Titanium alloy bicycle
Titanium is perhaps the most exotic and expensive metal commonly used for bicycle frame tubes. It combines many desirable characteristics, including a high strength to weight ratio and excellent corrosion resistance. Reasonable stiffness (roughly half that of steel) allow for many titanium frames to be constructed with "standard" tube sizes comparable to a traditional steel frame, although larger diameter tubing is becoming more common for more stiffness. Titanium is more difficult to machine than steel or aluminum, which sometimes limits its uses and also raises the effort (and cost) associated with this type of construction. As titanium frames are usually more expensive than similar steel or aluminium alloy frames, the cost puts them out of reach for most cyclists.
Titanium frames typically use titanium alloys and tubes that were originally developed for the aerospace industry. The most commonly used alloy on titanium bicycle frames is 3/2.5. 6/4 is also used, but it is more difficult to weld, make tubes of, and machine. Often, the tubes are of 3/2.5 while dropouts and other peripheral sections are made of 6/4. Experimental frames have been made with commercially pure alloys, but these proved less durable for the active riding intended for frames of this cost level.
