Winter / Snow Tire Tech

Studded Tires for Winter Driving

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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 and 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. While it is always good practice to check with local law enforcement officials to confirm restrictions in your area, the state-by-state list of restrictions on studded tire usage is below.

Stud Laws by State
State Legislation
Alabama Studs of reasonable proportions are allowed when required for safety because of snow, rain or other conditions tending to cause a vehicle to skid or slide.
Alaska North of 60° Latitude - Permitted September 16th - April 30th.
South of 60° Latitude - Permitted October 1st - April 14th.
Arizona Studded tires are permitted from October 1st - May 1st.
Arkansas Studded tires are permitted from November 15th - April 15th.
California Studded tires are permitted from November 1st - April 30th.
Colorado Studded tires are permitted.
Connecticut Studded tires are permitted from November 15th - April 30th.
Delaware Studded tires are permitted from October 15th - April 15th.
Florida Studded tires are not permitted.
Georgia Studded tires are not permitted unless required for safety because of snow, ice or other conditions tending to cause a vehicle to skid.
Hawaii Studded tires are not permitted except on either the Mauna Kea access road above Hale Pohaku or on any other road within the Mauna Kea Science Reserve leased to the University of Hawaii.
Idaho Studded tires are permitted from October 1st - April 30th. Fire departments are exempt.
Illinois Studded tires are not permitted. Rural mail carriers and persons with disabilities living in unincorporated areas may use studs from November 15th - April 1st.
Indiana Studded tires are permitted from October 1st - May 1st.
Iowa Studded tires are permitted from November 1st - April 1st.
Kansas Studded tires are permitted from November 1st - April 1st.
Kentucky Studded tires are permitted.
Louisiana Studded tires are not permitted.
Maine Studded tires are permitted from October 2nd - April 30th.
Maryland Studded tires are permitted from November 1st - March 31st for vehicles registered in Allegany County, Carroll County, Frederick County, Garrett County or Washington County only.
Massachusetts Studded tires are permitted from November 2nd - April 30th.
Michigan Studded tires are not permitted.
Minnesota Studded tires are not permitted. Rural mail carriers may use studded tires under certain conditions from November 1st - April 15th.
Mississippi Studded tires are not permitted.
Missouri Studded tires are permitted from November 2nd - March 31st.
Montana Studded tires are permitted from October 1st - May 31st.
Nebraska Studded tires are permitted from November 1st - April 1st.
Nevada Studded tires are permitted from October 1st - April 30th.
New Hampshire Studded tires are permitted.
New Jersey Studded tires are permitted from November 15th - April 1st.
New Mexico Studded tires are not permitted unless required for safety because of snow, ice or other conditions tending to cause a vehicle to skid.
New York Studded tires are permitted from October 16th - April 30th.
North Carolina Studded tires are permitted.
North Dakota Studded tires are permitted from October 15th - April 15th. School buses are exempt.
Ohio Studded tires are permitted from November 1st - April 15th.
Oklahoma Studded tires are permitted from November 1st - April 1st.
Oregon Studded tires are permitted from November 1st - March 31st.
Pennsylvania Studded tires are permitted from November 1st - April 15th.
Rhode Island Studded tires are permitted from November 15th - April 1st.
South Carolina Studded tires are permitted.
South Dakota Studded tires are permitted from October 1st - April 30th. School buses and municipal fire vehicles are exempt.
Tennessee Studded tires are permitted from October 1st - April 15th.
Texas Studded tires are not permitted.
Utah Studded tires are permitted from October 15th - March 31st.
Vermont Studded tires are permitted.
Virginia Studded tires are permitted from October 15th - April 15th.
Washington Studded tires are permitted from November 1st - March 31st.
West Virginia Studded tires are permitted from November 1st - April 15th only on tires operated at 40psi or below.
Wisconsin Studded tires are not permitted. Emergency vehicles, school buses and vehicles used to deliver mail are exempt. Vehicles with out-of-state registrations are exempt only if such automobile is in the course of passing through the state for a period of not more than 30 days.
Wyoming Studded tires are permitted.



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 and 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.

 
#11
#12
#13
#15
#16
#17
 

Only new tires that have never been driven on can be studded. Tires already driven on cannot be studded nor re-studded. This practice risks serious tire damage resulting from incorrect stud lengths and/or unseen debris (sand, cinders, salt or stones) becoming trapped under the stud in the molded hole.

Because studdable 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 (see illustration below). Stud sizes are identified by their Tire Stud Manufacture Index (T.S.M.I.) number or the stud's overall length in millimeters (mm). New studs are color coded to ease identification.

Stud Identification
T.S.M.I. Number Metric Designation Overall Length(mm) Housing Color
#11 8.8 - 10/1 10 Blue
#12 8.8 - 11/1 11 Silver
#13 8.8 - 12/1 12 Gold
#15 8.8 - 13/1 13 Blue
#16 8.8 - 15/1 15 Silver
#17 8.8 - 16/1 16 Gold


Stud Insertion

Typically 80 to 100 studs per tire are inserted into holes molded in the tire's tread design. A special tool spreads the rubber and inserts the stud.

This illustration shows a stud hole molded into the tread when manufactured, as well as studs properly installed, inserted too shallow or too deep.

Stud Insert Diagram

The following pictures show tires studded correctly, as well as those where the studs were purposely inserted too shallow or too deep.

Studs Correctly Inserted


View photo A correctly inserted stud will only have its carbide pin protrude past the tire surface after 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


View photoIf a stud that is too short 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


View photoConversely, if a stud that is too long 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 and 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 tires, once studded tires wear down to approximately 5/32" of remaining tread depth, they will lose effectiveness in deep snow and a new set of tires should be installed if deep snow driving is still anticipated.

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