Originally Posted by prathmann

Only aluminum bikes with large-diameter tubing are known for their stiffness. Earlier aluminum bikes built with standard diameter tubes so regular derailleurs, shifters, and cages could be clamped to them, such as the Vitus and Alan makes, had the opposite reputation - they were known for being comfortable and light, but too 'noodley' for many riders.

And so far I've only broken steel bike frames. My only aluminum bike is almost 30 years old and over 160,000 miles; which is more than that of the steel frames that broke. Yes, it'll break eventually, but so will steel bikes if ridden on typical road surfaces. Frames of reasonable weight will encounter many stresses in typical riding that exceed their endurance limit.

Originally Posted by BlazingPedals

Campag, you are arguing against a known property of aluminum. That's why aluminum bikes have a reputation for being stiff: if they flex, they will eventually fail and so they're designed to not flex. Modern alloys may go more cycles before failure, but they'll still fail.

I have personally broken two 6061 aluminum frames. The latest replacement frame is 7005, and while it has already lasted longer than either of its predecessors, sooner or later it too will fail.