You will need a fixed rear wheel, with a 12T cog, and a freewhell(acs, tensile, eno etc.) Or A rear Profile/Echo/King whatever, and a 18T front cog(Echo, plaz etc.) Aslong as the ratio is 18:12 or 18:13 depending on your cranks, it will be fine. You can run a rear freewheel, 16T or something and a 22T front fixed cog, but it's abit pointless. Mat