Originally Posted by
cyccommute
If you were to use the same tube diameter and tube thickness, steel would definitely beat you up more in any haul than titanium. Steel is an incredibly stiff material. The only reason that steel bicycles aren't as stiff as aluminum and titanium frames is that the tube diameter is smaller so it flexes a little more. A steel frame with the same tube diameters as an aluminum frame would jar the teeth out of your head.
You are right on diameter but wrong on the stiffness. Steel is twice as stiff as titanium. Yield strength is about the same while the density of steel is twice that of titanium. Titanium frames probably don't need to be as large a diameter as they are but the tube diameter is a left over from the days when industrial titanium tubing was used for Ti frames.
Let me be more clear...you have misinterpreted what I wrote and were overly literal:
A steel frame isn't inherently stiffer or less stiff than a ti frame...the frame's stiffness will come from what a builder chooses to do with the materials. Aluminum is inherently less stiff/dense than steel, but Cannondale riders will tell you how stiff their aluminum frames are because of what is done with the aluminum (very oversized diameter). Sean Kelly's aluminum frames certainly are not stiff.
A compliant frame can be built from steel or ti - and a good builder will be able to build you a frame from a variety of materials.