Folding Bikes - Telescoping seatpost diameter?

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jeremyb
04-13-08, 04:53 PM
Does anyone know the diameter of the Telescoping seatpost pictured here: http://www.gaerlan.com/dahon/upgrade/post2.gif

I have an offbrand folding bike that I need a longer 28.6 seatpost for.

thanks
jeremy

itsmoot
04-13-08, 05:12 PM
That looks like my Dahon telescoping post which is 34mm. The size is stamped below the mininum insertion mark:

http://www.geocities.com/mootwalker@sbcglobal.net/Dahon_Telescoping_Seatpost.jpg
jeremyb
04-13-08, 05:15 PM
thanks for the quick reply.

Guess i'll look into other ways to get my seat higher. I saw that Butt Buddy in another post, but hopefully there is another option because it looks funny to me.

j

awetmore
04-13-08, 05:44 PM
I have an offbrand folding bike that I need a longer 28.6 seatpost for.


You can make one pretty easily.

Get a piece of 1 1/8" cromoly (4130) steel with a 0.058" ID. This will have an ID of just over 1" (25.4mm), so a 25.4mm seatpost will fit inside. That is a common size for a seatpost.

To hold the seatpost in place you have top options. One is to drill a hole through the seatpost and your extension and then put a split pin in that hole to hold the seatpost in place. Older Swift Folder bikes used this arrangement. The other option is to cut a slit down the extension and get a seatpost clamp which fits over it. This will give you a telescoping seatpost.

You'll need to paint the final setup, but it will work pretty well. You could potentially use stainless steel instead of 4130, but it isn't as strong.

alex
jur
04-13-08, 05:47 PM
Steel tubing usually have a weld seam on the inside...?

You can get hold of 28.6x350mm seat posts pretty easily. What length do you need?
awetmore
04-13-08, 06:46 PM
Seamless steel tubing is easy to get, at least in the US. It is commonly used for building aircraft. Aircraft Spruce, Speedy Metals, and Online Metals all sell the necessary tubing for this job.
jeremyb
04-13-08, 08:15 PM
Thanks for the info, I just ordered 2 feet of 2024 Aluminum tube:

2024 is a high-strength alloy most often used in aerospace applications. It has a yield strength that is roughly 10 percent higher and an ultimate strength of roughly 50 percent higher than 6061.

It has a 26.8 internal diameter, that I will use a silver 26.8 seatpost and 28.6 silver clamp.

The tubing was $25 shipped from onlinemetals.com

I will post later how it comes out.