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Paxan8's avatar

How do you measure a bicycle seat post?

Asked by Paxan8 (462points) October 10th, 2010

I have just purchased a new seat for my bike and it doesn’t work with my current seat post so I have to buy a new one. Most of the bike posts are between 24 and 27.something mm. I measured the circumference of my current post and it’s 82 mm. Should be measuring diameter? and which part the top or the bottom? I looked online and cannot find the answer so I thought someone from here could answer.

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3 Answers

ipso's avatar


From the bottom. The part that goes into the frame.

27.2 mm is very common diameter, however there are countless frame manufacturers who have different standards.

Be sure to get one as long as the one you have, or a smidgen longer.

BarnacleBill's avatar

If your circumference is 82 mm, then your diameter is 26.11 mm

IchtheosaurusRex's avatar

Seatposts come in sizes that have very fine gradations. The diameter of the post should be marked somewhere on the shaft. It is very important you get exactly the right size for your frame, because even a 0.2mm difference will make the post slip or be too large to insert. You can measure the diameter to an acceptable tolerance with a vernier caliper.

The most common diameters for seatposts are 27.2mm, 26.4mm, and 31.2mm. Don’t count on yours being one of these sizes, however.

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