Dumb question about hubcaps

I'm not sure what style hubcaps you have, but most likely the metal tabs that hold the cap tight to the rim are bent in. Try using a pair of pliers or channel locks to slightly bend them out, so it will be a tighter fit on the rim. After installing with a rubber hammer, give it a tug with you fingers. It should stay firmly in place, & must be removed with a pry bar or screwdriver. Hope this helps. John.