Technology of Composite Bicycle Frames
The definition of technology is systematic treatment/application of knowledge to produce something (Webster’s1496). I will take this definition and describe the technology of making a bicycle frame. Composites structures are defined as : “...constructions utilizing admixture or blend or a compound of distinct parts or elements of various available materials to produce a resulting structure of the highest possible strength to weight ratio ...” (Moynihan ). For this paper “composite” will mean a plastic resin reinforced with structural fibers. In this paper I will be comparing composites against other methods of building bike frames.
First we will discuss the structural advantages of building a bicycle with composites. Using composites you are not limited to certain shapes as if you were using metal tubing. Most metal bike frames are tubes of standard sizes and standard wall thickness. With composites, you can differ the thickness of the wall of the frame. If you want more strength in one area, you just add more material in that area. By changing the wall thickness in composite layups, you will change the strength of your frame in a localized area. Metal tubing construction is mostly limited to constant thickness walls. Because of the constant thickness the metal bike frame will end up being heavier than it needs to be.
Composites do most of the things metals can do in a bike frame. Although, often the way you go about building with composites is different than if using metals. With composite construction a mold has to be built to form the required shape and then the fibers and resin are held in the mold to harden. With metal tubing construction, off the shelf tubes are cut to length and then fastened together to make the frame. Using composite construction you can build a frame with fewer joints than metal construction. Fewer joints give less chance of cracks starting.
Composite construction can end up being lighter than if you had made the part out of an equivalent metal. Weight savings of as much as half the equivalent metal are possible. The tensile strength of the composite frame can also be as much as twice the metal frame. It is also possible to have a composite frane that is both lighter and stronger than if you had built it out of metal.
Another point of interest is that composites are corrosion resistant. Metal frames must be painted to prevent corrosion. A chip in the paint on metal tubing will result in corrosion to the frame. Composite frames don’t have to be painted. If painted, flaking of paint is not a problem since the frame is naturally corrosion resistant.
Composites have a low thermal expansion rate compared to metals. Metals don’t maintain their dimensions as well as a composite over a certain temperature range. However some composites don’t hold up in low temperatures or in temperatures above 300 degrees F. Another negative...