depends on the bike. the sidepanels on my old cb750 cover the oil tank. it sounds like your side panels have some sort of surface contamination in them that's preventing the paint from sticking. sanding it won't necessarily work. you'd have to wipe them down with some sort of prep-sol or other solvent to get rid of the surface contamination. moto parts get all kinds of crap on them and most of them are abs plastic, so i think they tend to absorb things.