Originally Posted by vik
AL tubes are generally larger diameter and thinner wall thickness than a narrow steel tube. That's why they are more easily damaged and are lighter than a comparable steel frame.
If AL bikes had bigger tubes and thicker tubes they would be much heavier than steel bikes - which is not the case.
I cannot claim I have measured aluminum or steel tubes, nor am I interested in measuring them. Instead, I got my information from a recent article in "Adventure Cyclist" (Feb 2007 issue, page 46), by Sheldon Brown. Putting this information into context, I will provide a couple lead-in sentences:
"...The "identical" aluminum frame would be one-third as stiff as steel, roughly half as strong, and one-third the weight. Such a frame would be quite unsatisfactory.
That's why aluminum frames generally have noticeably larger tubing diameters and thicker-walled tubing."
(italics my own, to indicate which sentence contains the information I provided in the earlier post.)
A great all-around article, BTW. I learned a lot.
P.S. I hope it's ok to quote sources directly as long as I gave them credit, like in academia.