The guide of aerodynamic cycling

Cyclists love aerodynamic gear: aerodynamic bikes, aerodynamic frames, aerodynamic wheels, aerodynamic riding helmets, even aerodynamic smart watches! But do we really know how any of this works? Or what does "aerodynamics" really mean? Can these aerodynamic wheels maintain speed easily? Does aerodynamics matter when you're not riding very fast? Is your riding posture aerodynamic enough? Here is our guide to this article.

Definition of aerodynamics

Of all the obstacles you have to overcome on your ride, the two biggest are air resistance and (when the road slopes upward) gravity. You can avoid the latter by riding on flat ground, but unless you travel to the moon, you can't avoid air resistance. Even on a completely windless day, you create air resistance, and the faster you ride, the greater the air resistance. It is the main drag at speeds above 9 miles per hour (14.5 kilometers per hour). At speeds up to 30 miles (48 kilometers) per hour, 90 percent of your power is used to overcome what scientists call air resistance. While aerodynamics is the study of the properties of moving air and the interactions between air and solids, you, as a cycling enthusiast, should also understand how to reduce drag. Here's a quick review of the two main types of resistance you face: differential pressure resistance and surface friction resistance.

Pressure differential resistance

When you ride, you collide with air particles so violently that the air is compressed and then spaced apart as it passes over you; The pressure difference from the front to the back creates drag. Aerodynamic profiles are designed to reduce pressure drag by reducing pressure differentials, allowing air to flow more smoothly in front of you and reducing low-pressure wakes behind you.

Surface friction resistance

There's friction between your body and the moving air particles, and there's friction between the layers of air around you. The air above you is still; Air flows quickly and freely through the body. The transition between these areas creates friction, creating drag. Overall drag can be reduced by reducing surface friction, like the honeycomb concave you see on a golf ball or the textured material on the shoulder of a leather coat.

Cannondale Design Engineer Nathan, PhD, Applied Aerodynamics, Monash University, Australia. "Surface finish increases skin friction by making the air near the surface more turbulent," Barry says. The benefit of this is that the turbulent boundary layer has better energy transfer, which allows the flow to stay on the circular surface longer, thus reducing pressure drag."

There is a misconception that aerodynamics is only important when a driver is fast. "People say, 'I'm not fast enough to need aerodynamics,'" Barry explains. "Good aerodynamics also saves slower riders more time."

Indeed, the faster you go, the more air resistance drains your energy. Increasing your speed from 32 km/h to 64 km/h doesn't double the air resistance, it exponentially increases the air resistance by a factor of nearly eight. "At speeds approaching 48 kilometers per hour, 90 percent of the power is used to overcome air resistance." "Even at relatively slow speeds, most of your energy is going into overcoming air resistance," Barry says.

"At 16 kilometers an hour, half the power is against air resistance," Barry said. The slower you go, the more time the aerodynamics can save you because the more time you spend on the road overall. If you ride at 29 kilometers an hour, you can still save most of your time by reducing air resistance."

Reducing air resistance can even help you climb a hill faster. "On terrain with a gradient of about 6 percent, a bike with a pneumatic profile will be faster than a light bike, or the equivalent of a stronger elite level rider climbing 7 percent," Barry said. On this slope, you can save more energy for the same amount of weight.

When measured scientifically in terms of power, good aerodynamics can equate to easily maintaining speed and conserving body energy. Your aerodynamic equipment can greatly reduce air resistance, so you can ride farther and faster with less effort. Let's take a look at what's most important.

Your bike accounts for 30 percent of total drag, which is significant, especially for riders who don't use an aerodynamic riding stance on their bikes, says Dr. Len Brownlie, an aerodynamic motion research consultant at Simon Fraser University in British Columbia. "If you're not very flexible or if you're not built to ride aerodynamically for a long period of time, then a bike that reduces air drag can help you compensate for that," he said. "No matter what time you're riding, an aerodynamically designed bike will always reduce drag for you."

For the bicycle itself, even if the bicycle is very fast at the beginning, the tube aerodynamic optimization can still save a lot of time.

