Seat post failure confusion

Some gentle bumps resulted in a seat departing the horizontal, rapidly
rearward. On inspection, I found the suspension post had fractured
(almost all the way from front to back) at the top of the fixed section
where there is a collar adjustable with an allen key, the collar fitting
partly over the fixed section of post, and partly over the bouncing insert.

The confusion is this: what's the collar for? It doesn't seem to
restrain anything - the bouncing insert is fixed to the spring, the
collar can't be moved up or down, and the collar doesn't interact with
the bouncing insert at all. Indeed, all it seemed to be useful for was
placing a stress on the seat post, which is presumably why it chose to
fracture at that point rather than anywhere else.

(OT, but H*****ds didn't have a 26mm seat post, so bonus points to
Decathlon which did. And I hang my head in shame at not patronising my
LBS but it was Easter Monday...)

R.

Richard composed the following;:
Some gentle bumps resulted in a seat departing the horizontal, rapidly
rearward. On inspection, I found the suspension post had fractured
(almost all the way from front to back) at the top of the fixed
section where there is a collar adjustable with an allen key, the
collar fitting partly over the fixed section of post, and partly over
the bouncing insert.

Should the insert bounce? Is the collar meant to hold the insert into
the fixed part, or should it clamp down the fixed part, which then holds
onto the insert? It's a litttle awkward to envisage from your
description ..

The confusion is this: what's the collar for? It doesn't seem to
restrain anything - the bouncing insert is fixed to the spring, the
collar can't be moved up or down, and the collar doesn't interact with
the bouncing insert at all. Indeed, all it seemed to be useful for
was placing a stress on the seat post, which is presumably why it
chose to fracture at that point rather than anywhere else.

Is it simply to add extra 'meat' to the fixed part which, from what I
can gather from your description, if it didn't have a collar or other
extra support might fail prematurely anyway? If it is, maybe it should
only be nipped up to stop movement, not tightened up as tightly as a
tight thing being done up too tightly, IYSWIM.

Is the collar meant to connect the spring to the seatpost, and the
insert is just a slider, to stop the springy bit moving in all
directions, only allowing movement in one plane?

Might help if you had a pic or two of the failure and components
together .. or a URL where there's a similar seatpost, and components of
such, on a website maybe ..

--
Paul ...
(8(|) Homer Rules ..... Doh !!!

Paul - xxx wrote:
Richard composed the following;:

Some gentle bumps resulted in a seat departing the horizontal, rapidly
rearward. On inspection, I found the suspension post had fractured
(almost all the way from front to back) at the top of the fixed
section where there is a collar adjustable with an allen key, the
collar fitting partly over the fixed section of post, and partly over
the bouncing insert.


Should the insert bounce? Is the collar meant to hold the insert into
the fixed part, or should it clamp down the fixed part, which then holds
onto the insert? It's a litttle awkward to envisage from your
description ..

Yes. :-) I'll dig it out of the bin and post a pic or two.

R.