I have a spec hardrock mtb that I just swapped Specialized nimbus tires on it. Made a big difference. Made the bike 2-3 mph faster than the knobbies. You will have to change tube. The tires I put on are 26x 1.5 the stock tire was 26x2, the stock tube was too big. Just buy tubes the same size as the new tires. Makes the bike look totally different also w road tires.