Youth size BMX bikes suit riders 130cm to 170cm tall: In this category you'll find 20 inch wheeled BMX bikes with top tube lengths from 18.5" - 20.75". The top tube length is the determining factor in getting the right size here. If you're the shorter end, you'll be best off with a 18.5" top tube, if you're 170cm, you will want to get a bigger number top tube.
