Seatpost length

I have a Tarmac SL7 and I just purchased a zero setback seatpost. The frame size is a 54 and the seatpost length is 300mm. This frame normally comes with a 380mm post but specialized was sold out. I’m 5’8” with a 30” inseam so I was wondering if I can make this seatpost work in a 54 frame or will it be too short?

Quick check is to mark the seat post at the height where it enters the frame, while it’s at your proper saddle height. Then remove the post and see how much extra you have in the frame (below your mark) on the current 380mm post. This is the “Current Inserted Length

You should also see a mark showing minimum insertion of that post. Measure it so you know that number, this is the “Minimum Insert Length”.

  • Take “Current Inserted Length” minus “Minimum Insert Length” equals “Extra Inserted Length
  • CIL - MIL = EIL

As long as EIL is longer than 80mm (the amount your new post is shorter), then you should be fine. If your EIL is shorter than 80mm, you may be exceeding the MIL for the new, shorter post.

  • The above assumes that the long and short post have the same MIL, which is likely but not certain. So you should check that shorter post when it arrives to be sure.
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