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Obviously any size winter tire will work far better than summer/all seasons in the same size. But the prevailing intelligence, and common sense, indicates that for the best traction in snow, the smaller the footprint, the better the traction in the snow due to increased pressure (the old 100lb female on high heels vs 200lb man in running shoes - why she dents wooden floors, and he doesn't). The larger footprint will have more of a tendency to float. So, if you go to TireRack.com or most other tire sites, they will recommend you drop down an inch in wheel size, decrease the width, and increase the height to compensate.

Here's an article from TireRack to the point:

Size Selection of Winter Tires
Priorities for Sizing Winter Tires Are Different
Does your sports car, coupe, or sedan use wide, low profile tires that are mounted on large diameter wheels? Or does your light truck use large flotation-sized tires? If you're going to drive through lots of snow this year you'll want your winter tires and wheels in sizes that help put the laws of physics on your side.

A wide, low profile or large tire has to "plow" a wide path through snow which causes more resistance. The narrower the tire, the easier you can get through snow. We'll help verify sufficient load capacity and the appropriate diameter for your vehicle when you speak with one of our sales specialists or use Winter Shop by Vehicle.

Winter tire sizes should be based on one of the following:

The Optional Tire and Wheel Size from Your Vehicle's Base Model
This is often the easiest way to select an appropriate narrow tire for your car or truck. For example, a 2003 Lexus IS300 would store its original 215/45R17 tires in favor of optional 205/55R16 tires on 16" wheels.

A Minus Size Tire and Wheel
Minus Sizing is simply traditional Plus Sizing techniques used backwards. For example, a 2003 Volkswagen Jetta GLX VR6 would store its original 205/55R16 (or optional 225/45HR17) tires in favor of Minus One or Minus Two size 195/65R15 tires on 15" wheels.

In both of these examples, not only would snow traction be enhanced, but the cost of a Base Model or Minus Size winter tire & wheel package is usually lower than a package maintaining your vehicle's original size tires and wheels.


But if you already have the wheels, and you're in an area that is not getting non-stop snow and ice, outfitting your current 2nd set with snows is still a far better decision than no snows at all.

Hope this helps.