I have a Raleigh M50 mountain bike. The stock tires are mountain tread but not too aggressive. I am considering getting some smoother street tires for road use. The tires that are on there are 26x2.10. I was told from someone at a local shop that I could use thinner tires for the street but I am confused as to which tire would work. Do I need to use only 26x2.10's or will something thinner work. I don't really understand how something thinner would fit because I am keeping the same rims and would assume that I would need the same size rubber for the rim. Is there a range of sizes that would work properly with this rim size? Thanks