A gravity racer is a motorless vehicle capable of holding a driver (usually a child) built for the purpose of racing or recreation. They are propelled by gravity and can achieve speeds upwards of 112 km/h (70 miles per hour). Originally, gravity racer cars were built from wooden soap (or apple) crates and rollerskate wheels, but have grown more sophisticated over time, with materials like aluminium, fiberglass and even CFRP being used. In the United Kingdom a Gravity racer car has been called a buggy, trolley, cart. It is currently popularly called a go-cart, although that now more often refers to a similar vehicle with a motor, spelt "go kart". In Scotland and northern England it has also been called a bogie, cartie/cairtie, guider or piler. In Wales it is often referred to as a gambo. In Australia they are called billy-carts. In addition to being built by children, there are organised competitions and races ("soapbox or billycart derby") that often engage the enthusiasm of adults. However, these things are usually entered into in a spirit of fun rather than serious competition. Often they will be fund-raisers for charity. Many, but not all, events impose the following rules: The car must have no motor The car must have at least 4 wheels The car may have to have some type of brakes The driver must wear a helmet A push at the top is allowed for extra speed Soapbox cars weigh an average of 150 pounds (68 kg) Many cities have permanent tracks where drivers compete for prizes. Please ZoooM to Zoooooooom down the road. Have a nice day.