Gravity Sport can be defined as racing on an inclined track using wheeled craft powered only by gravity. Additionally, Gravity Sport vehicles have no mechanical brakes and they roll exclusively on urethane wheels.
I specify urethane wheels as the true nature of the gravity sports have those in common, separating them from other gravity powered sports like Soapbox Derby, Gravity Bike (a cycle sport often raced at Gravity Sport events) and Dirt Surfer. The unique properties of the urethane wheel group these sports effectively for racing on the same track. The true origin of Gravity Sporting starts with the Skateboard and the development of the Urethane Wheel.
Skateboards were around for quite a while before they were even ridable. The first skateboards were made from the very popular rollerskate with wheels that were originally made of steel. Essentially, these roller skates were nailed to boards and the first skateboard was born. With a ride that was more torture than entertainment, skateboarding still became popular. By the 1950s, this steel wheeled modification was manufactured into the first commercially available skateboard.
The clay skate wheels (aka, stone...) featured on the next "wave" of skateboards provided a bit smoother ride but it was still better at loosening fillings than anything else. And yet this "stone age" skateboard was shredded and torqued into movement that captured the essence of surfing on street. At this point, during the 1960s, skateboarding was featured in magazines, competitions were common and every toy store carried them. But soon the "sidewalk surfing" fad started to fade as more bones were broken and road rash was treated.
With the introduction of urethane wheels, skateboarding morphed from fad to sport. Now skateboards ran smooth and true. The urethane gripped pools, pavement and ramps like rare earth magnets. The unique rebound properties of urethane combined with its incredible durability provided a ride that was more like surfing than ever before. Additionally, manufacturers were able to easily "pour" new wheel shapes and create different durometer (hardness) wheels. This led to a wide variety of urethane wheels for different styles of riding. Skateboarders were now able to pull off bigger, more incredible tricks than ever as well as reaching much higher speeds.
The wheel bearing upgrade was the next important step in the evolution of the urethane skateboard wheel and Gravity Sports. The new sealed precision bearings meant no more loose balls hitting the dirt as well as the ability to swap out bearings with ease. Sealed bearings rolled smoother and remained clean longer. These new bearings were also much FASTER.
Nearly 40 years later and the urethane skateboard wheel remains the choice for Gravity Sporting. Not much has changed for the urethane wheel since then, however, there are more choices and a wider range of specs available for every type of Gravity Sport. Not just for skateboards, you'll find urethane on inline skates, street boards, scooters, "ripsticks", skateluges and countless industrial applications requiring casters or rollers. Urethane is even the material used for the bushings found on most skateboard trucks. Yeah, other materials have been made into skate wheels (Xtreme Wheels worked with rubber for years...) but nothing quite matches the magical properties of urethane. Urethane has proven to be the ONLY wheel material suitable for Gravity Sports.