Clockwork '91 - Shim for 27.2 seatpost?

[toontra]

Orange have the spec. for a '91 Clockwork seatpost as "27.2 + shim". That's what I'm using. Can't remember where the shim came from or what size it is but seems to work - the seatpost is 27.2. Without the shim there isn't enough grip to keep the post secure.

I got into trouble touring in India when the shim (doesn't have a top rim) got shoved down the seat-tube when building the bike up in sweltering heat in Chennai airport!

What I'm wondering is - why a shim? Why not just e.g. 27.4, 27.5, etc?

Thanks for any enlightenment!

 

[minor_LEGEND]

Great question. My 93 Clockwork is 26.6.
The speccing of the actual post may be down to the availabilty of correct size seatposts and the inside diameter of the frame tube. I have worked for a frame builder, depending on the gauge of tubing wall thickness it may be that the exact size of seatpin is not actually available or readily available to Orange at the time. So a shim may have been used with a more common size seatpin. You could always get the inside of the seat tube checked for size by a good bike shop using a sizing gauge (not verniers). failing that, get a nicer shim machined up for your bike/post with a retaining lip added on.

 

[toontra]

Thanks for the reply. Yes, I guess that's the only sensible answer. Strange that they would make a frame with slightly non-standard seat-tube though.

Might see if I can borrow a slightly larger seat post & see if it works or, as you say, sourse a better shim.

 

[minor_LEGEND]

It's not about making the frame non-standard. If by speccing the frame tubes to get the bike to ride/weigh in a certain way or even if the tubing manufacturer ran out of stock or a change was made mid-production.

The proper tool to establish the frame I/D for a seat post is like a long steel cone with the relevant post sizes marked on it in a gauge format. You can try a vernier caliper but it isn't always right. Is it possible your bike has been given another incorrect post with shim at some stage?

 

[brocklanders023]

Re:

Never seen a pre 1995 Clockwork with a shim? Think mine have always been 26.8 or 27.2?