How drafting cuts air resistance for racers

HostYou know that feeling when you're riding a bike and a big gust of wind hits you right in the chest? It feels like you're trying to pedal through a giant bowl of thick soup. It's exhausting. But then, if a truck passes you or another rider pulls in front, suddenly everything feels easy for a second. Why does that happen?

GuestIt's because air is a lot heavier than we think. When we walk around, we don't really feel it, but as soon as you start moving fast, like on a bike or in a race car, the air starts to act like a wall. At high speeds, almost all the energy a racer uses is just spent trying to shove that wall of air out of the way. When you get behind someone else, they're doing that heavy lifting for you. They're punching a hole through that wall, and you're just sliding into the space they cleared.

HostSo it's basically just hiding from the wind?

GuestIn a way, yeah. But there's a lot more going on than just hiding. Think about a leaf in a fast stream of water. If the leaf is right behind a rock, it stays still or even drifts toward the rock. That's because the rock is pushing the water aside, and right behind the rock, there's a little pocket where the water is calm. In racing, we call that the draft or the slipstream. When you're in that pocket, the air isn't pushing against you anymore. In fact, because the person in front is moving so fast, they're actually leaving a bit of a low-pressure zone behind them. It's almost like a tiny bit of empty space that wants to pull you forward. You can go the same speed as the leader while using a lot less power.

HostThat sounds like the person in the back is just getting a free ride. If I'm the one in front, and someone is tucked right behind my back wheel, surely they're just stealing my hard work? It feels like they're just acting like a parasite.

GuestYou would think so, right? It feels like the person in front is doing all the work while the person behind is resting. But here is the wild part. The person in front actually goes faster when someone is right behind them, too.

HostHang on. How does that work? If I'm the one hitting the wind first, how does someone behind me make my life easier?

GuestIt has to do with how the air closes up behind you. When you move through the air, you don't just push it out of the way at the front. The air has to rush back in to fill the hole you left behind your back. Usually, that air comes rushing in and creates all these swirls and messy patterns. That messy air actually pulls on you. It creates a kind of suction that tries to drag you backward. But if another racer is right behind you, they basically plug that hole. Their body or their car takes up the space where those messy swirls would normally be. So the air flows smoothly off your back and over them. You both become one long, slippery shape instead of two separate, clunky ones.

HostSo you're saying if I'm leading, I actually want someone on my tail? That still feels like it flies in the face of how racing works. You want to be alone in the lead, not helping the guy behind you.

GuestWell, you want to win, sure. But if you want the whole group to go as fast as possible, you need to work together. In a bike race, you'll see a line of riders all tucked in, inches apart. They take turns at the front because the person in front still burns the most fuel. But the whole line moves much faster than a single rider could ever go on their own. They're sharing the work of moving the air.

HostOkay, but what about the big pass? Everyone talks about the slingshot move in car racing, where a driver zooms out from behind and somehow gains a massive burst of speed to overtake the leader. If the leader is also getting a boost, how does the person behind them manage to go even faster to get past?

GuestThat's all about timing and a little bit of a pressure trick. When you're in that pocket behind the lead car, you're saving up your engine power. Your car isn't working as hard to maintain the speed. Then, when you decide to pass, you pull out into the clean air. For a split second, you still have all that built-up momentum, but you're also not being held back by that suction from the leader's rear end anymore. You get this little pop of speed. It's like you were being towed on a rope and then someone cut the rope while you were already moving fast.

HostIt sounds incredibly dangerous. If you're inches away from a bumper or a tire at eighty miles an hour, one tiny mistake and everyone crashes. Is the boost really worth the risk of a massive pile-up?

GuestIt's a huge risk, and that's why it takes so much skill. If you're too far back, you lose the pocket and you hit that wall of air again. If you're too close, you touch. In bike racing, riders are often so close their tires are nearly touching. They have to trust each other completely. If the leader moves even a little bit without warning, the person behind has nowhere to go. But the physics are so powerful that you almost have no choice. If you don't draft, you'll get tired and fall behind while the rest of the pack sails away.

HostIt's funny because you even see this in nature. If you look at a flock of geese flying in that big V-shape, the birds in the back are basically doing exactly what race car drivers do.

GuestThose birds are experts at it. Each bird flies slightly above and behind the one in front to catch the lift from the air coming off their wings. When the lead bird gets tired, it cycles to the back of the line so it can rest in the easy air while another bird takes over the hard work of breaking the wind for the group.

HostThe next time I'm struggling on my bike against a headwind, I'll be looking for a bird or a bus to hide behind.

HostAir feels like nothing until you try to move through it fast, and then it becomes a heavy weight you have to carry.

GuestEvery racer knows that the air is a wall you can either fight alone or move through together.

HostBiking into a gale doesn't feel quite as lonely when you realize the wind is just waiting for a partner to help push it aside.