Not really being a answer of the question, but, the most important aspect is not when or if it is breaking but HOW! I rather have a nice gentle steel frame brakedown so I got time to stop (I would have to be blind not to see damages to the frame before I start riding). While on a Al frame it says "snap" and if I happen to be riding downhill, well, ask the guy that finds you in some bush to call the dentist, you are going to need it.