Im going to enter a marathon in a year and well im 17, almost 18, but i dont have the money to be buying a $600-700 multi-speed bike so im going to be buying a fixed gear bicycle in a few weeks and was wondering if that bike would be good to use in a 26.2 bike tour marathon, even if i add the freewheel or a flip-flop hub to it to make it a single-speed bike?