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1 Aluminum or Carbon Fiber Mountain Bike Frame? By Christian Galvan ENGR M12 May 12, 2021

2 ABSTRACT In the following paper the advantages and disadvantages of aluminum and carbon fiber mountain bike frames will be compared, by comparing cost, overall makeup and durability, and how each frame performs while riding. It is important to compare aluminum and carbon fiber bike frames, because they are the most popular material for manufacturing mountain bike frames, and it is important to understand why a carbon fiber make is more expensive than aluminum frames. When comparing cost, overall makeup and durability, and the performance of these frames, carbon fiber proves that it is worth the extra money because of its overall strength and performance on the trail.

3 TABLE OF CONTENTS  Title page ……………………………..…1  Abstract………………………………..…2  Table of contents………………………..3  Introduction………………………………4  Costs……………...……………………4-5  Durability………………………..……..6-8  Performance………………………..…8-9  Conclusion…………………………… .... 9  References……………………….……10 INTRODUCTION

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4 Mountain biking is a sport that involves riding bicycles that are designed for riding over off-road terrain. The way that these are designed to handle these terrains and obstacles is done through the components involved on the bike, with the most crucial being the frame. There are four main materials that are used for constructing bicycle frames, these are aluminum, titanium, steel, and carbon fiber. Among many serious and amateur mountain bikers’, carbon fiber and aluminum frames are the most common. Since these are the most common it is important to compare them to each other to find out which material will provide the best safety and which would be best for a rider. In order to figure out which one would be the most beneficial for an average rider, it is important to compare costs, durability, and performance. COSTS For many experienced mountain bikers looking for a new bike, the price is often an afterthought because they prefer how the bike rides. However, for many new mountain bikers, they are looking for an entry level bike, and in this case, price becomes a bigger factor. When comparing aluminum and carbon fiber mountain bikes, the carbon fiber costs much more than the aluminum bikes. This is because of many factors, including manufacturing and the overall cost of the material. The main cause if the price difference is the manufacturing cost. There are many methods to creating a carbon bike frame, with the most common being using carbon fiber layers in a mold along with resin. The price for these molds range around $60,000 to $100,000 per mold.

5 The process of molding starts with laying the carbon fiber composite into the mold, and adding resin to hold and reinforce the fibers. This method allows for more ways of shaping the frame so it is more aerodynamic and stronger in more important places, which cannot be done with other materials. Using the method of molding also comes with some disadvantages, such as, if there is a wrinkle in the carbon fiber layers or resin build up. These problems would cause failures in the frame so a complete restart of the build would need to be done. Another disadvantage of a carbon bike frame is that carbon is not recyclable and ends up having a negative impact on the environment. The manufacturing process adds a hefty price to the end product for a consumer, with the average price a carbon fiber made mountain bike ranging from around $3,000 to $6,000. The other competitor material for most mountain bikers is aluminum, 6061 to be specific which is less expensive than other popular material used for mountain bike frames. The process of developing an aluminum frame involves a tempering process, which improves the alloys properties by performing a heat treatment. The cost of the aluminum itself and the ease of manufacturing an aluminum mountain bike frame allows for a high-end aluminum mountain bike to cost around $1,000 to $3,000 which is much less than a carbon bike.

6 Durability Most high-end mountain bikes are made to be very durable, so mountain bikers don’t really look into the mechanical properties of a particular frame when purchasing a new bike. Most mountain bikers prefer the to look into how the bike rides and how it feels beneath them on the trail. However, all these factors stem from how these frames are made. For example, many mountain bikers look for a stiffer bike frame for a smoother ride and to exert more power on the bike itself. Carbon fiber allows for a plethora of different characteristics on each frame because of the method used for creating the frame. The stiffness of a carbon bike frame can be calculated by, “[Carbon Fibers] are classified by the tensile modulus known as Young’s modulus, which quantifies the stiffness of an elastic material. Young’s modulus predicts how much a material bends or extends under tension or shortens under compression, the higher the Young’s modulus the stiffer the material. It is expressed as a ratio of stress over strain. The Young’s modulus E is given by where E is the Young’s modulus (modulus of elasticity), F is the force exerted on an object under tension, A is the actual cross-sectional area through which the force is applied, ΔL is the amount by which the length of the object changes and L is the original length of the object”, (Bowkett & Thanapalan). In result of creating a stiff frame, the frame itself will be strong enough to withstand the loads put on it from cycling. “To develop frames capable of efficiently transferring mechanical power, it is necessary to analyze frame response as a function of the force applied to the pedals during all

