Spokesman Bicycles

“Once giants lived in the earth, Conan. And in the darkness of chaos, they fooled Crom, and they took from him the enigma of steel. Crom was angered, and the earth shook. Fire and Wind struck down these giants … but in their rage, the gods forgot the secret of steel and left it on the battlefield. And we who found it are just men – not gods, not giants, just men. The secret of steel has always carried with it a mystery. You must learn its riddle, Conan. You must learn its discipline. For no one, no one in the world can you trust – not men, not women, not beasts … this you can trust.” – Conan’s dad, from the film “Conan the Barbarian.”

Bicycle framebuilders have known about the secret of steel for a long time. In fact, steel has been used to build more bicycle frames than any other material. It has also been used about 50 years longer than any other material currently in use. In this second installment of our six-part series on frame materials, you’ll learn something about where steel comes from, and more about its advantages and disadvantages in bicycle-frame fabrication. But first, I’d recommend a re-read of the first installment of the series to familiarize yourself with the terminology.

Steel is made mostly of iron whose atomic symbol is Fe, from the Latin ferrum – and that’s where the term ferrous comes from when we refer to ferrous and non-ferrous materials. As you may have guessed, steel is a ferrous material, and aluminum and titanium are non-ferrous.

Iron is the fourth most abundant element in the earth’s crust, so in the near future we probably won’t be running out of the material that’s used to build steel bikes (chromium and molybdenum are different stories, however). Iron rarely occurs as a chemically pure metal, except in meteorites. On this planet, it’s found in various forms, among them magnetite (Fe3O4), hematite (Fe2O3), siderite (FeCO3), pyrite (FeS2) … and many other forms that end in ‘ites.

How do we get from iron to steel? We add and subtract a couple of ingredients while its molten, and voilà, steel (actually it’s a very involved and evolved process involving exothermic reactions, but we’ll save that for the extended-play version of this article).

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Good morning … afternoon … evening (circle one), class. Today, we are going to study aluminum. What we learn today will be based on the knowledge you’ve already gained during our two previous sessions. Did you all get a chance to review the first lesson – an overview? How about the second, on steel? Good. This one on aluminum marks the halfway point of our six-part series.

Aluminum as a frame material has increased dramatically in popularity over the last decade. In the early 1980s, aluminum bikes were a novelty, only available from a small, select group of high-end manufacturers. Then, in 1982, Cannondale jumped on the scene and began to push the material downmarket. Today, almost every medium-to-large manufacturer has at least one aluminum bike.

Furthermore, there’s plenty of material for them to use – aluminum is the most plentiful metal in the earth’s crust. And except for magnesium and beryllium, it’s also the lightest structural metal. A primary source of aluminum is the ore bauxite, named for the town where it was first discovered – Les-Baux-de-Provence, in France. The ore contains hydrated alumina (Al2O3*2 H2O) with impurities of iron and titanium oxides. Sounds like one-stop shopping for the bike industry’s metal requirements, eh? It’s not really, as we have better sources of titanium and iron ore.
Making Aluminum into Tubing

The actual process that changes the aluminum we find in the earth’s crust into a tube suitable for building a bike or lawn chair is complex, ugly and energy-intensive. It’s appropriate that the most important process for getting from bauxite to aluminum is called the Bayer method, because studying it will give you a headache…. It takes about 9 kilowatts of energy to produce a pound of aluminum – far above what’s required for steel. And although the production of recycled aluminum takes less than 5 percent of that amount of energy, virgin aluminum is needed to make wrought products – those that are rolled, extruded, or drawn.

A number of different alloys are produced using raw aluminum. For bicycle fabrication, the resultant wrought aluminum products commonly use a four-number designation system. An example of this would be the venerable 6061 alloy. (See “Aluminum alloys” for other examples.) Cast aluminum alloys use a three-number tag, a period, then a fourth number. Both wrought and cast alloys use another number that comes at the end: the temper designation. No doubt you’ve seen the T4 or T6 condition listed after some of the alloys: 7075 T6 or 2024 T4, for example. It describes what cold work, heat treatment and aging processes (if any) the material has been subjected to.
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The Titanium Development Association calls titanium “the material of choice,” and there are a lot of people in the bike industry who would agree. This, the fourth part of our metallurgy series, is about that mysterious and expensive metal, titanium. Its reputation within the industry is excellent: light weight, super strength and fatigue life, a magical ride … and a heavy price tag, to boot. So let’s find out what the physical characteristics are that give titanium such an enviable reputation.

Titanium is not as rare as you might guess – it’s actually the fourth most abundant metallic element in the earth, after aluminum, magnesium and iron. In fact, there’s a lot more titanium in the earth’s crust than there is chromium or molybdenum, two of the essential ingredients that accompany the iron used for steel bike tubing.

Density and Other Properties

As we learned last time, density is the giant feather in the property cap for aluminum. This is an area where titanium also shines, and although its density is almost double that of aluminum, it’s only 56 percent as dense as steel.

