Folding Bikes - How are seatposts measured?

I need to put about 40 mm more in length on my seatpost for the R20, and the longest seatpost I can find online is 400mm. If that's a measurement of how much exposed seatpost you can have, then it'll be plenty, but I'm not sure what the length measures on seatposts actually refer to. Does anyone here?

Usually from the very bottom to the saddle rails. 400mm is very plenty, I used 350mm and it was very plenty. Currently I am using a 400mm Thudbuster and it is 'quite far' above the minimum mark.

Are you 6'3 though?

Heh heh, 5'10

If you have some spare cash (who has?) you could get a 450mm Thudbuster with a shim to 28.6mm.

Cut up an old frame they are 28.6mm external diameter on the seat tube. Slot that in the frame. Use the seat pin from the cut up frame. Ive done that on my Raleigh Grifter.

Are you 6'3 though?


Lucky little me. Usually bicycle equipment size medium is already too big for me.

at 5'5" I have to agree. Makes for lighter bikes too woo!

Cut up an old frame they are 28.6mm external diameter on the seat tube. Slot that in the frame. Use the seat pin from the cut up frame. Ive done that on my Raleigh Grifter.

At a pinch I might try this.

You don't need to cut up an old frame. For a seatpost that long I'd buy some 1 1/8" OD steel tubing with a 1" ID. Aircraft Spruce (http://www.aircraftspruce.com) is a good source of this.

You can then pin a 1" seatpost in the top of that. This makes a very long 28.6mm (1 1/8") seatpost. You can use stainless steel or have the tubing nickle plated.

This is how the seatposts were originally made for the steel NY Swift Folders.

This will give you a much stronger seatpost than cutting out an old frame tube. The frame tube will likely be .6mm for most of it's length, butted to .9mm at the base (where you don't need the extra strength). The tube that I suggest will be 1.6mm wall thickness.

"You can then pin a 1" seatpost in the top of that."


>>how would you do this?