Record your saddle position before the old bike leaves
A line on the seatpost records seatpost extension. It does not, by itself, record saddle height for a different frame. Before selling or dismantling a comfortable old bike, make a position record you can actually reuse.
Record the saddle model and the exact point used for measurement. Measure relative to a clearly identified bottom-bracket centre, keeping the measurement path and units in your notes. A different saddle shape may put the same reference mark in a different relationship to where you sit.
Record height and horizontal setback with their reference points.
Record saddle angle and rail/clamp position.
Include crank length and the cockpit setup.
Use photos to explain the measurements
Take level side photographs and close-ups of the clamp and visible markings. Use removable tape for a temporary reference rather than damaging the post. Keep the manufacturer’s minimum insertion and rail-clamping limits visible in the record. Do not treat a photograph’s perspective as a precise dimension.
The LightCarbon LCR018-D is an example of a new frame whose actual post and geometry need checking. Copying the old exposed-post length onto it would ignore differences in frame and clamp arrangement.
LightCarbon LCR018-D · Model detailsManufacturer’s example build on the LCR018-D frameset; pictured parts are not a confirmed sale package.LightCarbon; see sourcePhoto unavailable; open the source to view it.
Give the record to the assembler
Ask whether the proposed frame, post and saddle can reproduce the reference within approved limits. If the saddle or crank changes, make that explicit. Check the finished position before permanent setup choices.
If the old position was uncomfortable, record the problem as well and seek an appropriate assessment. A carefully copied bad setup remains a bad setup; the measurements should help the next conversation, not freeze it.
For a crank change, use the shorter-crank guide to separate the new pedal circle from a saddle-height decision. The stack-and-reach guide explains why frame coordinates still need translating into contact points.