Our second property is stiffness, or Young’s modulus (E). The titanium that you find used in a majority of bicycle frames has an E of around 15 million pounds per square inch – approximately half that of steel. This means that steel and titanium are roughly comparable when it comes to the stiffness-to-weight ratio. Previously, we learned that the stiffness of a frame depends on design and the properties of the material used. The same goes for titanium – you can provide a flexible or a stiff ride, depending on execution. Because of the relationship between titanium’s high strength, low density and moderate modulus, most fabricators choose tube diameters that provide a supple, shock-absorbing ride. To push titanium down into the realm of the super light, the modulus becomes a problem, because then the frame gets too flexible. In this case, I’m talking about frames that weigh in the neighborhood of two pounds. Building ultra-light frames is not an easy task in any material … including titanium.

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If you’ve followed parts one through four of this series on bicycle metallurgy, you’ve learned a lot about the physical characteristics that are important to consider when designing aluminum, titanium or steel bicycle frames. This installment takes a step outside the realm of metallurgy, and looks at the use of carbon-fiber composites in bicycle frame applications.

The Wonderful World of Composites
It’s common to use the terms carbon fiber and composite interchangeably, even though all composites are not carbon fiber. For example, both plywood and concrete are composite materials. The term composite refers to combinations of materials that result in enhanced properties not provided by the materials alone (concrete is a composite of cement, sand, gravel and water; Cheeze Whiz is air, artificial flavors and artificial colors).

In scientific terms, composites are generally acknowledged as those materials in which either particles, short fibers or long fibers are dispersed in a matrix. In the case of the Duralcan metal matrix composite that is found in the Specialized M2, aluminum oxide whiskers are dispersed in a 6061 aluminum matrix; while advanced composites – the types used to build bicycles – have continuous fibers embedded into a matrix (typically epoxy).To qualify as an advanced composite, it is generally thought that the fibers are continuous, greater than 50-percent fibers by volume, and the fiber has mechanical properties superior to fiberglass. Fibers can be carbon, Kevlar (a.k.a. aramid), boron, ceramic, silicon carbide, quartz, polyethylene … and probably others that I’m not aware of.

A Simple Lexicon

Here’s a simplified explanation of how terms will be used. A fiber is a single strand of reinforcing material. A bundle of parallel continuous fibers are bound together with a glue, or matrix. A single layer of this matrix is called a ply, and multiple plies are laid up to form a laminate. The plies can be laid up in various angles to produce different characteristics of the laminate. If you’ve forgotten about the other terms used in this series – like tensile strength and elongation – re-read the first installment of this series to reacquaint yourself with those terms, because they’ll be essential to our discussion.

The Numbers Look Good

If you look at the numbers that carbon fiber can boast, your initial thought might be that it’s crazy to build a bike out of anything else. But you astute students of the School of Bicycle Geekdom already know that numbers are not the only thing to look at – you need to check out the fine print. And get this: With carbon fiber, you need to throw most of what you’ve learned out the window.

Yes, it’s true that the potential for composite frame materials is tremendous. Unfortunately, the results of some composite bicycle-frame projects have been less than satisfactory. There are reasons for the high failure rate that composite frames have endured, but the fault is not that of the material. I know you may find this hard to believe, but sometimes even rocket scientists make mistakes. The situation is similar to what happened with titanium in the 1970s. Teledyne made some frames that failed, not because the material was bad, but because the design was bad, or the execution of the design was bad. Similar things have happened with composites, and the image of the material is not as good as it should be.

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You probably thought that with this installment – part six of our six- part series on bicycle metallurgy – we’d be done with the subject. You were wrong, and you should know me better than that by now. I’ve added a seventh part, because there is too much remaining to discuss. And because I’m having too much fun doing it….

This time we’ll start to talk about exotics: those materials that we didn’t include in our coverage of aluminum, steel, titanium and carbon-fiber composites. The final episode of our series will have more about these exotics, plus a wrap-up and maybe even a quiz: I’ll present you with some materials that have fantastic “numbers,” and you can try to determine what they are, and why they would stink as a bicycle material.

Thermoplastic Composites

The previous installment of this series covered the subject of carbon-fiber composites (it’s not a metal, but we explained that last time). What wasn’t mentioned or covered – on purpose, I didn’t want to confuse the issue – was the distinction between thermoset and thermoplastic composites. The carbon-fiber composite bikes that you’re used to seeing are of the thermoset variety. A newcomer on the scene is thermoplastic composite. The difference between how the two are fabricated is analogous to the difference between bread and chocolate.

The process of making a structure out of thermoset composite goes something like this (breadmaking procedure in parentheses). You mix up some ingredients (flour, water, yeast); put them in a mold (bread pan); apply heat (oven); and a chemical reaction occurs (yeast reacting).Voilà, Wonderbread. There’s no turning back from this point. You can’t re-melt the bread and start over.

