In this blog post, we will look into the nature of drag that limits the speed of a bicycle and the possibilities of overcoming it.
What is the maximum speed a bicycle can reach? Can a bicycle that uses human leg power be faster than a car that uses an engine? To answer this question, we must first look at the different situations in which a bicycle can be faster. The current record for the fastest speed on a bicycle on flat ground is 132 km/h, set by a Canadian cyclist at the WHPSC 2008. This record was set on a velomobile, a type of bicycle that is a recumbent bicycle wrapped in streamlined material. At first glance, it looks like a thumb, with only the head protruding upward for visibility. The bicycle wheel protrudes only slightly, minimizing the air resistance the bicycle normally experiences when riding.
However, it is difficult to evaluate the performance of a bicycle based solely on its speed. A bicycle’s true performance depends on how efficiently it can run under various conditions and how harmoniously it moves with people and machines. These factors play a particularly important role in bicycle racing. This is because racing is not just a speed contest, but a comprehensive sport that requires strategy, endurance, and the ability to respond to situations. For example, in mountainous terrain with a high gradient, stability and control are much more important than speed.
So, how fast can a regular person go on a bicycle? If the same bicycle is used and the external factors are the same, the speed will depend on the leg strength of the rider. So, what if the same person rides the same bicycle? The answer is obviously the same. But what if the same person uses the same bike, but the wheels are just different? The results are staggering. If you’ve ever seen a racing bike, you’ve probably seen a wheel with no spokes. If you’re reading this, you’re probably wondering, “Why would anyone use a wheel with no spokes? Does the effect of the spokes really matter that much?” The reason has to do with drag force.
Drag is one of the aerodynamic elements and is one of the biggest external resistances a bicycle faces. For example, when you run 100 meters, it is because of the wind that you face that you have difficulty running forward. The drag force discussed in this article is closely related to air resistance. On a bicycle, the wheels are one of the important parts that move forward by using friction with the ground. When looking at a bicycle in motion from an aerodynamic perspective, you might think that the wheels would not have a significant impact because they occupy a very small area of the front. However, the wheels are the parts that move the most while riding, and they have a special impact on the surrounding flow, unlike when simply stopped. The numbers vary from bike to bike, but for a typical bike, the drag force is measured at around 35N when riding at a speed of 48km/h. This is about 10-20% of the drag force of a bike, which is the second highest percentage after a person.
The proportion of the human body can be sufficiently reduced through posture correction, but the part occupied by the wheel is only achieved by aerodynamic wheel design. So how can this be designed? G.S. Tew and A.T. Sayer (1997) published a paper on the influence of bicycle wheel design on the market. I conducted an experiment with wheels with six different spokes, and found something very interesting. In the case of a disc wheel (a flat wheel without spokes), the drag force is reduced by about 30% when the wind blows from the front compared to other wheels, but the drag force is greater when the wind blows from the side. This is because the characteristics of disc wheels do not allow the wind to pass through the sides and they receive the force as it is.
However, in the case of a bicycle running at 80 km/h, the influence of the wind on the sides is not so great, so disc wheels are used for racing bicycles. For example, when we run a 100-meter race, even if there is a lot of wind blowing from the side, we only feel the wind in front of us when we are running. Some readers may have questions here. Why do some racing bikes use wheels with spokes on the front wheel and only use disc wheels on the rear wheel? This is because the front wheel is responsible for changing direction. In the case of bicycle racing, where direction changes are frequent, the front wheel is a disc wheel, which increases drag due to the greater influence of side wind. To prevent this, the front wheel is designed with spokes.
Efforts are still being made to design aerodynamic wheels to reduce drag. I believe that wheels that generate minimal drag on the front and sides will be researched and developed one day. This research is not limited to bicycles. Reducing drag is an essential task for other means of transportation such as aircraft, automobiles, and yachts, and this will enable the development of faster and more efficient means of transportation.
As such, research on drag is not limited to bicycles, but is also affecting various mechanical devices used by humans. For example, it is important to minimize drag in the design of aircraft wings and car bodies. This not only allows you to travel further on less fuel, but also has a positive impact on the environment. Ultimately, research and technological advancements in drag are being made across all areas of human life. One day, we will overcome drag and enjoy eternal speed.
