In addition to unalloyed titanium, which is called commercially pure or CP, there are two alloys commonly used in the cycling industry today: 3AL-2.5V and 6AL-4V.
CP has half the strength of 3-2.5. A CP frame must be made heavier than an equivalent 3AL-2.5V frame in order to have comparable strength. Even most steels used in high quality frames have higher strength than CP.
6AL-4V tubes are not seamless. only heavy thickness tubes, 6/4 titanium has a greater tensile strength but it’s very hard to weld. they are rolled from a sheet and welded at the joint. What does that mean? It means that there is a potential failure point at the welded seam. Therefore we don’t recommend using this type of tubing.
3AL-2.5V titanium is an alloy consisting of 3% aluminum, 2.5% vanadium, and 94.5% pure titanium. The properties critical to bicycle tubing are best served by a high quality 3-2.5 seamless tube. Excellent fatigue life, property consistency, form-ability, and corrosion resistance are but a few of the reasons 3-2.5 is still the premier frame material.