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.)
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
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.