Sun rims S-Type?

cpk1

Is it just me or the tyres really hard to get off these rims? Im currently running michelin mountain extreme, dual compound tyres. They seem to be really tight initially to get over the edge of the rim when removing the tyre!! puttin the tyre on is difficult but not too bad, is this normal or am i missing a trick, if i get a punture out on the trail i might aswell start walking!!!