Determining Seat Post Length
 

Hello. I am rebuilding a 1999 Serotta and need to quite a seat post. Frame is 54CM (21"). I am 5-8. As I can so far determine perhaps. 250mm would be the right size. But how does one know? Have been looking at other steel road bikes online but haven't been able to see if there is a general "standard" length that comes with steel bikes. Any helpful info would be great since trying to buy a good used post online.

Grace and peace.

Minimum insertion is about 100mm. add that to the exposed post that you think you need to get the minimum length.

On a level top tube bike, 150mm above the seatpost collar should be fine for all but the longest-legged.

Cutting shorter is simple & many are 350mm so that would be for sure long enough.

From the seat tube to the saddle is a general estimate. 100 mm in the seat tube is safe.

A seat post that is too long is not an issue unless it bottoms out on the bottle bosses, and it can be cut if your goal is minimum weight. On the other hand, a seat post that is too short can damage the frame

Thank you, that was super helpful.

Grace and peace.