How do I know what size seatpost I need?
Most good quality posts have the size stamped under the “Minimum Insertion” line. The size corresponds to the outside diameter of the post in tenths of millimeters (e.g. 26.8 mm, 27.2 mm, 32.4mm, etc). If there is no stamp or no post, then it’s time to break out the calipers. To prevent damage to the frame, a very precise measurement is needed. Using a Vernier caliper or micrometer, measure either the inside diameter of the seat tube of the frame or the O.D. of the seatpost in tenths of millimeters. No calipers? Call the manufacturer or take the frame to a professional.
