Framing Support Photo by by Mike Atwell Titanium frame cutaway reveals tubing construction. There are many materials to select for bike frames. Typical, mass-produced cycles use Chrome-Moly (CrMo) - a chromium steel which is inexpensive and resists rust moderately well (see the spoke section to read about another chromium steel - stainless steel). Increasingly, aluminum alloys are being seen as a steel alternative for frame material. But the true bike enthusiast (meaning one with an unlimited wallet) will chose titanium as the premium construction metal. Photo courtesy of Cherry Bicycles Jim Cherry III welds a titanium frame. Titanium is a very peculiar metal for which there is only limited applications. Where it works well is in applications that require a high degree of corrosion resistance, and applications where elasticity with a high degree of fatigue resistance is necessary - such as springs. Which brings us to the bicycle frame. Some builders believe that the bicycle frame should be stiff enough to be energy efficient but compliant enough to be comfortable to ride. To a large extent frame flex, particularly in a vertical axis, is the suspension of the bicycle. So, believing that it is ok to allow the bicycle frame to have some give to it, the material that you build the frame out of should have some fatigue strength. Look inside any racing engine and its a good bet you'll find titanium valve springs. For more information about the materials used in the bicycle industry, check out this web series by Scot Nicol: Metallurgy for Cyclists Narrative courtesy of Cherry Bicycles