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check out this weird suspension seatpost

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check out this weird suspension seatpost

Old 01-23-22, 10:37 AM
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adamrice 
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check out this weird suspension seatpost

Pulled this off a tandem I recently purchased. It was in the captain's position (usually tandems have suspension for the stoker), although the seat posts may have been switched at some point. The tandem was built in 1997, and I suspect the seatpost is of similar vintage. It has no external markings--no limit line, no manufacturer name. I suspect it was made by a guy who was a very capable machinist, but not a great engineer, and who had set up shop making specialty bike parts.

The slider has a hexagonal cross section, and the seatpost clamp subassembly just sits on top of that like a cap, retained by a couple of setscrews. The upper and lower seatpost clamps I suspect were scavenged from a commercially produced seatpost (possibly a Nitto). They are clearly castings that are out of keeping with the machining used on every other part of this.

The bottom has a threaded plug that is used to set firmness, and behind that is an elastomer. The whole thing weighs 410 g. The suspension action is basically kaput at this point.

I'm curious if anyone knows anything about this.



Suspension seatpost

Suspension seatpost: top
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Old 01-23-22, 10:50 AM
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Looks to be pretty straight forward. A sliding shaft suspension post with a no set back seat rails clamp. Mid/late 1990s saw a lot of this kind of stuff.

My issue with this post is that on center clamp with no set back. It either places the seat forward of the usual set back posts position or results in the seat being clamped at the very front of the seat rails. Both might be OK or not. For me I like my set back (and in this use of the term I mean the distance between a vertical line extending up from the BB center to past the front tip of the seat and that tip of that seat) to be in a narrow range. In my case using this on center type of post would result in the seat clamped at the rails forward portion and thus creating a lot of leverage for the load on the seat (my butt) to act on the rails. I've seen way too many bent seat rails from this to want this set up. Your experience might be different. Andy
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