Originally Posted by
Andrew R Stewart
Independent of frame design AL is a weaker material then steel, more flexible and (here's the important aspect) has a limit of fatigue cycles before failure. Hence an AL frame, to be signed off on by the liability people, needs to be stiffer then a steel one. A stiffer frame won't flex as much so the fatigue limit won't be achieved as soon. One way to do this is to use larger diameter tubes (a tube increases in twisting resistance as a square of it's diameter but linierly with it's wall thickness). This is why AL tubed bikes usually are larger diameter tubed then a steel one. (And our view of "bigger is better" feeds right into this as far as the marketing goes).
This nuance, material characteristics as opposed to design, is not well understood by many and not explained by most who do know the difference. Andy.
There is a lot to like in all the materials. I owned an aluminum bike in 1976 until it got stolen. After getting back into the sport, my bikes are now steel as durability and cost are more important. Some people must own sport cars, if your one of those then go for Carbon or high end aluminum. If not then take a look at steel touring bikes, a lot of my steel bikes are 20 to 30 years old. And that is fine if the bike was quality to begin with. A quality bike will ALWAYS be a good bike, no matter the material.