When we drove one back through the snows of the Austria Alps in November 2010 it was on 245/50 R18 Pirelli Sottozeros, which are high performance winter tyres. Very expensive, but they certainly worked. BMW does winter wheel and tyre packages. If you can get a 17-inch steel wheel with full winter tyre package for the F25, that's what I would go for. See what you mean about the sizes. Michelin does 235/60 R17a and 225/65 R17 Latitudes, but not your exact size. On the last winter tyre test, the Evoques were on 235/60 R18s.