Likewise for the wheelbase, downtube length is the end result of the designer’s choices same as over the size of The top tube, seat tube, and major tube. Earlier racing bicycles mounted their change levers around the down tube. On Newer versions, These are mounted on handlebars with brake levers. https://dirt-bike-engines47934.diowebhost.com/90044318/how-part-bike-can-save-you-time-stress-and-money