Originally Posted by cb400bill

Opinions?

Originally Posted by dddd

The reason the frame cracked is because of the heat treating that was done to make the very thin tubing stronger (higher yield strength and higher fatigue strength), so it retains alignment and lasts longer during hard use.
However, heat-treated aluminum cannot be dented without introducing precurser cracks, and is thus no longer malleable.

Any welding done after heat-treating will return the metal to it's original, weak state.
If this frame doesn't use butted tubing, there is some excess of strength along the mid-sections of each tube, and the heat treating was done firstly to strengthen the ends, where the stresses are highest. Whether or not the middle of each tube is thick enough to retain sufficient strength after welding would be very hard to calculate however, and cracks anywhere in a heat-treated frame tend to spread rapidly in brittle (sometimes spectacular) fashion.
I've seen and heard Cannondale frames snap in two, with a bang, the metal is that brittle!