Ok "onza trip" broke my derailleur lol. Im currently riding my bike as single speed 22t on the frount and a 7 speed cassette on the back, im trying to keep it in gear 4 but the chain keeps slipping up and down (i know i need a chain tensioner). Im getting a new rim and im thinking of getting a single freewheel what size would i need to have the bike at a gear 4. Thanks Blake