Here's an excerpt from an interview I did with an Italian mountain bike magazine a few years ago. Since it was never published in English, and probably no one from the US saw it, I am posting a bit of it here; I'll post more of it later.
Keep in mind that I was trying to communicate in language designed for non-English speakers. Of which, I can relate--I often feel like a non-English speaker.
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“Once titanium was considered the most valuable material, today aluminium [and carbon] is chosen also for the most expensive bikes. But the peculiarities of titanium are unique. Why has it loosen its appeal?”
There is a long list of reasons that titanium is an excellent material out of which to build bikes. A partial list includes:
· Frame’s strength-to-weight ratio: titanium alloys have the highest ratio of any bike frame material. This include carbon fiber, too. (I can explain why, if you are interested.)
· Tunability of the ride characteristics: titanium allows for a wide range of tube options. (If the builder is willing to invest significantly in materials; see below for details)
· Durability or fatigue life: 3-2.5 has the highest fatigue life of any frame material. This means 3-2.5 builds the toughest frames. This is particularly valuable for hardtails and dual suspension frames.
· Durability in real world use. Because titanium is so tough, it holds up better than other materials in daily riding conditions. Steel and aluminum must be painted. Aluminum is very soft so it dents—and therefore fails—easily. Carbon fiber is has poor impact resistance so it is easily damaged.
· Corrosion resistance: steel rusts, aluminum corrodes. Carbon is susceptible to UV degradation.
· Customization: Titanium—when used correctly—offers the most design flexibility of all frame materials. Carbon must be molded. Aluminum and steel offer tube sets in only a few options—by brand.
· Overall Value per Euro: because of all these factors, I believe that 3-2.5 titanium alloy—when applied properly—offers the best value per Euro invested.
Seven Cycles brings even more reasons to invest in a titanium bike. These include:
· Tubing quality: Seven uses the tightest certification tolerances in the bike industry. This includes grain structure, strength, straightness, finish quality, and more.
· Tubing variety: we have over 20 tube starter stock sizes from which to apply to tube sets.
· Rider specific tube sets. Because of our unique tube butting process and frame builder system, we make the tube set for each rider, one at a time. On two tube sets are identical. We can do this to a greater extent with titanium than any other material.
· The extent to which we customize. We customize just about everything including the ride characteristic, handling, options, performance, and more.
All of these elements combined provide a better overall riding experience.
So, you ask, if there are so many reasons to build—and buy—titanium bikes, why are they not more popular? This list is long, too. It is also complex. The key issues are high cost, requirement for significant commitment, high level of complexity, and poor application.
To help express this list as succinctly as possible, it may help to put it in the steps required of building a frame. These steps may seem excessive, but cutting corners with titanium means the frame will almost certainly fail. Titanium is much more sensitive to processing and contaminants than any other bike frame material.
Some of the main steps in building a titanium frame include:
1. Choose your titanium alloy
· 3-2.5 alloy: is most popular in the US for frame building. It offers the highest fatigue strength of all titanium alloys and is most easy to source.
· 6-4 alloy: is used in small quantities. The cost is high and fatigue life is lower. Tube options are extremely limited. The purported benefits of 6-4 titanium is marketing buzz.
· CP: is pure titanium. This is not used so much anymore in the US. It is very weak—about the strength of 6061 aluminum. Most of the titanium frame failures in titanium are built from CP.
2. Choose your quality
· Country of origin. This is a critical decision. The highest quality titanium is still coming from the US. The second and third most common sources are China and Russia. Both of these sources are low cost with very limited tube options, property inconsistencies, and
· Controlling processing variable. This is affected dramatically by country of origin. However, even in the US—or within any country—there are many levels of quality and strength—just as there are with steel and aluminum frames.
· Grain structure. This is determined by processing. Grain structure is critical in titanium in order to optimize the fatigue life and strength. However, you cannot see grain structure by looking at the material; all titanium may look the same but it does not all perform the same. Grain structure can effect fatigue life by 50% or more.
· Certification standards. In the US there are 3 main classes of ‘certification’:
1. Aerospace: Certified to ASTM B-338 specification. Each lot of tubing receives extensive testing and paperwork. We can track any defect back to the original source.
2. Sports Grade: Certified to less stringent specification; reduced testing. This is the most common type of certification for bicycle frames.
3. Surplus & Scrap: No certification or test reports. Use this material in bike frames at your own risk. You cannot know the grain structure or other processing variables.
Seven has created our own certification process that is most closely matched to aerospace certification.
3. Machining the frame
Titanium is unique in bike frame materials in its difficulty in machining. The most difficult elements are:
• Difficult to machine; tough and “gummy”. The part moves and flexes away from the cutter.
• The material fuses to the cutter and thereby makes cutting more difficult and cutter failure more common.
• Work hardens—the more you cut it, the more difficult it is to cut; degrades cutters quickly.
• Difficult and expensive to caste and forge. This is why you do not see forged dropouts or other small parts. All of those parts are machined for solid stock. This is expensive and time consuming.
• Strong alloying tendency: interacts with cutters, oxygen, oils, etc. You have to be very careful not to contaminate the material during the machining process.
4. Welding the frame
Titanium is the most delicate and difficult bike material to weld:
• Oxygen contamination. Titanium loves to alloy with its environment. Must be welded in an inert environment. This is time consuming, expensive, and difficult.
• Contamination: even finger print oils have an extreme negative effect on the strength of the weld.
• Requires customized welding machines. Titanium is a specialty metal so no prefabricated equipment exists for welding it properly. This takes trial and error and a lot of experience.
• Requires high level of welding skill. For Seven, it takes 1 year to train a welder from the beginning. Welding titanium bicycle frames requires two competing skills at once:
1. Weld speed: because titanium is a poor conductor of heat, it distorts a lot when welded. The faster you weld, the straighter the frame will be.
2. Weld bead accuracy: Not only do we want the weld to look nice, that nice even weld is also required in order to avoid stress risers that lead to premature failure due to notch sensitivity.
5. Aligning the frame; making sure it will ride straight and true
• Titanium’s high strength means it is very difficult to ‘cold set’ or align.
• Titanium work hardens. This means that as you bend it, it gets stronger and more difficult to bend. You have to bend it correctly the first time or it gets more and more difficult to make correct.
Because of all these challenges, not many builders want to invest what it takes to do a good job. And some builders address these challenges by oversimplifying their importance. They use one tubeset sourced from Russia or Asia; the make only a few sizes as fast as possible while cutting corners to save money. Unfortunately, this hurts the reputation of titanium.
However, Seven has found that—by following the procedures we have developed—the resulting bike is well worth the investment; it rides better, last longer, and is more fun.
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