Thermoplastic composite construction involves mixing ingredients, then heating them up until they go through a phase change (that is, melt). To get your frame, make sure that the material freezes into the shape you want, but if it doesn’t, you can actually re-melt and re-mold it. (The number of times you can do this without property degradation depends on the material you’re using.) And apparently – unlike the outgassing characteristic of the themoset process – you won’t get much smell when this melting process happens. The material is also supposedly capable of being recycled, both by remolding or grinding and putting into a new mixture. So, because of its ability to be reformed and recycled, and the claim that is doesn’t emit nasty smells, some people are calling it a green material.

The only incarnation of this technology in our industry that I am aware of is the Yeti bike, made in conjunction with Kaiser Aerospace and Penske.A very important attribute of the thermoplastic materials is that the impact resistance is much better than with thermoset materials. Epoxy is a relatively brittle material, and brittle is not your friend in a bicycle. A negative attribute of thermoplastic is that it is hard to bond anything to it. Given the past history of composite structures, and the quantities of little bits that you need to bond to bicycle frames, this can be a formidable hurdle.

Magnesium

Imagine a metal with half the density of aluminum, strength better than 6061, and elongation around 10 to 11 percent. I’m describing a magnesium alloy here, currently being tested by Easton. While magnesium is not normally known for its ductility, Easton says the material looks promising with those 10 to 11 percent elongation numbers. Although the modulus is low, in the range of 6MSI, that really shouldn’t be an insurmountable problem. Aluminum has a relatively low modulus, but it doesn’t mean an aluminum frame can’t be built stiff. The same will hold true for magnesium, in fact a lower modulus would be welcome in the eyes of many.
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The end is nigh. This is the seventh and final part of our six-part series on metallurgy as applied to bicycles; obviously, we’ve extended the series, but this is the final installment – I promise. In this finale, we’ll finish detailing exotic material, and then give you a mystery material on which to chew (cerebrally, that is).

Aluminum Lithium
I can see the ad guys go crazy with this one: “Cure for manic depression! Try the new lithium bike! Feeling psychotic? Lick the top tube!” That’s right, lithium, as in the drug used to treat manic-depressive psychosis, is also used to enhance the mechanical properties of aluminum alloys. Actually, the lithium used as a drug is lithium carbonate, a derivative of metallic lithium.A look at “the numbers” for lithium aluminum alloys reveals some extremely impressive claims – among them high strength and stiffness. So why don’t we see any lithium bikes out there? My attempts to find out more about alloys with lithium were met with lots of secrecy, misinformation and contradiction. It turns out that lithium aluminum alloys have been around for many years, but not much has made it into bike tubing – or many commercial applications at all, for that matter.

For those who have to work with lithium in its metallic form, it’s more likely to cause manic-depression than it is to cure it. You see, lithium is a pain to work with. Lithium and aluminum together have even more pitfalls. Minute amounts of lithium can cause contamination in a processing facility. Lithium is unstable … and it loves oxygen. So you need to extrude it more slowly, and heat treat it longer.

The heat treating is critical … and easy to screw up. If you heat treat for too long, or at too high a heat – even by a small amount – the lithium can oxidize; then you’re left with a soft, almost pure aluminum. Since the alloys have only about one or two percent lithium in them, it doesn’t take much to make all the lithium go away. And the processing requirements and potential problems for lithium all mean one thing: expensive.

Although we can’t use pure lithium to make a bike frame, check out how it compares with other metals. Lithium is number three on the periodic chart; it’s the lightest of all metals; and far less dense than beryllium. Beryllium and magnesium have two thirds the density of aluminum, which is two thirds the density of titanium, which is half the density of steel. Wow, that’s a lot of fractions (they’re approximate, but close). You can see why these materials are enticing.

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DOUBLE, TRIPLE OR COMPACT – WHAT’S BEST FOR ME?

With the growing popularity of Compact Cranks, cyclists have a myriad of gear choices to choose from. Here is some general guidelines to help with your gearing decisions.

First, consider the terrain you ride in most often. Are you in a hilly environment with lots of climbing, or on more flattish, rolling terrain? You want your gearing to mesh with where you ride.

Second, what are your cycling goals, fitness and ability levels?

Here’s a comparison of setups:
(Based on 12-25 rear cassette)

STANDARD DOUBLE (53X39 tooth chainrings)
For the seasoned, fit cyclist or racer who has the strength to push bigger gears on climbs and will use a big gear for sprinting.

COMPACT DOUBLE (50X34 tooth chainrings)
Use of a Compact can run the gamut of levels of cyclist. A seasoned, fit rider that desires easier gearing for climbs, one who is transitioning from a Triple, or a newer rider who is attracted to lighter, simpler Compact setup.

ROAD TRIPLE (52x42x30 chainrings)
Most entry-level cyclists should purpose a Triple, which offers high gears for speed and very low gears for easier climbing. Also for a relatively avid, fit cyclist who rides in steep hills and wants to be able count on that “bailout” gear. NOTE: Most entry-level to mid-range stock road bikes are outfitted with a Triple.

Hopefully this helps de-mystify the topic of gearing and help you better select what setup works for you.

For more detailed information visit the following webpage:
http://sheldonbrown.com/gears/

Stop by every 1st Monday and 3rd Tuesday of every month to learn how to work on your bike