It's Time to Retire your All-Seasons

Consumers in the Winter Tire Belt have it rough. Everyone knows it is safer to drive with season-appropriate tires, but no one wants to pay for an expensive 3rd party storage facility--or worse: store those heavy, dirty tires in a garage and transport them back and forth from a tire store every six months. The demand for all-season tires stems from three major problems facing every American who owns a set of winter tires and a set of summer tires: 1) inconvenient tire changes; 2) high storage costs; 3) space restrictions.

These barriers force many consumers to ignore the risks posed by improper tire usage. Without the option of driving on season-appropriate tires, people either drive year-round on their summer performance tires or resort to all-seasons. The first group is very recognizable; they are in a ditch on the side of the road when winter comes around. The latter group is better prepared for ice and snow; unfortunately, all-seasons still pose major safety risks in colder climates. To put it simply, they are an insufficient compromise that wear out quickly in the summer and provide less traction in the winter.

Here is a quick breakdown of the key differences between summer tires, all-season tires, and winter tires: 

1. The rubber in all-season tires hardens in cold temperatures, which reduces grip and traction. Winter tires have special rubber composition that stays soft and maintains traction in the winter, but wears out quickly in the summer. 

2. Summer performance tires have a shallow tread depth, which is more efficient on dry ground, but allows for snow buildup while driving. Snow tires have special grooves and deeper tread that not only increases traction on snow and ice, but also prevents hydroplaning by redirecting moisture away from the tire. 

3. Snow tires have biting edges, which are zig-zag grooves in the tread that have much better grip on cold pavement. All-season tires land somewhere in the middle of winter tires and summer performance tires, which means they still wear out faster in the summer and are a poor solution for real winter driving.

Experts agree that season-appropriate tires are essential for consumers who drive on ice and snow, or where temperatures consistently drop below 45 degrees in winter months. Now, let's dive deeper into the five categories used to evaluate the performance of seasonal tires: compound, tread depth, sipes, grooves, and studs.

Compound

Tire manufacturers use different materials to form unique rubber compositions based on each tire's purpose. Drag racing tires have a very different rubber composition than consumer street tires, and winter tires have a very different rubber composition than summer tires. This amalgam of ingredients is known as the tire's compound.

As you might guess, the compound in summer performance tires is designed for warm temperatures and dry roads. The tires maintain maximum contact with the road and feature a flexible holding grip for precise handling. These tires are stable and durable with high lateral stiffness. All-season compounds mimic the flexible performance of summer tires, but are also designed to withstand moderately cold climates. When temperatures drop below 45 degrees, the compound on all-seasons starts to stiffen and lose its holding grip. Winter tires, on the other hand, remain flexible in cold temperatures. The rubber conforms to minute imperfections in the ice and snow, allowing for increased handling in dangerous conditions. This feature is a tradeoff because winter compounds wear out quickly during contact with hot asphalt.

Tread Depth

Every crack, knob, and design on the bottom of your tire has a purpose. Tire treads allow drivers to grip the road, stop and accelerate smoothly, and turn efficiently. Tread depth is the measurement from the top rubber layer to the tire's grooves. Tread deteriorates and grows shallower over the life of every tire. Every driver should be aware of his or her tread depth for their own safety, as well as legal reasons.

Summer tires have a tread depth of 1/8th to 1/16th of an inch. All-seasons have a tread depth of 1/4th to 1/8th of an inch. Winter tires have a tread depth of 3/8th to 3/16th of an inch. The second number in each of these ranges is the recommended depth to replace the tire. The range of depth considered safe for each category of tire varies quite a bit.

Sipes

Sipes are tiny slits in the rubber surface to increase tread-surface area. Sipes were originally used to increase traction on the rubber soles of work boots, and were later applied to tires. Some tire designs have thousands of sipes to increase handling and decrease stopping distance in tough conditions.

Summer tires have limited sipes because they are best utilized on snow and ice. All-seasons have hairline channels that create edges and increase traction on wet roads. Winter tires have highly dense channeled patterns featuring small zig-zag shapes. These patterns provide thousands of additional biting edges to handle the most slippery conditions.

Grooves

Most tires designs have both longitudinal and lateral grooves along the length of the tire. Other features include ribs, block, tie bars, and dimples, all of which assist the base groove design. Some tires have 4-6 parallel grooves along the tire, while others have diagonal grooves from both shoulders that meet in the middle.

Summer tire grooves are designed to maximize stability, evacuate water, and manage tire heat when roads are overly hot. All-seasons feature slightly deeper grooves designed to evacuate water and handle moderate conditions. Winter tires have the deepest grooves with sharp, irregular edges for increased traction on snow and ice. They sacrifice on stability in summer conditions when compared to the other two categories.

