- Kamran Imtiaz
This is how you can measure the length of the seat tube by standing the bike upright or securing it in a bike stand. a) Measure from the center of the bottom bracket (where the pedals attach to the frame) to the top of the seat tube. This is how long the seat tube should be. b) Find the center of the bottom bracket. c) Measure from the top of the bottom bracket to the top of the seat tube.