The joints for the fork blades into the crown, the steerer into the crown and the lower head tube joint are the most stressed places on a bike. Bumps and braking apply a lot of stress to that area. Stress risers need to be minimized there and not overheating the metal during brazing is critical. A break in the fork or lower head joint is not so safe no matter what material used in making the frame.
Oddly enough IME it's not the most common place for break to occur in steel frames. I've seen more cracks in the seat tube just above the bottom bracket and one of the chain stays at the BB. I think overheating the metal during brazing is common there due to the mass of the BB shell needing to be heated to get full flow of the brass or silver throughout the joint. If you sight down along the seat tube or down tube to the BB shell, you can often see some distortion of the tubes from overheating. When you are standing to sprint or climb, you're putting a large tension load on the seat tube-BB shell joint as well as a bending load. The flex of the BB shell also puts a bending load on the chain stay- BB shell joints. It'd be interesting to rig some bikes up with strain gauges and see what the measurable differences in frame flex are; in the interest of discussing "planing" (a term I react to negatively for some reason) it would be interesting to see if measured dynamic flex matches the subjective impressions that lead to preferring one bike over another. -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
