There have been opinions expressed here about minimum safe stem quill insertion, but what about minimum seatpost insertion?
I recently bought the Haral frame on eBay made of Excel CSK tubing which has a carbon sleeve inside a thin-walled steel tube. This presents a problem with what sort of seatpost to use. The carbon sleeve starts approximately 80 mm below the top of the seatlug. A 26.8 post will go in only that far, so the inner diameter of the carbon layer is smaller, perhaps 26.2.
The seller says the post which came with the frame, which he hasn't found yet, was an American Classic 27.4 mm cut short to fit into the seattube section above the carbon sleeve. But it isn't clear whether this was original. Also not clear what post the frame manufacturer recommended. I could buy a 27.4 Kalloy Laprade and cut it to fit, but is 80 mm of seatpost insertion adequate? The frame is 55.5 to 56 cm ctc which is at the tall end of my range, so I'll probably have only about 50 mm of post exposed above the seatlug (not counting the post head). Does 80 mm insertion with 50 mm exposed sound safe? Does the thin wall of the steel tube increase the risk of the small insertion? Someone recently mentioned a very short Campy Record post from the early 70's. How long was that post and what would its typical insertion length have been?
I suppose I could use a post which fits inside the carbon sleeve and shim the section at the top of the seattube. Will any standard shim work for a 27.4/26.2 diameter?
Regards,
Jerry Moos