corossion, thats whats up. you can carry on with the big hammer, rotating the wheel with each hit, but preferably using a block of wood to prevent damage. if this wont work, apply penetrating oil. if you can get the centre cap off as well that helps as its stuck on the spigot. once it comes off, and it will, thoroughly clean the wheel and hub, until the wheel goes on easily. then apply a coating of copper grease to the contact points. if you do all 4 now, it saves this bother when on the hard shoulder with a flat.