Introduced in the United States in the 1960s, metal studs that could be inserted into tires were developed to enhance traction on the slipperiest road condition...ice. The studs were designed to use the vehicle's weight & centrifugal forces to provide more ice traction as they repeatedly chipped into the driving surface. However, when the road wasn't covered with snow or ice, tire studs noisily chipped into the road itself. So studded tires are good for ice traction, but not good for roads. The use of studded tires is said to cost taxpayers millions of dollars in road wear every year. Additionally as studded tires chip into the concrete, they eventually cut ruts in the road that will fill with water to create a hydroplaning hazard when it rains. This has prompted states to prohibit studded winter tires completely or restrict them to seasonal use. Check with local law enforcement officials to confirm restrictions in your area.

In addition to road damage, air pollution contributed to studded tires being prohibited in Japan where concrete dust was measured in the air along busy highways during winter. This immediately led Japanese tire manufacturers to develop "studless" winter tires that use special tread rubber compounds in place of studs to provide enhanced ice traction. However, none of these "studless" tires can totally equal a studded tire's traction on all types of ice.

Tire studs consist of two primary parts. The tungsten carbide pin is the element that protrudes beyond the tire tread & contacts the pavement surface. The outside part of the stud is a cylindrical metal jacket or body that is held in the tire tread rubber by a flange at the base.

Because studdable winter tires are manufactured with different tread depths, studs are manufactured in different lengths that must be matched to the depth of the holes molded in the tire. The stud number also reflects the depth of the molded hole (see photo below). New studs are color coded to ease identification.
 

#12 #13 #15 #16 #17 Note: Shown at twice actual size. Stud Identification Stud Number Hole Depth Housing Color #12 12/32" Silver #13 13/32" Gold #15 15/32" Blue #16 16/32" Silver #17 17/32" Gold

Correctly Inserted Studs

Typically 80 to 100 studs per tire are inserted into holes molded in the tire's tread design. A special tool spreads the rubber & inserts the stud. Once the stud is correctly inserted flush with the tire surface & the tool is removed, the tread rubber compresses around the stud's flat head (inserted into the bottom of the hole) to hold the stud in place.

Studs Inserted Too Deep

If too short a stud is inserted, or the appropriate length studs are inserted too far into the tire, they will not reach the tread surface or operate effectively until the tire wears.

Studs Inserted Too Shallow

Conversely, if too long a stud is inserted, or the appropriate length studs are not inserted into the tire as far as they are intended to go, they will protrude from the tire, allowing them to wiggle, possibly enlarging the molded hole & be ejected.

As studded tires are driven through winter, the studs are designed to wear at a rate similar to the tread rubber with the tungsten carbide pins wearing a little slower than the metal housings around them. This retains the stud's effectiveness to continue to chip into the ice as the tire wears. However, as with all winter tires, once studded winter tires wear down to approximately 5/32" to 6/32" of remaining tread depth, they will lose effectiveness in deep snow & a new set of winter tires should be installed if deep snow driving is still anticipated. Breaking-In New Studded Winter Tires Special consideration is required when breaking-in new studded winter tires. In order to facilitate installation of tire studs, the tread is often lubricated (a 2% soapy water solution is desired) to allow the special tool to spread the rubber & insert the stud into the bottom of the molded hole. Once the stud is in place, the tool is removed & the tread rubber compresses around the stud's flat head & cylindrical housing to hold it in place. Because it takes some time for the lubricant to evaporate & the tread rubber to compress around the stud, studded tires require a special break-in period. Relatively slow driving (less than 31 mph/50 km/h) without hard acceleration or braking is recommended for the first 62 miles (100 kilometers). This will allow the lubricant to evaporate & the tread rubber to conform to the shape of the stud. Studded winter tires are not recommend for high speed driving because high speeds, as well as excessive tire spinning, can cause studs to be ejected.

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