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Is rubber buffer between seatpost and CF base necessary?



 
 
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  #1  
Old July 29th 04, 09:39 PM
TheBadger587
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Default Is rubber buffer between seatpost and CF base necessary?


In (I think) George Barne's instructions on how to set up a CD airseat,
he recommends putting a piece of rubber (out of an old tire tube)
between the seatpost/rail adapter and the seatbase to reduce stresses on
the cf seatbase. However, in John child's CF seatbase gallery (and
elsewhere) there is no mention of a rubber buffer. Is it a good step to
take to improve the lifespan of a CF seat, or does it just reduce a
seat's stiffness? (or is it both?)
thanks for putting up with my... 3rd post about the CF seatbase (coming
in the mail today, according to ups's tracking system.)


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  #2  
Old July 29th 04, 11:04 PM
S_Wallis
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Default Is rubber buffer between seatpost and CF base necessary?


The problem with putting rubber between the CF base and any of the
components that attach to it is that the bolts can never actually be
“tight”. They are just pulled down until the rubber is compressed.
This allows a little movement in the assembly and while it probably will
not cause a failure in this application, it is not ideal. If the rubber
is very thin, like a light duty bike tube, it will pretty much squeeze
down to nothing and not hurt anything. If it is thicker it can cause the
CF to try to deform around the hole into the rubber over time. This
tendency to “creep” is something to always keep in mind with plastics
and composite materials much more so than metals.
It is best to have all parts match up perfectly and have nothing between
them, and keep the bolts tight. In the real uni world, many components
do not match up perfectly and this may be the reason for the
recommendation. You can put the seat post/rail adapter against the seat
base and see if it contacts the surface well and not just in a few
spots, especially sharp corners. If you have the means to file or grind
off any sharp contact points, that is the best answer.

That’s my opinion on rubber, but I'm flexible.

Maybe someone else can give you a more helpful answer, like "yes" or
"no".

Scott


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  #3  
Old July 29th 04, 11:34 PM
john_childs
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Default Is rubber buffer between seatpost and CF base necessary?


I used some large smooth washers with rounded edges between the rail
adapter and the CF seat base. Without the washers the rail adapter
makes contact with the CF seat base at four pointy points. It's not
good to have all the forces on the CF seat base concentrated on four
pointy points like that. The washers spread that force out over a
larger area and avoid having the forces concentrated at sharp points.
The washers accomplish the same effect as the rubber inner tube pad.

Ideally the seatpost mounts would have the exact same curvature as the
CF seat base so there wouldn't be any sharp concentrated points of
contact. But the curvatures aren't the same so we need to do something
to spread out the contact area. The washers or rubber pad are two ways
to spread out and smooth out the contact area.


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