Originally Posted by
prj71
Niner had a few frames in recent years that would crack. Jet 9 would crack in the head tube area and the Air 9 would crack in the bottom bracket area.
Back in the '80s, the San Rensho sale rep, showing off the latest frame iteration in the bike shop where I worked, said that the earliest version of that model of the frame had tended to crack near the shift lever braze-ons, so they beefed up the tube there, which resulted in some down tubes cracking near the bottom bracket. They then increased the tube wall thickness there, followed by some chainstays cracking. The latest version used upgraded chainstays, he said.
Edit: forgot to mention that those were steel frames.