The first thing you should do is buy a 37 tooth rear sprocket. They add about 24 km/h to the bikes top speed. you can pick one of these up off
http://www.elstars.com.au/parts_acce...ns_sprocke ts for about $32. Make sure it fits though, they have the mesurements of the sprocket on there so u can match it up to the one you have.