Originally Posted by
grolby
Because aluminum frames with thin and flexible tubes have been manufactured in their thousands; see above for the example of the classic Vitus aluminum race frames, but there are dozens upon dozens of other examples. You see, part of actually knowing what you're talking about is having a historical and informational context against which stupid generalizations (like yours) can be tested.
As I said before, this is false, incorrect, a foolishly ignorant statement, however you want to put it. Most of the aluminum bikes that riders have experience with are road bicycles, typically race bikes. And most of these are built with large-diameter tubes because riders of these bicycles like a stiff frame. However, there are also aluminum frames out there built with different design goals in mind, and those... frames... flex. Sometimes a lot. Is this getting through, yet? Rigidity is NOT necessary for aluminum frame life.
No, I'm suggesting that you don't have the slightest clue of what you're talking about.
I am familiar with Vitus frames. A lot of them broke at the joints, quite likely due to excessive flex.
Simple fact is that aluminum has no fatigue limit which means the material is prone to cracking. Aluminum bicycle tubing manufacturers and aluminum framebuilders know this which is why they try to reduce flex in the frames. If you don't believe me try going to both Easton and Columbus's websites and look at the Al tubing they offer; all of it will be large diameter so flex is reduced in order to preserve frame life. That is not to say that a flexible Al frame is guaranteed to fail, just that there is a higher probability than one with stiffer tubes. The major builders don't take unnecessary risks, thus the stiff tubes.
You can choose to disbelieve these simple engineering facts, and insult me, but that won't change these basic truths.