My new mountain bike comes with tyre size 26 x 2.0. They are off-road tyres but as I want to use the bike in a race in August, I'd like to put slick tyres on it. Can I choose any slick tyre that is 26" in diameter or do I need to look at something else as well? Continental, for example, have the Ultra Gatorskin that is 26 x 1.2 or the Travel Contact that is 26 x 1.75. The Specialized Armadillo is 26 X 1.95. I just don't understand tyre size and I can't find a website to help. The ones above all seem like good tyres for the road and bike track that I'll be using them for, but will they fit? Would I be better buying new wheels with slick tyres?