How a Globe of Death Works

The globe is typically made of bands of steel (hence the act's alternate name, Globe of Steel) that have been riveted together. Erwin Urias has been riding inside the Globe of Death for nearly four decades as part of the Urias Brothers act, and his family still uses a globe built by his great-grandfather, Jose Urias, in 1912. That's not their only globe, though. Like most acts, they have different globes for different settings and stunts. The one the Urias Brothers use most often is 16 feet (4.9 meters) in diameter and weighs 5,300 pounds (2,404 kilograms). They built it themselves as an improvement on their grandfather's original. "It's evolved into something more user-friendly for us," Urias said.

The globes are also stronger now than they used to be — and they have to be. When the motorcycles are whizzing around inside the globe at about 55 miles per hour (88.5 kilometers per hour), they're applying a force of 3.5 to 4.5 g's to the surface of the globe. "Steel does tend to snap," Urias said more calmly than a man with his job description probably should. But acts have taken that tendency, as well as different steel alloys, into account to create the globes they use today. Urias and his brother are certified welders and fabricators, so they've built it to suit their tricks and to keep them from flying into space.

Every act has its own take on the globe, though 16 feet (4.9 meters) is the most common size. In a smaller globe, you can ride slower and look faster, but the Dominguez Riders use a 17-foot (5.2-meter) globe, and Infernal Varanne promises to use the "biggest globe ever." Split globes can come apart in the center, creating a top and bottom half for riders to navigate. In 2006, the Garcia Family built a globe with a triple split — a top, a bottom, and a band in the middle that the riders circle.

No matter how you split it, or don't, the globe offers something that few other stunts do: the act is visible from all angles and heights. Once you roll that steel globe into place and shine some spotlights on it, everyone can see everything inside. It's really what makes the act so amazing — there's nothing hidden behind a curtain and no optical illusions. Just daredevils testing the laws of physics and the limits of bikes and bodies — which we'll take-on next.

Most acts use dirt bikes in their Globes of Death, often from a mass-market manufacturer like Honda or Suzuki. They can't be too heavy or to huge; a nimble motorcycle is going to fly around the sphere far better than a beast of a touring bike with panniers and full fairings. The bikes also don't need high horsepower, since they only go 40 to 65 miles per hour (64.4 to 104.6 kilometers per hour), depending on the act. But they're also not usually governed, so their engines aren't restricted to limit their speed. The riders can decide how much speed they need to hold fast to the steel as they spin.

Erwin Urias says that he and his fellow riders "always use customized bikes." He and his brother have actually become mechanics so that they can make the tweaks that will perfect the tricks. As Urias pointed out, "These bikes are not meant to go upside down or ride around on their sides." They customize the engine, suspension, chain drive and more. Their act uses 125-cc Yamahas, but they've bumped the engine's output up to the equivalent of a 150-cc bike. Higher torque also becomes important when you've got to go from a dead stop to flying around the inside of a globe without falling.

People often assume there are tracks inside the globe for the motorcycles to follow; or even more odd, some believe that there are magnets in the wheels to hold the bikes against the steel cage. But according to Urias — and physicists and mathematicians will agree with him — a smaller globe simply requires less speed to make the trick work. As a rider's velocity increases inside the globe, the centripetal force increases. That force is what's keeping the motorcycle's tires stuck to the walls of the sphere. Speaking of which, there's also friction (no magnets required) between the tires and the inner surface of the sphere to take into consideration. As the rider goes faster, the resulting friction begins to cancel out the force of gravity acting on the rider and motorcycle. The whole act depends on centripetal force and friction, and those factors rely on velocity. If the rider goes too slowly, the velocity won't increase enough to out-do the force of gravity, and the bike and rider will tumble to the bottom of the sphere. This is that potential "death" thing we were trying to stay away from.

The last piece of the Sphere of Fear puzzle is the rider — or, more accurately, the riders. One guy in a globe is not very exciting, but three or five or even eight guys is a show-stopper. Add someone standing at the bottom of the globe — or in the Urias Brothers' case, a woman hanging from the center of the globe by her neck — while a bunch of motorcycles whiz around and you've got an audience that holds its breath until the last motorcycle is safely at the bottom of the cage.

The surprisingly dangerous part isn't getting the motorcycles to stick to the inside of the globe. That's just physics, right? It's the g-forces and blood rush experienced by the riders. "When we go upside down," Urias said, "our heads are at grayout." For one of their tricks, Urias's wife, who is a professional aerialist, hangs from the center of the globe while three riders circle her. "When she crosses the midway point" as she's being lifted into place, "we can no longer see her, and she can't see us."

Luckily, or more likely by design, the Globe of Death act is only about 5 to 8 minutes long. And while there aren't tracks to follow inside the globe, there are patterns in the riders' heads that they follow. It's never precisely the same every time, but the pattern is precise in its execution. Timing is of course everything, which is why you'll see riders rocking back-and-forth in the bottom of the globe. The first few bikes take off, and then the rest rock for a few seconds, revving, watching and waiting for the exact moment they can begin their own loops.

Urias keeps physically fit in order to be able to take the beating that riding inside a globe delivers. "You have to eat right and maintain your weight," Urias said. "If you're heavy, the motorcycle takes the brunt of it." Urias also noted that taking care of the rider's body helps with protection in case of injury. He does basics like pull-ups and push-ups, and his son, who will soon join the act as a regular rider, runs for cardiovascular fitness. These are crucial elements when you're adding gs and removing some of your consciousness while performing.