Math. Suspects have a waist width of 86mm, as long as your brakes are wider than 86mm they will not catch on the sidewall. You don't want them too wide, or else they will catch on the snow when carving. Usually you want your brakes to be no more than about 10mm bigger than waist width. Since your brakes are 90mm that gives you a 4mm buffer (actually a bit more, brakes a usually a few mms more than they are listed).