Winter tire sizes are based on one of the following points:
Your Vehicle's Original Equipment Tire and Wheel Size
While not offering a dimensional advantage, choosing winter tires and wheels in the Original Equipment size to seasonally replace the vehicle's Summer or All-Season tires will offer more traction in cold temperatures, slush, snow and ice thanks to the winter tire's tread design and compound that remains pliable in below-freezing and sub-zero temperatures.
The Tire and Wheel Size From Your Vehicle's Base Model
This is often an easy way to select an appropriate narrow tire for your car, van or truck. For example, a 2012 Honda Accord EX Sedan would store its original 225/50R17-sized tires in favor of the 2012 Honda Accord SE Sedan's 215/60R16-sized winter tires on 16" wheels. While only a small dimensional difference, this combination will reduce your cost while increasing your vehicle's wintertime traction.
A Minus Size Tire and Wheel
Minus Sizing uses traditional Plus Sizing techniques in reverse. It combines taller profile tires with smaller diameter wheels. For example, the owner of a 2012 Volkswagen Jetta SEL would store the original 225/45HR17-sized tires in favor of a Minus One 205/55R16-size on 16" wheels (where the wheel diameter is 1" smaller and the tire's sidewalls are ½" taller) or Minus Two 195/65R15-size on 15" wheels (where the wheel diameter is 2" smaller and the tire's sidewalls are 1" taller).
I think before making any decision or buying tires for your car...you need to know about winter tires...check out this link from Contiental Tyres which gives you complete information about winter tires and why you should use it... Continental Tyres -Why winter tyres? #ContinentalTyresAfc