nahuel, to bad you're in Argentina ,I have both sets of extensions I'd like to sell. If you're going to ride on the street I think you will want the 6 inch ,they will help with your 60ft at the track but are still good on the street ,the stock gearing is actually good at the track , if you gear it down it just wants to wheelie,its a fun bike to race , challenging,and relatively quick for what it is ,have fun and keep us posted !