I am looking at the 2 tires commonly available and wondering is there any difference? can you mix and match? Why is it I can find the Goodyear's to buy new but not the Michelin's and so on. I recently got my mk23 and want to get it fixed up with a set of tires of similar quality. The ones that it came with are not bad, however I dug some hunks of metal out of one of them that kind of look like shrapnel so maybe they are going to fail on me one has slices in the side walls too. Any discussion on this would be appreciated.