Mud and Snow, (or M+S, or M&S), is a designation applied rather arbitrarily by manufacturers for all-season and winter tires designed to provide improved performance under low temperature conditions, compared to summer tires. The tread compound is usually softer than that used in tires for summer conditions, thus providing better grip on ice and snow, but wears more quickly at higher temperatures. Tires may have well above average numbers of sipes in the tread pattern to grip the ice. There are no traction performance requirements which such a tire has to meet; M&S relates to the percentage of tread void area.
Dedicated winter tires will bear the "Mountain/Snowflake Pictograph" if designated as a winter/snow tire by the American Society for Testing & Materials. Winter tires will typically also carry the designation MS, M&S, or the words MUD AND SNOW (but see All-season tires, below).
Studded, highly siped, winter tire
Some winter tires may be designed to accept the installation of metal studs for additional traction on icy roads. The studs also roughen the ice, thus providing better friction between the ice and the soft rubber in winter tires. Use of studs is regulated in most countries, and even prohibited in some locales due to the increased road wear caused by studs. Typically, studs are never used on heavier vehicles. Studded tires are used in the upper tier classes of ice racing[33] and rallying.
Other winter tires rely on factors other than studding for traction on ice, e.g. highly porous or hydrophilic rubber that adheres to the wet film on the ice surface.
Some jurisdictions may require snow tires or tire chains on vehicles driven in certain areas during extreme weather conditions.
Mud tires are specialty tires with large, chunky tread patterns designed to bite into muddy surfaces. The large, open design also allows mud to clear quickly from between the lugs. Mud terrain tires also tend to be wider than other tires, to spread the weight of the vehicle over a greater area to prevent the vehicle from sinking too deeply into the mud. However in reasonable amounts of mud and snow, tires should be thinner. Being thinner, the tire will have more pressure on the road surface, thus allowing the tires to penetrate the snow layer and grip harder snow or road surface beneath. This does not compensate when the snow is too deep for such penetration, where the vehicle will sink into the snow and 'snowplow' the snow in front. In this case, wider tires are preferred, as they have a larger contact patch and are better able to 'float' on top of the mud or snow.
