Why do you need them?
All season/summer tires are designed to withstand the heat generated from the road. However, they are not necessarily well equipped to handle cold weather. They stiffen in cold weather, which means that the traction they provide diminishes. That coupled with icy, snowy, and/or slushy conditions can mean that you have little to no traction when driving.
Winter tires are designed to handle these challenges. They are made of a different type of rubber that remains flexible in the cold. Further, their tread patterns are designed to provide extra traction. The treads are deeper and have increased slots and sipes. Sipes are small slits in the tire that act like teeth – biting the ice as you drive.
Where do you mount them?
There are several schools of thought on this topic. Tire manufacturers want you to get a full set of snow tires. They say that this is the best option for traction and control. However, this can get expensive. Beyond the cost of 4 tires, there are other cost considerations. If you just want the tires to be installed on your vehicle, then you need to pay a technician to mount and balance them (or do it yourself).
Some people, especially do-it-yourselfers, like to just have an extra set of wheels with the winter tires already attached to save time and make the transition easier. However, if you need to have a shop switch the wheels for you, they will want you to have tire pressure monitoring sensors in your extra wheels to comply with national tire industry guidelines. So, this ends up being the most expensive option, because you have to pay for 4 tires, 4 wheels, and 4 pressure sensors + labor.
A cost-effective approach is to only get two snow tires, but that begins the debate of where to mount them on the car. According to our Service Manager, David Robinson, traction tires should go on the drive axle, so that means if your car is front-wheel-drive, they would go on the front. The wheels where the power comes from are where you need the added traction control.
However, most tire shops will not mount them this way. They maintain that traction tires should go on the back. Their reasoning is that many drivers have a hard time with overcoming understeer in a slide/hydroplaning situation. They are not willing to risk the liability of you getting into an accident, because you cannot drive in adverse conditions.