I am a college student at the University of Toledo (Go Rockets!!) and recently I have started biking for a couple of reasons. first is so that I can lose some weight cause im 5'8'' and i am at 172 right now and i would like to get down to 160 the other reason i started cause i like getting out on the bike trails and local metroparks to ride. currently I have an older mountain bike that I am riding. My first question is should I stick with the off road style tires or should I move to a smooth tread tire. All of the places I ride are paved. A friend of mine is willing to give me a set of tires like this [ame="http://www.amazon.com/Pyramid-Tire-Black-Kwest-60Psi/dp/B000XNXUMY/ref=sr_1_32?ie=UTF8&s=sporting-goods&qid=1243730476&sr=1-32"]Amazon.com: Pyramid Tire 26 x 1.95 Black/Black Kwest K193 60Psi: Sports & Outdoors[/ame] . would it be worth putting some money into this bike so that it lasts or should I just save up and buy a road bike of some kind. I am open to all suggestions. Also I ride about 12-15 miles a day on the weekdays and then about 20 on saturdays. Thanks for the help.