The game here is that you want the bike to lean inward so much that it’s perpendicular to the track. The only way to do that without slipping down the slope is to be going very quickly, because then you’re like the swirling tea. The bike wants to continue in a straight horizontal line, but it can’t because the curved track is in the way. That pushback from the track is providing the inward force that keeps you going in a circle. The bike is pushing into the track so hard that when you add that push to gravity, it’s as if gravity has changed direction. Now you’re being pulled into the track, instead of downward to the center of the Earth. The faster you cycle, the more you change the direction of the effective gravity. It still feels as though you’re cycling on a wall, but at least it’s one that you’re glued to by something that feels familiar.
I understood the theory, but the practice was a bit different. For a start, there’s no resting. You can’t stop pedaling because you can’t freewheel. If the wheels are going around, your legs are going around and that’s just the way it is. On a few occasions, I instinctively paused as I would if I needed a couple of seconds’ rest on the road, and I was rewarded by a gigantic kick of adrenaline as the bike bucked me up out of the saddle. You can’t freewheel on these bikes at all. You have to keep going, however much your legs are burning. If you slow down, you slide down the bank. I felt some new respect for the athletes who do this on a regular basis. And then there are all the other people on the track to contend with. If you move up to overtake someone, you are taking a longer path, so you have to increase your speed a lot even to have a chance. I was quite happy not to do too much overtaking.
The lesson from all this was that if you’re doing things right, the steeper slopes will give you a stronger inward push. And the reason that you need that push on the ends but not along the sides is that the semicircular ends are where you’re changing direction. The more quickly you change direction, the bigger the push you need to make it happen. If you tried to cycle this quickly on a flat track of the same shape, you’d skid out to the sides—tire friction alone can’t supply that inward push. The velodrome is what happened when the cycling world refused to allow its need for indoor speed to be limited by friction.
If you’ve ever wanted to know what it feels like to be a penny rolling down a whirlpool-shaped charity donation funnel, this is the way to do it. At the end of an hour I was properly fired up on adrenaline, and really glad that it was time to stop.* The scary thing about the effective gravity pulling me into the track was the knowledge that if I slowed down suddenly, it would change back. And gravity pointing downward is a pretty uncomfortable thought when you’re cycling on a 43-degree wall.
The cyclist is being pushed inward by the track in the same way that the ground is pushing up on us all the time. If the ground underneath you suddenly vanished, you would fall because gravity is pulling you downward. So the ground itself is pushing back on us, to counter gravity’s downward tug. Cyclists feel the track both pushing them upward and pushing them inward. Overall, that will feel as though gravity is pulling them down and outward.
There’s a track cycling event appropriately called the “flying 200-meter time trial.” I reckon it must feel like flying, even though it’s called that because they’re already up to speed before the clock starts. The world record at the time of writing was set by Fran?ois Pervis and it’s 9.347 seconds. That’s 69 feet every second, or nearly 48 mph. For him to spin around the end of the track at that speed, the track has to be pushing him inward almost as hard as the floor is pushing him upward. Fran?ois was glued to the track by a force almost twice as strong as normal gravity.
As we saw in chapter 2, a constant background force like gravity is useful for all sorts of things, although some of them (like separating out cream) take ages. But spinning offers us an alternative. You don’t need to move to a new planet to reap the benefits of increased gravity. Cyclists can almost double their effective gravity at the top of a track, but even the best track cyclists in the world can “only” get up to about 50 mph. In theory, you could just keep spinning faster and the forces on you would keep getting stronger.
Remember gravity helping the droplets of cream to separate from the rest of the milk and rise to the top of the bottle in chapter 2? If the force pulling the milk downward is only as strong as gravity, it takes a few hours for the fat droplets to separate out. But if you put the milk in a long, spinning tube and whizz it around very quickly, the outward pull is so strong that the cream droplets will separate out in just a few seconds. This is how all our cream is separated from the milk these days—they don’t just let it sit and wait for it to sort itself out. Modern food production doesn’t have the time for that. Spinning something around generates a pull that can be as strong as you like, as long as you can spin fast enough. This is what a centrifuge is: a spinning arm that can hold on to something, pulling it inward to make it spin, and making the object feel as though it’s being squashed against the outer side by a very strong force.