For example, when Cannondale engineers tested SystemSix, they found that using the same wheels as another regular road car could save SystemSix drivers two minutes over a 40K race. The SystemSix is the brand's first thoroughly aerodynamic road car, while the Evo is a race car.

If you compare an aerodynamic bike to a traditional low-frame wheel race car, the savings are closer to three minutes. "Getting the cockpit design right makes a big difference," Barry says. "At the very front of air resistance, optimising the traditional tubular handlebars to aerodynamic handlebars is very important to reduce drag."

What's more interesting is that disc brakes don't just increase the ability to slow or stop, Barry explains: it's a more aerodynamic frame structure. If you give up the traditional ring brake and use the disc brake, then there is a lot of freedom in the design. In terms of drag reduction, you'll see a lot of improvement."

Riding helmet

According to Brownlee's research, using a classic pneumatic TT helmet instead of a standard road bike helmet can save you more than a minute during a 40K race at speeds of 50km/h. But TT helmets are notorious for poor comfort and various restrictions on use. Fortunately, today's pneumatic helmets are better and more comfortable than ever before. "Modern pneumatic helmets, such as the Giro Vanquish and the Specialized S-Works Evade II, are very close to traditional full-coverage TT helmets in terms of aerodynamics, but they are more comfortable."

Riding equipment

In the 40K time trial, for example, a rider with the same amount of power finished more than two minutes ahead of a rider in a tight, state-of-the-art cycling suit than a rider in an ill-fitting club suit. Engineers are focusing on drag reduction in cycling clothing, says Brownlee, who has also worked with Nike on a spoiler design, which resembles a series of tiny wings.

Brownlee says that for sprinters in track and field, they can reduce resistance by 10 percent, which is equivalent to a 1 percent improvement in 100 meters. "There are a number of cycling apparel manufacturers that have developed similar time trial cycling suits, these textured fabrics that have a turbulent effect, and design them into the shoulder, upper arm to elbow, thigh and other windward face positions, which allow the rough air to flow over your limbs and hold it close to your body with less resistance."

However, Brownlee points out: "There is also a diminishing marginal effect to this drag reduction. Our recent wind tunnel testing of time trial riding suits shows that some space suit designs can be taken to extremes by having too much textured fabric; The lowest resistance suit we tested limited the textured fabric to the shoulders and upper arms and relied on a seam design aligned with the airflow for a very smooth and tight fabric. "In our tests, bike wear manufacturers Castelli, Sugoi and Bioracer provided the best drag reduction results."

Wheel set

"The wheels are complex, and the fact that they are paired with tires can dramatically change drag," Brownlee said. A few years ago, we ran the same aerodynamic front wheel test with tires made by five different tire manufacturers. We were surprised to find that wheel resistance varied by as much as 9% with different wheel sets. But in general, the 60 mm to 90 mm frame height of the rims will minimize air resistance. "

How does a rider achieve a pneumatic riding attitude?

When you want to reduce drag, first look in the mirror. You, the rider, are bigger than your bike, accounting for 70 to 80 percent of the overall windward resistance cross-section, Brownlee explains. There is no doubt that lowering your torso can significantly reduce the windward resistance surface and overall drag. The point of diminishing returns is reached faster than you think. Barry and a team of Monash University researchers conducted a study in which they simulated the speed of an elite road race and Ironman triathlon with a range of hand and body positions while riding at 45 km/h wind resistance.

The highest resistance position is the classic vertical riding position, which requires 430 watts to overcome air resistance as the rider shakes hands. Holding the lower grip saves a bit of energy, requiring 417 watts. Even more energy can be saved by bending your elbows and pressing down on your waist, which requires 385 watts. But the most effective aerodynamic position is actually a handshake, with the arms bent and the forearms parallel to the floor. In this position, the rider requires only 372 watts of power, a 13.4 percent power savings compared to the original hand position.

Bike Frames

The belief that carbon fiber bikes are more aerodynamic than aluminum bikes may come from carbon fiber's reputation for ease of handling. It can be made into any shape engineers can think of, opening up more aerodynamic possibilities.