My '05 A4 has 235/45 r17 tires.

Can one put 15" rims on there? There is a set of winter tires on rims (205/65/15) being sold locally.

I am thinking not....

 

One resource to help in your decision is to use tire size calculators. Do a search on "Miata Tire Calculator". Generally the stock and new tire size need to be close to within 3% according to the posts I have seen on the net.

I don't know about the size's you are quoting but if you go to tirerack.com and do a search on your car, they generally give you options for stock and alternative.

This is the one I have used before after getting various tire quotes for my car (which are stocks 225/45/17 and for winter I went with 205/55/16).

Tire size calculator