It's not a stupid question -- you don't want mud or freezing slush to jam your wheels and cause a crash.
The first set of studded tires I tried on my bike (Kenda Klondike 2.1") were indeed too big to run safely with fenders, so I took the fenders off for that winter. I downsized (and upgraded) to Suomi Mount & Ground 26"x1.9", and I have clearance again.
