Originally Posted by Scooper

My problems with aluminum as a frame material are the very low elongation property of aluminum compared to steel or titanium, and the fact that most aluminum alloys don't have an endurance limit.

Elongation is the property of the metal that determines how far it can be bent before it breaks (brittleness), while lack of an endurance limit means that even a minuscule load, if applied enough times, will eventually result in a fatigue failure, often without any warning. Sudden, catastrophic frame failure can ruin your day.

Steel frames, OTOH, have higher elongation percentages and do have endurance limits, so failures are predictable instead of sudden or catastrophic. Because steel has endurance limits, repetitive small loads that aren't big enough to deform the material permanently (bend it) can be imposed on steel frames over periods of many years without failure, and if failure does occur it invariably does so with some advanced indication that it is about to fail (fatigue cracks, etc.).

For me, carrying a few extra ounces of weight in a steel frame is cheap insurance. New high strength stainless steel alloys like Reynolds 953 make possible thinner walled (lighter) steel frames that compare favorably with titanium and carbon fiber composite frames in terms of weight without compromising strength or durability, and without the low elongation (brittleness) of carbon fiber.

Just my opinion; I could be wrong.