Bicycle Mechanics - seat post (railed) height extender ??

Anyone know of an "male-female" extension that basically adds a few inches of height to a standard railed seatpost?

It would have railes at the bottom, and the same railed acceptor-of-rails at the top for a normal seat.

For seatposts that are just a bit too small, and of a strange diameter, or where the max seatpost length has already been found.

Anyone know of an "male-female" extension that basically adds a few inches of height to a standard railed seatpost?

It would have railes at the bottom, and the same railed acceptor-of-rails at the top for a normal seat.

For seatposts that are just a bit too small, and of a strange diameter, or where the max seatpost length has already been found.

I've never seen anything like this offered for sale. I expect it would be very expensive to manufacture and a new seatpost of the correct length and type would be cheaper. Seatposts are available up to 400 mm in length and shims are available to make standard diameter posts fit almost any odd-size seat tube.

Buy a new seatpost of the correct length

Sidetrak did a suspension insert that did exactly what you are looking for - never seen one in the flesh though. According to http://www.sidetrak.com/Catalog/components.html they still sell them.

Buy a new seatpost of the correct length

Op/HillR: this often times isn't possible. For instance, several folding bikes come with strange seat tubes that can't be replaced, and don't accomodate a large enough inseam for certain riders. But they are often within 50mm of being correct. Can you find a >500mm 27.2mm seatpost?

LWabs link shows that this isn't a very expensive thing to fabricate; no more technology than a seat/seatpost.

Any other solutions others have seen out there?

Op/HillR: this often times isn't possible. For instance, several folding bikes come with strange seat tubes that can't be replaced, and don't accomodate a large enough inseam for certain riders.

Bike Fridays are sized to the owner's specs so they shouldn't have this problem unless you buy a used one and get the wrong size by a lot. If the frame is anywhere near big enough, the original manufactirer should be able to supply an adequate length post. If the longest post available isn't long enough the frame is way too small. Further, there are safety considerations with using an excessively long seat post. There aren't any 500 mm 27.2 mm seatposts for a good reason.

If the frame is anywhere near big enough, the original manufactirer should be able to supply an adequate length post. If the longest post available isn't long enough the frame is way too small.
Bollocks!
Have you seen how short the seatposts are on some older bikes (less than 150mm end to end)? Older French bikes in particular have unique seatpost sizes and they are simply not available nowadays. This is not an ideal solution but it is a viable one.

Bike Fridays are sized to the owner's specs so they shouldn't have this problem unless you buy a used one and get the wrong size by a lot. If the frame is anywhere near big enough, the original manufactirer should be able to supply an adequate length post. If the longest post available isn't long enough the frame is way too small. Further, there are safety considerations with using an excessively long seat post. There aren't any 500 mm 27.2 mm seatposts for a good reason.

HR: First, BF is one of many, many mfctrs of folders.

Downtube folders ships with a 500mm 27.2mm seatpost.

One might argue from the standpoint of a Brompton: it ships with a seatpost that isn't long enough for some, so they sell another. The frame doesn't have to be modified for the longer seatpost.

The mfctr of the seat tube will state whether or not there are safety considerations, not the mfctr of the folder. Because the same torque can be generated with a heavy person on a smaller extension vs. a light person (me) with a long extension. Remember from physics, T = r x F.

http://en.wikipedia.org/wiki/

Bollocks!
Have you seen how short the seatposts are on some older bikes (less than 150mm end to end)? Older French bikes in particular have unique seatpost sizes and they are simply not available nowadays. This is not an ideal solution but it is a viable one.

BTW, I just picked up a Starnord randonnee bicycle in France and have needed to upgrade some of its components. It, too, shipped with a very short (6") seatpost. Which makes no sense, because the frame is ~58cm. To get to 790mm from BB center, which I doubt is all that strange for someone that needs a frame of this size, I had to find a new seatpost. It uses a 25.0 mm post, but I managed to get a 25.4 post in there.

Everything is unstandard on this bike. BB threads are spaced a little off, pedal threads are same pitch, but different height, 124mm OLD rear dropout, ...... At least none of the parts were seized. Still can't find info on this line of bikes or a good age estimate (owner said 10 years, but no way that's true).

Bollocks!
Have you seen how short the seatposts are on some older bikes (less than 150mm end to end)? Older French bikes in particular have unique seatpost sizes and they are simply not available nowadays. This is not an ideal solution but it is a viable one.

"Short" seatposts (Campy's used to be 180 mm) were common before the modern trend to buying the smallest possible frame you can ride came along. Racers were told to ride a small frame because it would be lighter and stiffer. The concept spilled over to the casual rider who wanted to look like a racer. To make the reach to the bars proper, manufacturers started to lengthen the top tubes on smaller frames and, of course, seatposts had to be longer.

Now a rider who would have bought a 58 cm frame in the past buys a 54 or 55 but needs a 230 or 250 mm seatpost. Of course "compact" frames with sloping toptubes, both road and MTB, require even longer seatposts and now we have 300 to 400 mm posts in common use.

jsong, your 58 cm Starnord that came with the 150 mm seatpost was intended for a rider about 5'9" (1.75 M) or a bit shorter. If you need a 790 mm (31.1") seat height, you would have bought a 60 or 61 cm frame in those days. Also, 25.0 mm seatposts are available.

jsong, your 58 cm Starnord that came with the 150 mm seatpost was intended for a rider about 5'9" (1.75 M) or a bit shorter. If you need a 790 mm (31.1") seat height, you would have bought a 60 or 61 cm frame in those days. Also, 25.0 mm seatposts are available.

Problem with this is that I'm already stretched to ride on the brakehoods, and it has a small (~100mm) stem. I think I have a fairly normal body type: 6', 34.5" inseam. Just shows what riding style may have been common in the past.

Jasong,

I am really similar in size to you, I ride a 62 - 64 cm bike. sounds like your starnord has a very longish top tube, or you have fairly short arms. Have you seen a professional fitter? BTW, can you now remove the 25.4 seatpost? I certainly hope you greased it.

Also, 25.0 mm seatposts are available.
Certainly but good luck finding a 23.8mm post, as I needed once.

Certainly but good luck finding a 23.8mm post, as I needed once.

That's right and 25.0 is about the smallest used in the past 20 years or so. What needed a 23.8?

The bike was older than 20 years. The French can be a little difficult sometimes...

Decathlon in France sells a 350mm 23.4 post with two shims to fit between ~25 and I think 28ish. €15 for the kit.

OT: Those adjustable shims aren't too secure and weren't available when I was looking, also France isn't quite next door to me. The problem was solved a decade ago by machining another seatpost to fit but it isn't the easiest solution...

The French can be a little difficult sometimes...

One of the more astute comments I've read recently. :)