I just got an 18t white industries freewheel to go with my 48t chain ring. Its perfect for street riding imo. Have an LBS unscrew the freewheel for you. Its really quick and easy. You can also be ghetto and pound away with a flathead and hammer. You dont need a tool to put the new one on. Just hand tighten it and ride away. I also doubt you'll need a new chain.