 28-1106 is a separate matter, and is unenforceable unless the required signs were erected and maintained.