It's true that raw titanium costs about five to ten times as much as aluminum per pound, but bikes aren't that heavy. Nor is there a supply and demand relationship to consider, because people aren't exactly screaming in the streets for more titanium bicycles. So what's going on here? Are we being screwed over?
No, not exactly. The reason ti-frames are so costly has a lot to do with the technical and labor aspects of working with titanium. Because examining the full economy of titanium frame production will take more time than either of us is willing to spare, I'll give three special considerations that are unique to working with titanium. Hopefully that $10,000 for the Firefly custom you've been licking your lips over will make more sense after we examine some of that dull-looking metal's special needs.
1) Machining. This is a broad term that refers to cutting, drilling into, shaving, milling, reaming, tapping or doing anything that uses a tool to force away material. In bicycle construction, not only does metal have to go through a machining process to become a tube, but tubes have to be machined to fit together. However, titanium is hard, so you need extra-sharp tools that don't live very long and need a lot of muscle to operate, so the machinist has to be well-trained and coordinated. Titanium doesn't dissipate heat well, so the section touching the machining tool can overheat and become brittle, or oxidize, so the machinist has to spray liquids and work slowly. Titanium is springy (it has a high Young's modulus of elasticity, as the enginerds say), and sometimes chatters against cutting edges, so the machinist has to take extra care when clamping a tube down. And titanium spits off coils and metal chips that clog the machining area up, so the machinist has to pay attention at all times. Other metals, like steel or aluminum, are a lot less finicky.
2) Welding. All metals are tricky to weld; welding is a tricky craft. But what makes titanium extra tricky is that when it melts it becomes reactive with whatever oxygen is in the area. That reaction causes discoloration and makes the weld brittle. To avoid this, titanium welders flood the area they intend to heat with inert gas that will hopefully push away all the oxygen. This means, in short, that titanium welders need special tools and have to use special techniques.
3) Finishing. Sticking tubes together in triangle shapes is how you get the outline of a bicycle, but before it's ready to be ridden the builder has to make some adjustments. Metal deforms when heated, and sometimes moves around, so after the frame cools from welding a builder takes a number of measurements and compares them with the bike's blueprints to make sure the object desired is the object delivered. You can read more about that here. If the measurements don't match up, the builder has to bend the bike's tubes and file its dropouts to get them where they need to be. With steel, this is easy. You can bend steel tubes with a 2x4 and if you have to file something down you need not consider any special techniques. But as we saw earlier, titanium does not like to be filed. You can do it, but it isn't as easy as steel. Also, because titanium is both springy and strong, you have to give it a lot of effort to make a slight bend. How much more effort? Well, this is sort of hard to compare because titanium bike tubes have a different wall thickness than other metal tubes, but chemically speaking, if you have a tube of titanium and a tube of steel, the titanium will require about three times as much effort to make a permanent bend. The exact reasons for this have to do with a bunch of concepts like Hooke's law, Young's modulus, and Tensile's strength, but again, neither of us really wants to write/read a Ph.d dissertation on the physical properties of metal right now, so please just trust me that titanium doesn't bend well. Granted – once a titanium frame is finished, the high strength and modulus of elasticity means it won't dent or warp as easily as other bike metals when you ditch it in the weeds while screaming down a fire-road at twice the posted speed limit. Also, aluminum doesn't bend, it breaks. So if an aluminum frame is twisted, there's no un-twisting.
There are many other influences affecting the price of titanium bikes, but here I hope I've shown that titanium is hard to work with compared to other metals: it requires special tools, special techniques, and a specialized worker and all these things add to the final price of the build.
The real question is whether the 500-1000% markup between titanium and the other common bike frame materials is really worth it. What real advantage does a titanium bike have over a steel, aluminum, or composite frame? Perhaps we'll explore that in later posts.