[Griff]

Originally Posted by HungLikeJesus

Here's a question for you weight weenies: why use titanium when aluminum is so much lighter?

Everything you never needed to know about frame materials. This is from the perspective of a touring cyclist, but that doesn't change the physics.

Steel vs Titanium
Look at the chart again. You'll see that identical steel vs titanium frames would be about equal in strength, but that the titanium frame would be about half the weight and half the stiffness.

Such a frame would likely have a whippy feel due to the reduced stiffness, especially in loaded touring applications. To compensate, builders of titanium frames use somewhat larger diameter tubes to bring the stiffness more into line with what riders like. This tends to increase the weight a bit, but by making the walls of the larger tubes a bit thinner, they can compensate to some extent, and come up with a frame that is still lighter than a normal steel frame.

Steel vs Aluminum
The situation with aluminum is even more pronounced. The "identical" aluminum frame would be 1/3 as stiff as steel, roughly half as strong, and 1/3 the weight. Such a frame would be quite unsatisfactory. That's why aluminum frames generally have noticeably larger tubing diameters and thicker-walled tubing. This generally results with frames of quite adequate stiffness, still lighter than comparable steel ones.