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I currently have an older Dahon Mariner with a Telescope seat post. The third wheel that functions as the "third leg" (when the bike is folded) has broken off. To compensate, could I switch out the telescope seat post with a longer seat post. When the seat is dropped for folding, my intention is that the length of this seat post will resume the function of this third leg.

Is this possible?

My model does have a hole in the frame's bottom, allowing a long seat post to pass through (and function as a stand).

Update: Thank you for all the comments below. I am still looking to do this and now have the measurements of the current Telescope seat post. They are 34.2mm and 28.x respectively. The bike does have a small plastic shim between the frame and the bottom telescope seat post pole.

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"Is it possible?". Well, I would say it is possible if it's not impossible. And most probably is a perfectly fine solution with no side-effects. –  heltonbiker Nov 21 '12 at 13:58
    
Do different seat post have different diameters? The telescope seat post on the folder is wider than the seat post on my full size, off the shelf bike. –  Richard Nov 21 '12 at 15:54
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Modern Dahons rest on the bottom of the seatpost, and have no third wheel. Without knowing the details of your model, I doubt anyone will know whether a suitable replacement seatpost exists though. Does your frame seattube allow a seatpost to go right through and out the bottom, like modern Dahons? –  armb Nov 27 '12 at 16:24
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Current Dahon seatposts are 33.9mm diameter. The standard ones are 580mm long but there are longer ones available (e.g. thorusa.com/accessories/seatpost.htm), and suspension posts, and Biologic ones with an integrated pump. But I can't tell you whether your older Dahon used the same size - I've never seen one with a "third wheel". –  armb Feb 5 '13 at 14:19
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Here's a replacement/aftermarket "third wheel". I don't know whether it will fit your older size seatpost though handsonbike.blogspot.sg/2012/07/… –  armb Oct 1 '13 at 10:14

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