TIRE TREATISE

Years ago the Rubber Manufacturers Association (RMA) in the U.S. developed a concept called Mud and Snow (variously called M and S, M+S, M/S) tires to denote blockier-type, high traction tires for applications needing higher traction than normal rib type tires. They outlined a geometric layout of grooves, groove dimensions and an overall look or appearance to the tire demonstrating a focus on traction.  The particulars of this layout were supposed to be met before a tire could be called an M+S tire.

When radial tires came to dominate the market, tire manufacturers exploited the higher traction characteristics of radial tire construction and introduced a class of tires called all season tires. These were basically all M+S rated tires as well. All season tires provided increased winter performance versus summer tires, as well as of course the ability to run one set of tires all year round, for some users. The consumer tire market became so dominated by all season tires that virtually all tires sold were all season tires. Only small pockets of demand for winter and summer tires remained.

As time passed the demands on modern radial all season tires began to include lower noise levels, smoother ride, and longer tread life. Designs that excelled in these areas sometimes struggled to provide an adequate level of winter traction. However the tire-buying public looked to products labeled ‘Mud+Snow’ to actually have substantial winter traction, and in some instances the expectation was more than some all season tires could provide. The market also had true winter tires available, but sometimes it was not clear how to identify them because they only had the M+S label, similar to the all seasons.  There were confusion and safety issues.

The Rubber Association of Canada (now the Tire and Rubber Association of Canada (TRAC)) and the RMA concluded that what was required was a performance-based grading scheme that clearly showed a tire had a minimum level of snow traction in order to  be called a winter tire. The Three Peaked Mountain Snowfl ake (3PMSF) designation was developed and is a system that requires that each tire pass a scientifi c test (ASTM F1805) that evaluates its capability as a severe

snow service tire. Tires that pass the test are deemed to be winter-capable tires and have the 3PMSF mark on their sidewalls. They commonly also have M+S on their sidewalls.

Some jurisdictions require 3PMSF tires as a legal requirement for driving during the winter.

In the realm of winter tires, the market has developed further. The 3PMSF designation originally identifi ed a ‘dedicated’ winter tire, essentially built to be run only during the winter months in wintery conditions, and needed removal in non-winter months. This required a user to run two sets of tires, winters and summers (or all seasons instead of summer tires). However, some manufactures now offer ‘all weather tires’. These tires can be run in all four seasons. But they also carry the 3PMSF on their sidewalls covering use during the winter, usually as well as M+S.

In terms of winter weather capability, one could look at the products in the market this way:

Summer tires – not recommended for winter months, very little traction, could actually be damaged in cold weather.

All season tires – some level of winter traction by virtue of the M+S marking, but not to the extent of severe snow service.

All weather tires – by virtue of the attainment of the 3PMSF grade, they can operate in winter conditions.

Dedicated winter tires – the most capable winter tires with the 3PMSF grade. Provide the highest levels of winter traction available and the safest winter driving option.