Studded tire report

A studded tire report was commissioned by the state of Washington to learn how well they worked.  We review their findings....




Study Of Studded Tires For Traction And Safety

The state of Washington commissioned a study of Studded Tires to determine how effective they were in improving traction and safety. The Studded Tire Report was published in November 2002.

Summary of the Studded Tire Report

The report is an extensive review of research on the performance and safety of Studded Winter Tires (SWTs). While it recognizes the negative impact of studs in tires on pavement, the report focuses on the performance of late-model vehicles equipped with current generation of SWTs, as well as those equipped with a newer “studless” winter tires such as the “Blizzak” design made by Bridgestone/Firestone.

SWTs have been controversial for years. Some states have banned them, while others restrict their use. (Studded tire Regulations).

Many issues surround the use of studs in tires including:

  • the advantages and disadvantages of improved icy-road traction performance versus the cost of pavement damage.
  • how to define traction performance
  • the conditions under which SWTs are compared with other tires
  • the "safety" of SWTs as measured by traffic incident data
  • driver behavior while using SWTs based on drivers' perception of safety
  • secondary effects, including
    • dust from road wear
    • reduced vehicle control on roadways rutted by stud wear
    • the potential for improved traction characteristics on roadways "roughened" by studded tire use
    • the cost of SWTs in comparison with new studless winter tires
    • the increase in fuel consumption for studded versus studless tires
    • the possible trade-off in the use of traditional snow-clearing methods

REPORT CONCLUSIONS

  1. Studded tires produce their best traction on snow or ice near the freezing mark.

  2. SWTs give better traction than studless tires only under a narrow range of conditions.

  3. The conditions under which SWTs give better traction relatively rare.

  4. Traction improvements can be looked at many ways, including braking, acceleration, cornering, controllability, and hill climbing. While these are all important, the single best indicator of tire performance is braking distance and stopping time.

  5. SWTs reduce the difference in friction factor between optimum-slip and locked-wheel braking in comparison to non-studded tires. This may reduce the risk of drivers misjudging the necessary braking distance and may improve the braking potential for anti-lock brakes.

  6. In one set of stopping distance tests in Alaska, studded, studless, and all-season tires performed nearly equally on snow.

  7. In another set of tests in Alaska, studless Blizzak tires offered the best traction performance, especially for braking on both packed snow and ice in comparison to studded tires.

  8. The use of two SWTs on the front of a vehicle produced stopping traction results on snow and ice that were about halfway between the result of four SWTs and four all-season tires. However, other control problems such as spinning sideways arise.

  9. On bare pavement, studded tires tend to have poorer traction performance than other tires. This is especially true on concrete; for asphalt, there is little difference in stopping distance between studded and non-studded tires.

  10. The traction of SWTs is affected by stud wear. As the studs wear and become shorter traction decreases until the benefit practically disappears when the stud protrusion diminishes to 0.024 in. (0.6 mm). On the other hand the tread wear (on studded tires) shows relatively little effect if stud protrusion is maintained at 0.039 in. to 0.043 in. (1.0 to 1.1 mm).

  11. In Norway a study concluded that the use of SWTs could to reduce the accident rate between 1 and 10 percent .

  12. Driver behavior issues have been raised which affect the evaluation of SWTs. There is disagreement on these points:

    1. drivers with SWTs care more about safety, hence they drive more safely
    2. they drive faster (because of a false sense of security or confidence)
    3. drivers with non-studded tires avoid driving when weather is severe

  13. Pavement ruts caused by increased wear from studded tires can cause the dangerous conditions of trammeling, hydroplaning on accumulated water in the ruts, excessive road spray, and premature damage to pavement markings.

  14. The roughening of ice and pavement from SWTs provides a safety benefit for all vehicles regardless of weather or not they use studs by helping to prevent formation of smooth, glare ice.

  15. The cost of studless tires is significantly higher than SWTs -by approximately 50 percent.

  16. SWTs increase fuel consumption by about 1.2 percent compared with non-studded tires on bare roadways. But the other effects of unevenness, snow, and ice which can increase fuel consumption by as much as 15 percent are far more significant than this.

  17. Pavement dust created by studded tires and noise from studded tires are concerns in high traffic urban areas.


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