I would like to buy winter tires which will fit 17 inch wheels. Will this give me enough support during the winter or should I stick with 16s for my cooper s?

 

Ultimately, it is better for snow traction to downsize your winter tires. Narrower so you have a lesser tendency to "float," and taller profile to deal with the winter pot holes. However, it depends on how much snow you expect to drive in, since downsizing also degrades corning performance somewhat.

I live in CT and ski in VT, and I'd have to say, that when it does snow, they clear the roads very quickly so that I feel I drive <5% of my mileage on snowy surfaces. With a 95/5%, clear/snowy road ratio, it was pretty easy to stay with stock (S-Lite) size 204/45-17s snow tires, and just take it a bit easier 5% of the time. Least I know I won't get stuck. I've also done the same with my other car with 225/45-17s.... no problems and on my 5th winter now.

Not many winter tires in that 205/45-17 size, though. I got the non-run flat Pirelli 240 Snowsport and have been happy with them, although it hasn't snowed yet.