I purchased a '85 Bottecchia frameset as a retro reclamation project. Last night as I was putting the finishing touches on the build (Campy and Modolo), I tried unsuccessfully to insert a Thomson 27.2 seatpost into the seat tube. I measured the ID with a pair of calipers and came up with 27.2. I then re-lubed the post and tube, but the post would not insert more than a couple of inches. I also tried a American Classic 27.2 without any luck. Any chance that C&V Bottecchia owner could provide some insight? Does anyone know if this vintage Bottecchia seat tube is actually 27.0?

What size frame and what tubing? My 1972 23" (58.5cm) SL frame is 27.2 but 25" frames are SP and usually 27.0. By the mid 80's there were many more tubing options and smaller increments between frame sizes so it would be hard to generalize.

It is 22" Columbus Aelle (Tretubi). Kinda near the bottom of the Columbus hierarchy.

My '86 aelle tubing bottecchia takes a 27.2mm seatpost, and it's 54cm.

Ok, I'll go out on a limb here so somebody correct me if I'm wrong but I have the following specs for the seat tube thickness:

SL 0.6/0.9
Aelle 0.8

So if the outside diameters are the same and SL uses a 27.2 and assuming that it's the 0.6 value that at the top of the tube where the post goes in, then an Aelle frame should use 27.0.

That make sense to anybody?

edit: Just another thought - the standard O.D. of the seatpost is 28.6mm - so if, for an SL frame, we subtract 1.2mm (0.6mm x 2) then we get 27.4. That would mean the seat post should be 0.2mm smaller than the measured I.D. of the tube which again would point to a 27.0mm seat post size for you Aelle frame.

I'll shut up now so somebody can tell me I'm all wet.

I think you're right. Of course, I didn't do any of the math, but simply plan to try a 27.0 post and see if it holds. Thanks!

Actually, Aelle typically takes 26.8mm posts once go to the next size below theoretical [28.6 -(2 x 0.8) = 27.0]. However, it was not uncommon for manufacturers to ream Aelle frames for a 27.2mm post so that they only had to stock one seat post size.

The question is whether the tube has been reamed for 27.2mm or not. You say a 27.2mm post inserts a "couple of inches". Normally an oversize post will not insert below the bottom of the binder slot, which is typically not 2 inches long. If it is going past the bottom of the slot, it sounds like it was reamed, but not very deeply. The other clue is to look at the sides of the binder slot for parallelism. Putting a 27.2mm post in a frame meant for a 26.8mm post will open the slot by about 1.2mm at the top. Conversely, putting a 26.8mm post in a frame meant for a 27.2mm post will cause it to be noticeably pinched, by about 1.2mm, at the top of the slot.

Doh! Guess that's why I wasn't a math major.