Winter Tires

by Drew Wikstrom (bio)

Now that the Holidays are over and everybody can think about their cars again the subject of winter tires seems to be coming up more often than not. Here on the east coast the winter has been somewhat mild so far and many folks are thinking about doing without winter tires this season. In that regard I have been fielding a lot of questions regarding exactly what tires to use during this particular winter season. These questions fall into three basic categories. 1) “Should I stay with my summer performance tires?” 2)“Would an all-season tire suffice?” and 3)“What kind of winter tire should I get?” Let us explore these questions in some detail.

“Should I stay with my summer performance tires?”

The short answer is no. Unless you live in a perpetually summery climate such as Florida or southern California where the ambient temperature never drops below 50 degrees F and it never ever snows then summer tires are not a good choice for the winter season.

Summer tires were designed for warmer temperatures and high stress use. Because of this they have very large stable tread blocks that are not good in inclement weather. In addition the rubber compound does not maintain elasticity in cold weather. What this means is that the grip level of the tire degrades drastically in cold temperatures even on dry pavement. In the cold a summer tire becomes unpredictable and feels “slippery” when cornering no matter what the weather. This problem is compounded in wet or snowy conditions.

“Would an all-season tire suffice?”

The answer to this question is dependent upon several factors. One of which is the driving habits of the user. All season tires tend to be compromised tires. They work reasonably well in a variety of conditions but they do not excel in any one condition.

With regard to winter travel the important compromises are the ones that weaken the winter capabilities of the tires. In an effort to maintain some warm weather performance an all-season tire will have a rubber compound that may not work as well in the cold as true winter tire. This all-season rubber compound may also be further compromised by a need to provide a certain amount of tread life thereby eschewing traction in all conditions in favor of longevity. An all-season tire may have a tread design that trades inclement weather performance for dry road performance by having larger more stable tread blocks than a winter tire.

Anyone who is considering all-season tires for year round or winter use needs to carefully examine their driving habits. If giving up performance to gain more tread life and avoid the hassle of changing over to winter tires is acceptable; then it may well be worth it to utilize all-season tires. Driver’s who are very conscious of the performance capabilities of their vehicle or who want the absolute best traction they can get as a safety margin should not use all-season tires for winter travel unless the climate dictates otherwise.

In some climates all-season tires may be preferable to winter tires because of the temperature range they were designed to work in. In warmer climates where it may only snow once or twice a year a winter tire would wear out very quickly where an all-season tire would work very well by providing the appropriate levels of performance and longevity.

“What kind of winter tire should I get?”

This is the most difficult question to answer because recommendations can vary greatly depending on multiple variables. What is the climate? What are the driving habits of the user? What type of vehicle? Where are the drive wheels? etc. The list of variables can be excessive. Fortunately winter tires can be divided into 3 main categories. High performance winter tires, severe winter tires, and ice tires.

High Performance Winter Tires

High performance (HP) winter tires are the winter equivalent to high performance summer tires. They are designed to have as few dry road handling compromises as possible. The rubber compound is designed with cold temperatures and high-speed travel as a primary focus. HP winter tires are usually “H” (130mph) or “V” (149mph) speed rated although some are “Q” (99mph) or “T” (118mph) speed rated.

The tread design is usually similar to a modern high performance summer tire; it will have fairly large and stable main tread blocks. What differentiates an HP winter tread from a summer tread is that these blocks are spaced farther apart creating a larger “void” area to enhance the evacuation of water and slush from under the contact patch. The main tread blocks will also be inundated with very small cuts known as sipes.

Tread sipes create little biting edges that aid snow traction. They also allow displacement of the boundary layer of water that is created as the tire contacts an ice or snow surface. This is important because this boundary layer of water is a large part of what makes winter travel slippery. This boundary layer of water is the same as that produced by a ski or snowboard as it slides across a snow surface, or an ice skate as it glides across a surface of ice.

HP winter tire manufacturers use a variety of methods in order to maintain tread block stability for good wet and dry road handling. These methods may be, sipes designed in interlocking patterns, tires with reduced tread depth, or stiffer more durable rubber compounds, or rubber compounds enhanced with stiffening agents such as nylon or glass fiber.

