When I worked as a mechanic in Philadelphia in the late 1960s and '70s, the first snowfall brought all repair work in our shop to a halt. We were overwhelmed with customers asking us to swap out regular tires for winter ones.
Without fail, the next summer, drivers who left their winter tires on instead of changing them out would complain about poor handling, especially during rainstorms. (This was especially true with drivers trying to squeeze one more season out of old winter tires before buying a new pair.)
One customer told us driving in a downpour was worse than driving on ice. That's because low tread depth on tires not designed to squeeze water out from beneath significantly increased hydroplaning.
Winter tires are made with distinctly different rubber/chemical compound blends than summer or all-season (actually three season) tires. This composition helps winter tires stay soft and flexible in temperatures below 40 degrees, ensuring better grip on road surfaces.
Expect a 40,000-mile life span for winter tires. Replace them when the tread falls to 4/32-inch.
All-season tires provide a firm grip over wider temperature ranges and road conditions. Their tread patterns quickly channel water from under the tire, reducing the possibility of hydroplaning. On the flip side, properly cared for all-season tires may last up to 80,000 miles. They can be driven safely until the tread reaches 2/23-in.
However, all-season tires become rigid and don't grip the road as well when temps drop below freezing. Loss of grip compromises steering, handling and braking distance.
Before all-season tires became standard in the late 1970s, for years people in Northern states customarily changed from regular to snow (winter) tires. As winter tires improved, many drivers in the snow belt and other cold weather regions of the country still swap them out.
Rubber compounds keep winter tires flexible in snow and ice so they don't freeze. Tread patterns with gripping edges offer drivers increased traction, handling and maneuverability on snow and even ice-covered roads. These qualities provide greater control and performance while increasing fuel economy during the winter.
All-season tires provide a good balance of tread pattern and rubber/chemical mixtures. They offer several benefits in temperatures above 40 degrees - increased driving comfort, longer tread life, efficient braking and fuel economy.
Unfortunately, the same superior characteristics that make winter tires excellent in cold temperatures are their undoing when it's hot.
A lot. Winter tires in warm temperatures are not as responsive when turning or braking, especially when anti-lock brakes or the stability control system engage. A high-speed panic stop on a dry road can quickly ruin the tire's tread or cause uncontrollable skidding, resulting in an accident.
Plenty. An overheated winter tire, even if properly inflated, can cause an unexpected blowout. That's a good enough reason for tire manufacturers to recommend you don't drive year-round on winter tires. And when winter tires degrade in warm temperatures, they wear unevenly, resulting in noise and vibrations.
No. There are no U.S. state laws prohibiting you from driving on winter tires 12 months a year. No state mandates the use of winter tires, either.
Many states do restrict when you can use studded snow tires and tire chains. Check with your Department of Motor Vehicles to determine if your state has any specific regulations regarding how these can or can't be used.