I know you'll think I'm a little nuts, but I have a perfectly good mountain bike which I only ride on streets and paved trails. This is in flat Florida. I would change out the tires to 26 X 1 1/2 and replace the cassette/free wheel with one meant for a street bike and the front sprocket also. Add a new chain if necessary. Any thoughts about the deraillieures? I have the tools necessary. I'd appreciate some thoughts.