Dave,
The down tube near the bottom head lug is said to be where most stress is on the frame tubes. The DT should be the most sound tube then. Any steel tube should give one plenty of notice before it brakes completely. I know of a guy who rode his bike another two miles home after the DT completely broke on his frame. Bent the 1" tob tube, but he still rode it, like a fool.
If you have a bike (lugged steel) that is slightly bent at the DT, just keep an eye on it. If something developes you will have plenty of time to deal with it.
Brian Baylis
La Mesa, CA
As long as one of the currents topic of discussion is frame damage, I have a question for the frame experts: damage to which of the three tubes in the main triangle of any lugged steel frame (vintage bike, of course) is the most significant in terms of safety and in terms of the probabilty of being able to predict the likelihood of failure?
Dave Van Hook
Hershey, PA