Bike Frame Materials: The basics
This entry was posted on February 28, 2012.
The material of your bicycle frame has a large effect on ride quality and ride feel. The type and quality of material also make up a large portion of the bicycle's price. The most common frame materials today are aluminum alloys and carbon fiber. Steel and titanium frames are highly popular, as well, but they enjoy more of a cult status with extremely dedicated followers. All frame materials have different levels of quality, and each material has its advantages and disadvantages.
Before we get into each material, it will help to go over some basic terms:
- Fatigue \fa*tigue"\, n: The weakening of a material when subjected to repeated stress or cyclic loading.
- Fatigue life \ fa*tigue laif"\, n: The number of load cycles required for a material fail.
Most of the larger companies use proprietary alloys (mixture of aluminum and other metals) to build their bike frames, and each manufacturer touts their specific brand and the way they use it. Aluminum frames can be more affordable than their counterparts because high quality alloys are easier to procure and manipulate into a quality bike frame.
The main advantage of Aluminum as a frame material is density, meaning for the same volume of material, aluminum weighs less than steel or titanium. This allows bike frame manufacturers to build fatter and, therefore, stiffer tubes that weigh the same or less than their steel counterparts. Another big advantage of aluminum over steel is corrosion resistance. You can ride aluminum in rain and snow and forget about it when you get home, while steel bikes take a bit more nurturing. The disadvantage? Fatigue life. As aluminum flexes and shifts, it fatigues and eventually hits its limit.
"Steel is real" is the mantra of every boutique bike builder and hardcore vintage and classic bike enthusiast in America. While some incredible racing bikes are still built out of steel today, it has lost a lot of popularity in that mainstream venue since the surge of aluminum and, more recently, carbon fiber. Steel has been used in the manufacturing of bicycles longer than any other material. From the early days of solid steel handlebars and Rene Herse to boutique builders today like Vanilla, Seven, and Serotta Cycles to name a few, the history is long and beautiful. Steel was originally used in bike frames, no doubt, because of its widespread availability and its long history of use in industry.
The big advantage of steel today is its strength and comfort. The disadvantage in the racing world that goes along with the comfort of steel is its lack of stiffness. Being denser than aluminum, steel frame tubes are generally smaller in diameter than aluminum. Using steel tubes that are as fat as many aluminum tubes used on bicycles would be too heavy for practical use. The thinner tubes flex more and are more comfortable to ride, but they are less responsive in race situations. Fatigue life of a steel tube is nearly twice that of aluminum, so steel bikes can last much longer under heavy use. As with aluminum, steel comes in varied qualities, from heavy core steel that has no place in the bike world (but is used in many big box store brands) to high-quality steel tubing designed for high-end bicycles. Price tags vary greatly throughout the range.
Titanium frames have enjoyed an even smaller cult following than steel. Titanium offers big advantages over steel in many ways, but it also has its disadvantages. Titanium is twice as dense as aluminum but nearly half as dense as steel. Fatigue life and tensile strength are Ti's big strong points.
Titanium can be extruded into long, thin tubes that are lighter, more comfortable and stronger than steel. Butted and swaged tubes offer a lot of customization in ride quality and responsiveness, making Ti an optimal choice for a custom-built bicycle frame. Cost is the main disadvantage of titanium. The process of extracting the metal is costly and energy intensive. Ti as a bicycle material is also more labor intensive. It requires more care and more time to cut and weld Ti tubing in a safe, lasting manor. There is virtually no way to build a budget Ti bike. You won't see these on the floor of your local department store.
Carbon fiber has become the frame material of choice for bike racers and many recreational riders alike. Carbon fiber is composite laminate made up of tiny fibers suspended into a resin. Carbon bike frames have many advantages and two real disadvantages.
Carbon fiber is extremely customizable. When carbon tubing is made there are many plies, or layers, of fibers that are placed in different orientations that offer different characteristics. Stiffness and flexibility can be manipulated on different planes of the same tube to offer huge advantages over all other materials. Carbon fiber is nearly half as dense as aluminum and much stronger for the weight. So a well-made carbon bike can be built stiffer, stronger and lighter than an aluminum, steel or titanium counterpart.
The biggest disadvantage with carbon fiber is flexible strength and fatigue life. The resin holding together the fibers of the laminate is a very rigid material that doesn't like to be flexed and bent. Too much flexing causes cracks and fissures in the structure and exposes the individual fibers which aren't so strong by themselves. This failure of the base structure can cause sudden, catastrophic failure of the bicycle frame. For these same reasons, carbon's fatigue life is rather low, giving a much shorter lifespan to a carbon fiber bicycle.
The other disadvantage to carbon is price. Carbon is the newest addition to the bicycle industry and is the subject of much research and development. While this RD spits out shiny new products and features, it also comes with the price tag needed to recoup those expenses.