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.
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 (onstudded 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
