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Minimum seat post length

Posted: Tue Jul 25, 2017 8:18 pm
by Monkeychunki
Hi, I presume this has been asked before however I can't find any posts.

I have cut back my 3t seat post to the minimum length however I haven't thought about the fact that the seat tube height above top tube differs per bike... is there a standard measurement that should be followed from a frame perspective e.g. 3cm seat post depth from the top of the top tube?

Re: Minimum seat post length

Posted: Tue Jul 25, 2017 8:27 pm
by djwalker
Every seatpost has a minimum insertion length that is marked on the post. Measure the distance from this line to the bottom of the post. This is the amount of post that needs to be inside the seattube. Once you set your seat height on a particular bike you can cut the post off below the seat tube clamp so that the length of post inside the seattube will be what you measured above. Since the amount of seatpost sticking out of the seattube is usually different on every bike so also will the total seatpost length be different for every bike. So, the post won't be swappable between bikes. And, you also won't be able to raise the seat in the future. For example if you get a different seat. It would be better to leave a few centimeters longer than the minimum for this reason. Note that some seatposts, like my mcfk one, do not allow cutting the seatpost at all.

Re: Minimum seat post length

Posted: Tue Jul 25, 2017 8:27 pm
by Weenie

Re: Minimum seat post length

Posted: Tue Jul 25, 2017 9:28 pm
by Monkeychunki
Ok cool thanks for this it makes sense. I thought that the frame would also have a minimum insertion measurement because I assumed that the seat tube height above the top tube may differ per manufacturer and model. I guess this isn't the case then.

Re: Minimum seat post length

Posted: Wed Jul 26, 2017 2:48 am
by RyanH
That's actually a fair point and I think the rule of thumb is that it should at least pass below where the seat stays meet the seat tube.

Re: Minimum seat post length

Posted: Wed Jul 26, 2017 2:52 am
by Wingnut
I usually go about 1 inch below the top tube to be safe...