Durability is an important part of an HP winter tire because they are meant to withstand sustained speeds and increased mileages on dry road vs. a more conventional winter tire or an ice tire.

HP winter tires are generally used in urban or suburban areas where road maintenance is at its highest and also in climates that are not excessively cold even though they may be snowy. Other HP winter tire users are those that drive mainly on highways and for long distances during the winter months.

Severe Winter Tires

Severe winter tires are generally studless and provide excellent grip in many different snow and slush conditions. The same basic design requirements of the HP winter tires carry over to the severe winter tires with increased performance in inclement weather and sacrificed performance in the dry.

When compared to HP winter tires a severe winter tire will use a softer rubber compound and have more tread sipes. The rubber compound may use very advanced technology such as micro cellular structures or other advanced rubber compounding techniques. More emphasis is also placed on what is known as a “self cleaning tread design”. A self-cleaning tread design traps snow when the tire rolls over it and then releases the snow so it can trap more on the next revolution. In this case snow on snow provides traction when the snow is trapped between the tread blocks. The snow must then be released so that it can get trapped again. If the tread blocks do not release the snow the traction goes away.

The disadvantages to a severe winter tire depend on the tire. The category is very broad and each tire manufacturer addresses large variety of conditions. Some tires specialize very heavily while others are more well rounded.

The main disadvantages to severe winter tires are decreased longevity and decreased dry road performance when compared to HP winter tires.

Severe winter tire users are usually in more rural areas where roads may be snow covered for most of the winter due to lack of road maintenance or excessive snowfall. These users typically do not drive excess mileages on dry road or do a lot of high-speed travel.

Ice Tires

Ice tires are the most specialized winter tires. They are meant to perform well only on ice. The category was created largely due to conditions encountered on the northern island of Japan where the traffic is very slow and winter road conditions are often glare ice. For the North American market these tires are largely unusable. While they provide very good traction on snow and ice they handle very poorly at even moderate speeds and provide very little feedback to the driver. In addition they wear out so fast that in many cases the useful life of the tire spans only one winter season.

The technology in these tires is the same as any of the others. Sometimes the tread design is biased toward ice, in which case it does not work well in snow or slush. In some ice tires the rubber compound is simply changed and an existing tread design is used creating a tire that looks identical to another winter tire but is useful only for driving on ice due to its highly specialized rubber compound.

Ice tires are for drivers that experience icy conditions and slow speeds.

Last Thoughts

All the major tire manufacturers make winter tires for nearly every category. Bridgestone, Michelin, Pirelli, Yokohama, Continental, and Dunlop all have winter tires in at least two categories. Besides the major tire manufacturers Finland’s Nokian is widely regarded as the foremost manufacturer in the area of winter tire technology. Which tires are best for you depends on your climate, the prevalent road conditions in your area and your driving.

When choosing winter tires only choose those that meet the tire industry’s “severe snow service” standard. These can be identified by an icon molded into the tire sidewall that looks like a snowflake within a mountain. Only tires that meet or exceed the industry snow traction test display this symbol. Do not be misled by the old “M+S” (mud and snow rating) as it corresponds only to the “void” area of the tread design and is usually found on all-season tires as well as winter tires.

When choosing tires consider the temperatures they were designed to operate in. Also consider personal driving habits, geographic location and road maintenance. These considerations should provide enough information to determine what tires are the correct ones. The specific attributes of various tires can be found online at any of the manufacturers websites like www.nokiantires.com, at your local tire store, or a national retailer such as The Tire Rack

About the Author:  Andrew (Drew) Wikstrom, is a lifelong automotive enthusiast who finally turned his enthusiasm into a career at Fairfield County Motorsport in Fairfield, CT. USA.  At the age of two when asked what he wanted to be when he grew up he said to his mother “I want to be a truck”.  While he has been unable to reach the lofty goal of becoming a “truck” he has found a good outlet for his knowledge and experience through the careful automotive advice he gives to his customers.

Drew is an active member of the Porsche Club of America and the New England Subaru Impreza Club.  He competes and instructs avidly in local Autocrosses and participates in club sponsored Driver’s Education events as much as possible.

Endurance sports car road racing is Drew’s first love due to its varying challenges of technology, speed, car control skills, and strategy.  He can often be found spectating at amateur and professional racing events on the east coast of North America.