Studs

Tire studs are tiny metal protrusions that can be installed in the tread of studdable winter tires. Studs should not be used on dry roads as they can limit rubber contact in regular conditions. They are proven to increase grip on hard-packed snow and ice.

Summer and all-season tires never feature studs. Some winter tires allow studs to be installed when the driver is planning on driving on heavily snow-packed roads.

Societal Impact

The Traffic Injury Research Foundation has taken a very clear stance on winter tires. A TIRF report titled Winter Tires: a Review of Research on Effectiveness and Use collected data from hundreds of studies from all over the world and came to 3 important conclusions:

1. "Winter tires are superior to summer tires and all-season tires in terms of traction, braking performance and cornering in all winter conditions."

2. "Winter tires outperform other types of tires during all winter conditions, including dry surfaces, once temperatures drop below +7 degrees Celsius."

3. "In winter driving conditions such safety features like ABS, Electronic Stability Control (ESC), AWD or four-wheel drive are compromised without the use of winter tires" (Brown).

The study also found that cars with winter tires took "18 meters to stop whereas the car with all-season tires took 27.1 metres" (Brown). This 33.6% reduction in stopping distance is enough to save countless lives.

The Winter Tire Belt of the United States has taken notice of the risks posed by driving without season appropriate tires. More and more areas are mandating the use of winter tires during winter months. For example, Colorado Governor Jared Polis passed a law in the spring of 2019 putting new tire traction requirements in effect on a 127-mile stretch of I-70 from September 1st through May 31st. The law increased mandatory tire treads during winter months from 1/8 of an inch to 3/16 of an inch. To be an approved tire under the traction law, all tires need to have a snowflake mark (designating a snow tire) or a mud and snow (M+S) mark. The major change is that the requirements for adequate tires and traction control devices now apply to passenger vehicles, unlike before. While the bill specifies the I-70 mountain corridor between Genesee and Dotsero, this does not limit the applicability of the law to this corridor. CDOT traction and chain laws apply to all state highways.

The question remains: will this legislation actually make Colorado roads safer? Fortunately, the data says yes.

Quebec, Canada took steps to ensure safer driving by mandating winter tires in December, 2008. A 2011 Transports Quebec study reported a 36% reduction in people killed or seriously injured after the change in legislation. During the winters of 2003 through 2008, an average of 822 people were seriously injured or killed. During the winters of 2009 and 2010, the average dropped to 523 injuries/deaths. The city of Montreal reported a 44% decrease in injuries and deaths during this period (Transports).

Sweden passed a similar piece of legislation in Sweden in 1999. A study by the Swedish National Road and Transport Research Institute reported an "11-14% reduction in collisions, and an 8% reduction for injury collisions" (Brown 15). The law "resulted in 7-9 fewer fatalities and 49-63 fewer serious injuries," when comparing the winter directly before the legislation to the winter directly after (Oberg).

US territories are unlikely to pass widespread legislation mandating the use of winter tires until the problems mentioned at the beginning of this article are alleviated. Without a major shift in the tire market, no one can realistically solve the challenges associated with inconvenient tire changes, high storage costs, and space restrictions.

Canada has a robust seasonal tire storage industry that gives consumers access to affordable, convenient tire storage. Until recently, the United States lacked the resources to provide a comparable seasonal tire storage infrastructure.

InvenTire is the tool the US automotive industry was missing.

InvenTire is the end-to-end seasonal tire storage SaaS platform for dealerships, tire stores, and service facilities. Our business model is focused on boosting customer retention for automotive businesses while giving consumers convenient, affordable access to quality tire storage. We are on a mission to educate the public about the risks associated with inappropriate seasonal tire usage, as well as provide win-win solutions for automotive business owners and their customers.

Learn about InvenTire's service offerings at goinventire.com and join the road safety revolution today.

Sign up here to stay up to date with all of our posts!

Sources

Brown, Steve W.; Ward, Vanlaar G.M.; and Robyn D. Robertson. 2012. Winter Tires: A Review of Research on Effectiveness and Use. Traffic Injury Research Foundation.

Oberg, G.; Velin, H.; and Wiklund, M. 2002. The effect of the Winter Tyre Law on the use of tyres and on accidents. VTI Rapport 479. Linkoping, Sweden: Swedish National Road and Transport Research Institute (VTI).

Transports Quebec. 2011. Implementation of a measure making winter tires mandatory for certain road vehicles. Quebec, QC.: Transports Quebec.