I would say 700x32 is possible with fenders. It's the tire to brake bridge clearance that is key. If 27" x 1.125" (28mm) + fenders was standard fare on these, then 700x32mm is nominally the same outer diameter. These pre-canti or non-canti (depending on year and place in the hierarchy) ST's were tighter in their clearances than the canti-equipped one. I've owned a 1985 ST400 as well as a 1990 ST400. Love these bikes and want an ST800 / 1000 (anthracite color, plus canti brakes) some day.