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7 pedaling conditions… A highly efficient frame has to deliver the mechanical power output of the rider to the drive train while minimizing energy loss due to the strain”, (Manolova 88). This does not mean that the frame will not break, in order to ensure that it will not break the toughness of a material is still needed. The toughness of a material tells how much energy needs to be absorbed before the frame fails. The tougher the material results in the more energy absorbed, meaning that the frame will bend much more before it fails. Carbon fiber is known in the mountain biking world, for having a high stiffness to weight ratio. The laying of the carbon fiber determines where in the frame there is stiffness and strength. When laying the fiber, if the forces placed on the frame are in the opposite direction of the carbon fiber layers, then the frame becomes very strong and resistant to force, but if the carbon fiber layers are not laid in a direction where they can’t go against a force it will cause the frame to flex. “Carbon composite structures are typically made up with a quantity of layers called plies, stacked on top of each other. Each ply needs to be bonded to the adjacent ply so it can transfer load If this bond is compromised the structural integrity is significantly reduced. It is common for the plies to direction to be of a differing angle from the plies immediately above or below as this gives increased strength”, (Bowkett & Thanapalan). There are particular areas where strength is needed, such as the headtube, and that is where stronger fibers are placed. However, the bottom bracket needs to be stiffer for more power to be exerted while pedaling. In this are stiffer fibers are used that are known as High Modulus. Carbon fiber is known for being a brittle material, which means where aluminum will bend before breaking, carbon fiber frames will fail suddenly if the area is taking focused damage.

8 Aluminum frames are built using hydroforming, which helps to form many shapes with the aluminum, specifically 6061. This starts with a blank tube, and high-pressure fluid forming the tube into the specific shape of the frame. Like the carbon fiber mold, this allows for different ride characteristics to be given to the frame. This is what makes the aluminum frame competitive with the carbon fiber, making it stiff and compliant, as well as lightweight. With both of these materials being resistant to corrosion there is very little that separates these two at the highest level. One of the things that does separate these two is that aluminum, over time, will fatigue much quicker than carbon. “There is no material in the table that has advantageous properties in each category, which explains why manufacturers continue to fabricate frames using several different materials”, (Rontenscu 679). Both aluminum and carbon fiber have their advantages and disadvantages, but carbon fibers advantages outweigh aluminums advantages. Performance One of the main factors in performance is known as “feel”. Many mountain bike riders look for a certain feel of bike that is unique to everybody. For many, it’s having a

9 lightweight bike that is easy to maneuver around with. Carbon fiber suits both feel and maneuverability. A carbon fiber frame dampens vibration, and its lightweight makes it very snappy and allows for power output to be quickly applied to the pedals and bars. This helps when accelerating and climbing, as it allows for less gravitational force to overcome as well as having less friction. Aluminum has long been known for having a very harsh ride. However, with the advancement in technology, it has allowed for there to be more stiff frames to be designed with aluminum materials. However, aluminum doesn’t allow much vibration dampen when compared to carbon fiber. The methods that are used for creating frames with these materials is where the difference between them lies. The process for creating a carbon fiber frame allows for a wider range of characteristics than the process of creating aluminum frames, making it much more preferrable. Conclusion There have been many materials used for making mountain bike frames over the years, and aluminum and carbon fiber have become the favorable materials. While both of these are among the lightest of materials, that create lightweight frames that will improve performance. Aluminum comes out on top when comparing price, but the price of carbon fiber bikes is slowly dropping. This makes the price for carbon bike frames worth it because of the ability to customize frame characteristics and its high stiffness to weight ratio. For most riders looking for a good lightweight bike the aluminum is most likely the choice for them. However, if they are looking for a lightweight frame with gains in performance, the extra cost of carbon fiber bikes is worth every penny.

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10 Works Cited  Rontenscu, C., et al. “Choosing the Optimum Material for Making a Bicycle Frame.” Metaluraija, vol. 54, no.4, Oct. 2015, pp. 679-682.  Groves, J. “Bicycle Weight and Commuting Time: Randomised Trail.” BMJ: British Medical Journal (online), vol. 341, 2010.  Manolova, Aneliys V., “Relationship between the Pedaling Biomechanics and Strain of Bicycle Frame during Submaximal Tests.” Sports, vol. 3, no. 2, 2015, pp. 87-102.  Bowkett, Mark, and Kary Thanapalan. “Comparative Analysis of Failure Detection Methods of Composites Materials’ Systems.” Systems Science & Control Engineering, vol.5, no. 1, 2017.