Snow Tires: Wide Vs Narrow
The winter season is upon us and with it, purchase of winter tires. The common recommendation is to use narrower snow tires than the typical size that a particular vehicle employs, but why? And is this always the best thing to do?
Narrow Tire Strengths
Contact patch of a narrow tire is longer (in the direction of vehicle travel) and narrower laterally. This helps the tire break through a layer of snow, slush or water when driving on highways. The longer contact patch must keep the weight of the vehicle over any given point longer, which pushes the tire down more and squeezes snow or water out better.
Rain tires used on race cars are often narrower than dry tires, for the same reason.
When driving on the street in light snow or slush, narrow tires break through the snow and water down to the pavement underneath. If the tires can engage the pavement, the vehicle gets much more grip compared to engaging snow, slush or water.
Wide Tire Strengths
What happens when a tire cannot break through the snow to the pavement though? This can happen when there is too much snow on the pavement - in heavy snowfall for example, when the snow accumulates on the roads faster than the plows and salt can clear it. It can also happen when there is no pavement underneath the snow, for example when ice racing or driving on unpaved roads or parking lots.
In these situations I believe a wider snow tire would work better than a narrow tire. A wider tire will float over the packed snow where a narrower tire would tend to sink in. And I believe a wider tire would generate more grip on ice for the same reason that a wider tire generates more lateral grip and drag when used on pavement in road racing.
A wider tire also has a higher chance of not completely falling into a rut, and thus biting into the surface adjacent to the rut, or biting into pavement around an icy spot on the road.
Grip When It Matters Most
Chances are a typical tire would see slush and rain quite a bit more than snow and ice, since roads are generally treated with anti-icing chemicals and plowed in winter. Hence most of the winter driving would favor a narrow tire. However, clear weather happens even more often than slush or snow, yet we buy snow tires - the reason is we need something to get us through the worst conditions we will encounter safely. And arguably ice and packed snow are the most problematic conditions encountered in winter driving, and these conditions in my opinion favor the wide tires. After all an all-season tire is designed to work well in rain and will probably do ok in slush.