I am considering buying a set of used Winter tires for a 2013 smart fortwo Pure. The tires are Continental but I am unsure about whether they are the appropriate size. The ad for the tires reads "We have a set in stock 1755515 and 1956015 for the PERFECT staggered fit" but the door panel of the car says 155/60 15 front and 170/55 15 rear. Any advise on buying these or any winter tires would be appreciated. I have tried getting estimates on new from local tire stores and it is over $1000. I will have only paid about $8000 for the car