Those are pretty standard ratios from back in the olden days, 42 and 52 up front with a 12 or 13 being smallest at the back and just 1 tooth difference per sprocket.
@Getafix531 started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
Those are pretty standard ratios from back in the olden days, 42 and 52 up front with a 12 or 13 being smallest at the back and just 1 tooth difference per sprocket.