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Riding With the Wind

7 minutes

(male narrator) Studies show wearing a bicycle helmet prevents 60% of head injury deaths. It also reduces the overall risk of head injuries by 85%. But wonder why cycling helmets are shaped the way they are? Or why serious cyclists don't look like this rider, wearing a loose-fitting T-shirt and long pants? Instead, many cyclists wear tight-fitting racing gear. Is it a fashion statement, or is it science? Specifically, motion dynamics. The reality is it's probably both. Riders might want to look good, but the laws of physics require a cyclist to overcome multiple forces to put a bike in motion, and aerodynamic clothing helps do that. You're always trying to balance the best aero position and the most efficient position for putting out power and trying to match the two to get the best combination.

(Salazar) Okay. Pedal for a minute, warm up, and we'll calibrate.

(narrator) David Salazar helps cyclists like Mike Byrd ride like the wind by riding the wind in the A2 Wind Tunnel in Mooresville. The most common misconception of wind tunnels is that air is blown over whatever object is tested. The reality is air is drawn through the tunnel because that way the air flow is more uniform. This is the back of the tunnel. There are three others. Air can be pulled through up to 85 miles an hour.

Fans are coming on. [alarm sounding]

What we do is, we want you to just do what you normally do racing, doing nothing special, and we're going to get some biomechanics measurements, as well as aerodynamic data.

(Graff) The A2 Wind Tunnel is the only one in the world that combines motion capture with high-speed cameras and aerodynamic sensors. That means that biomechanic and aerodynamic data can be captured in real time while the test is happening. So if a cyclist changes positions, or headgear, or alters anything during a test, the effects can be studied immediately.

(Byrd) How I can do better or get faster? Does an aero helmet or road helmet matter? It quantifies everything, makes it real. You can read magazines all day long, read about resistance, but seeing the numbers changing on there, it becomes very real.

(Graff) And here's why all those numbers matter. Cycling is good exercise because the rider must overcome a lot of forces to keep the bike from moving, so pedaling is work. Gravity pulls the bike and rider down. Drag from air resistance pushes from the front. There's vertical ground reaction is from friction between the tire and ground, and propulsive and rolling resistance from braking and inertia-- simply getting the bike moving. Make a turn while riding-- there's even more force working against the rider. Increase the friction on the wheel, plus torque and centrifugal force. The trouble is the laws of physics dictate that most of those forces can't be changed. Gravity is gravity-- nothing can be done. Different tires and bike designs reduce road friction, but only a little. Fortunately for cyclists, aerodynamic drag is the largest force a rider overcomes to get moving, and it's the one a rider can do something about. From 80% to 90% of the power put out is to overcome air resistance. If we can help them 5%, it's huge for them, especially over longer distances. They're already putting out so much power. Anytime you can help them, they finish the race quicker, or take less energy to get through the race.

(Graff) The first thing David notices is Mike pedals unevenly.

(Salazar) We're looking at the knee trace. Mike has had surgery on his right knee, which tracks differently than his left. This is more curved on the outside, this is up and down.

(Graff) Now look from the side. In separate tests, he wore a road helmet and sat in a more upright position. Then he tried an aerodynamic helmet in a tucked position. That lowered his torso by three degrees.

(Salazar) We're looking at his angles, but we compare this to his baseline position. This outline I took initially when we ran him, overlaid on this photo, you can see how much we've brought down not only his head, but his back-- the shape of his back has changed, and we brought him down quite a bit. It helped aerodynamically a lot.

(Graff) Mike ran 12 positions in one hour of testing. Looking at the baseline to the best, we're able to save him 13.3% drag savings. That equates to, at 28 miles an hour, it would take 382 watts to maintain that speed in the baseline position, whereas the new position with the aero helmet, it only takes 337 watts to maintain.

(Graff) A watt is a measure of power. Reducing drag means more efficient pedaling, so Mike uses fewer watts of power to go as fast. That saves him energy, useable in other parts of the race. So crunch the numbers-- that 44 watts of power saved, over a 10 mile race, would shave 57 seconds off of Mike's race time. Those same aerodynamic principles are used to design everything from bikes and helmets, as we saw at the beginning, to the cars that cyclists ride by, to the planes that fly above, all to save energy. That's big time, saving a lot of energy. If you're a triathlete especially, you'll run a lot faster and further, saving that 40 watts during the race.

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From cyclists to race cars, the motion of an object is determined by the sum of the forces acting on it. An aeronautics engineer works with Newton's three laws of motion to test the best bicycle posture and helmet in a wind tunnel.

Media Details

Runtime: 7 minutes

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