Why a Titanium Bicycle Can Save Your Bacon

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Why a Titanium Bicycle Can Save Your Bacon
« on: 17 July 2017, 08:54:04 »
As you have been sitting at home watching the Tour de France participants battle through the Alps, I bet you are inspired to dust off your bike that's gathering dust in the garage and take it out for a spin! Hop on and realize you need a tune up and chain lube? So you took your trusty old aluminum frame steed down to you local bike shop and marveled at the new carbon fiber composite bikes available, many within your budget! You hand over your credit card as the clerk gleefully rings up your purchase (and throws in a free water bottle), reassuring you that your new "carbon" bike will make mincemeat out of those hills. You go for your first ride on your new baby, wondering to yourself; Hmmm, how did I ever manage to go through my life without this super-light hi-tech machine at my disposal? Then, as you reach down to drink from your new water bottle, you hit a bump on the tarmac and are launched into the air whilst your bike takes a tumble. Your pretty little head is safely protected by your helmet but unfortunately your brand new bike was not as lucky. Catastrophic failure and the front fork is broken, cracked, done in. Horrified, you return your new bike to the shop, where you are devastated to learn that the manufacturer warranty does not cover damage due to "user error".

What to do? Contact the manufacturer by email, post your complaint on Facebook, tweet out to your Pro-bicycling hero, receive nothing in return. Absolutely gutting isn't it? That's $2000 down the drain. You ruefully tell yourself that you could have had a great vacation in Aruba for that price. As usual, the answer lies in Materials Science. The  inherent nature of the "carbon" itself. Yes, carbon bikes are super light. But they are not damage tolerant. Herein lies the problem which most weekend warriors don't understand. Professional cyclists use these super-lightweight materials to gain advantages in terms of speed and therefore time over their rivals. Take a look at their bodies, they are typically unusually low in body fat and don't tend to carry excess muscle. You, the weekend warrior, are probably not built like these guys. Yet you bought a bike like theirs in the hope that you'd be able to fly up a mountain like you were climbing the Alpe d'huez in a polka-dot jersey! Kind of an unreasonable expectation, if you really think about it!

Sorry Ellie, where does Materials Science come in to it again? The "carbon" bicycle is a carbon fiber-reinforced composite material where, like all composite materials, mechanical properties are not isotropic. Like their aerospace counterparts, composite components for bicycles have low density compared to metallics but they are not damage tolerant. They also risk damage from UV light and moisture. The pros can overlook these drawbacks by simply swapping parts or changing bikes, no matter the expense, "carbon" bikes have become consumables in stage and criterion racing. The average weekend warrior will probably not want to spend $2000 every 6-12 months (although some bike snobs probably will). The rest of us mere mortals might prefer to put our money in a somewhat less risky material combination. Hence, the titanium frame bicycle is here to save our bacon (figuratively). Although titanium's density is about 2.5-3 times that of a composite, the combination of strength, modulus and toughness make it a much better long-term option. Titanium isn't affected by UV light and corrosion resistance is excellent. Pro riders do say that they prefer "carbon" bikes as they like the stiffer rides that composite frames offer but with strength only being carried in the major axis of the reinforcing fibers, the risk of catastrophic failure in a crash that occurs due to stress being applied normal to the major fiber axis is incredibly high. Whereas any time that you wipe out on your titanium frame bike, you can pretty much guarantee that nothing will happen to the bulk material, which are simply formed and welded tubes made from titanium sheet. Weakness might exist in the welds, yes, but the same is true of "carbon" bike components which are simply autoclaved and glued. Once cracked, or dented, composite components can never again carry the load as efficiently as they did prior to the damage, even if additional resin is poured to act as a "bandage", once broken, the fibers are broken forever. Whereas, in a crash, if there is any damage to a titanium component, the metal part can be re-formed and re-welded if necessary. Titanium can also be recycled - making it more environmentally friendly than leaving shards of resin and fiber all over the road.

Another thing worth mentioning is that there are various grades of composite that are available and cheaper is not necessarily better in this area. Titanium frame bikes tend to be for the most part Ti-3Al-2.5V (Grade 9) with a few additional pressed and machined parts made from Ti-6Al-4V(Grade 5). 3-2.5 is the most typical material for frame parts, since it has a better  cold formability than 6-4 but a higher strength than CP Grade 1 or 2. It's true that you could lift your lightweight "carbon" bike with one hand, but, it might not be around as long as you'd like to to be, especially if you are prone to crashing. You could still lift your titanium bike with one hand and rest easy in the knowledge that you could probably hand down your titanium bike to your children!

Writing: Eliana Fu
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