I would probably say a 205 would be thin enough. I mean there is a point when you are driving where, you do not want it too thin because that just means that your sidewall will just flex all the time and your car will have some serious wabble. For the winter I run a 15inch wheel. with a 205/60R15. I was told that the 195s just did not have enough meat on them for when there is just normal road.

Oh yeah, I do recommend the Nokian Hakkapalietta's. They are a really quiet tire. It is rated as an M+S tire but it does have the government branded mountain with snowflake on it.

 

You can run a 205/45R17. I believe that is the stock size used on Volvos. Also, I know that you can also find 205/50R17s.

 

I don't think you should run anything smaller than a 205 on a 17X7 rim. You might be risking rim dammage. I have snow tires on my stock RS rims which are 16x7's and running 205/55 Dunlop M2 Wintersports. They are great dry tires for being winter tires.