Tire Talk – Winter Tires

The single most highly engineered part of your vehicle may surprise you…it’s your tires! No seriously…it is. Considering the season, I’m continuing my “Tire Talk” series with Winter Tires. The most common three questions I get asked all the time about winter tires are “How can I tell a Winter Tire from a regular one?”, “Do I really need them?” and “What’s the difference?”.

 

Winter Tire Symbol

Firstly, a dedicated Winter Tire must have a special marking on the side which is an industry standard indicating that the tire conforms to certain guidelines for winter driving. The sidewall of the tire will have a mountain with a snowflake in the middle like the one shown here. If it’s only the mountain and does not have the snowflake, it’s an All-Terrain or Off-Road tire and not suitable for winter conditions.

To answer the second question, it depends on where you live. If you live in North America, south of the 40th Parallel and at lower altitudes, you probably don’t need winter tires. However, if you live in a place that regularly gets snow or temperatures of below 10C (50F) you should seriously consider getting them as soon as the temps consistently drop to that level. There is a sort of ‘go-no go’ threshold of +7C (44F), which is when winter tires start out performing All-Season tires (also known as ‘no-season’ tires because by design, they are a compromise tire). People expect All-Season tires to perform in temperatures ranging from -30C to +55C (-22F to +130F) which is unrealistic. Don’t get caught up in a false sense of security provided by TV marketing that says All-Season tires can perform perfectly in all conditions. It’s also important to note that winter tires should not be used year round. In warmer temperatures, they become too soft and they will now provide less grip than a dedicated summer tire.

Click for larger image

Hankook Optimo 4S

To make things more confusing for consumers, there is a new tire on the market called an “All-Weather” tire. This, like the All-Season tire, is a compromise tire. Although it bears the Winter Tire Symbol, only the inside half of the tread is winter rated. The outside tread is a summer compound. This is NOT a tire I would consider putting on a vehicle I own anymore than I would consider All-Seasons.

Now to answer the third question; I could simply say that they are designed differently, however how they are designed differently is far from simple. Not only is the tread of the tire very different (I’ll get to that later) but the compound of the rubber is designed differently and is engineered to actually grip ice. They even grip a dry, cold road better than an All-Season tire because they are designed to stay soft at colder temperatures. Lets talk about basic physics for a minute to explain how this works. It basically comes down to heat, friction and pressure and how molecules react to each. When molecules get colder, they slow down and get closer together and become hard. Just think about water turning into ice as the temperature passes below the freezing point of zero Celsius (32F). This is a physical reaction as elements pass from gas to liquid to solid.

Okay, before you get bored with the physics lessons, the same thing happens to rubber. If you heat up rubber too much, it melts (think skid marks on the road when the rubber melts and is left on the ground). If rubber gets too cold, it becomes incredibly hard (think hockey pucks). One of the reasons that hockey pucks are so hard is so that they can slide freely across the ice and so that they don’t deform from the impact of the all-mighty slap-shot. The last thing you want is a tire that becomes so hard that it slides across the ice on the road and can’t conform to the subtle irregularities of the road surface. This is what a winter tire is designed to do and to do that they add more silica to the rubber compound. This keeps the rubber soft so that it can grip not only cold road surfaces but also ice. Believe it or not, ice actually has a lot of grip – when it’s colder than -15C (5F). Ask any hockey player or figure skater and they will tell you they hate skating on ice that is too cold.

Goodyear Ultra Ice WRT

The reason ‘warmer’ ice gets slippery is again a matter of physics – pressure and heat. When molecules are compressed, they heat up, and at a molecular level a very fine layer of water is formed on top of the ice when you walk or drive on it. It’s this fine layer of water that makes ice seem slippery. This is where the tread design of winter tire shines. Winter tires are comprised of lots of tiny little slits in the tread blocks called ‘sipes’ and it’s these little slits (clearly seen in the picture on the right) that wick water up into the tire allowing the tread blocks to grip the solid ice underneath. These sipes also increase the flexibility of the treads so that they can grip the road and ice better.

Winter tires are also broken down into two groups; Winter radial and Snow radial. The main difference is that a ‘snow radial’ has wider spaces between the tread blocks to help cut through deep snow (it resembles an off-road tire). The Goodyear tire shown here is indeed a winter tire but perhaps not ideal for those living in areas with a lot of very deep snow. Please don’t confuse a Mud & Snow tire as a Winter Radial though. Mud and Snow tires have a “M+S” marking on the sidewall. This is basically still an All-Season tire with deep tread to cut into mud and snow but in winter temperatures, the tire still becomes rock hard, unless it also bears the mountain and snowflake symbol.

Important note: Installing only two winter tires is dangerous! Regardless if your car is front wheel drive, rear wheel drive, or all-wheel drive, you should always install FOUR winter tires. Installing only two on the front of the vehicle will greatly increase the chance of fishtailing (over-steer), where the rear end of the car has no traction and tries to ‘pass’ the front. Installing them only on the rear of the car reduces your ability to steer. You are more likely to experience under-steer (when you turn the wheel but the car keeps going straight) and slide right off the road in a corner or on a highway ramp.

Yes this may be a lot to digest but a good tire shop, who sells all brands and types of tires, will be able to assist you in purchasing a winter tire that suits your needs. Depending on where you live, you may also be allowed to install metal studs into your winter tires (the holes for them are already there on some models).

Stopping distances from 50km/hr from MTO Website

The reality is that the worst performing winter tire on the market will out perform the best All-Season tire in winter conditions and provide better stopping performance. Winter tires provide up to 40% more grip in winter conditions than an All-Season tire and that could be difference between losing control of your vehicle and making it home safely.

In the late winter of 2012, I was asked to assist the ILR Winter Car Control School perform some practical testing and comparison between winter tires and all-season tires. In this video you can clearly see how winter tires out performs all-season tires, even against a high-tech BMW all-wheel drive SUV.

So when the temps start falling and the snow hits the fan, you can bet your bumper that I will be driving with winter tires on and so should you.

Click here for more Tire Talk articles and drive safe out there.

EDIT: M+S is actually a ‘wear rating’. We’ve been told is means Mud & Snow but it has nothing to do with a tires ability to handle either mud or snow. It’s just something we’ve become used to seeing on the sidewall of our tires so most manufacturers just leave it there. When you see high performance, low profile tires on a sports car with a tread pattern that wouldn’t even be good in the rain, the M+S stamped on the side is just for marketing.

 

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