32 might fit, 28 will fit. For what it's worth, I ride fixed (don't call it a ****ing fixie around here.) all year. Last year I did it on 700x28 Kenda Kwik Rollers and went down twice on ice. This year I did it on 700x23 Continental Gator Hardshells and haven't gone down yet. Unless you're actually on ice, which is unlikely because Chicago and the suburbs I've been through ( Oak Park, Evanston, Skokie, Lincolnwood, Morton Grove, Park Ridge, Wilmette, Kenilworth, Winnetka, Glencoe, Highland Park, and Northbrook) keep the roads pretty well salted, you don't need studs. A mountain tire will float over the surface somewhat, as will a bigger CX tire. However, when dealing with slush and snow on roads, I find that thin tires with a lot of pressure cut through all of it and you'll be on the road. Just my $0.02.