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A gravity racer or soapbox is a motorless vehicle which is raced on a downhill road either against the clock or against another competitor. Although most are built for the purpose of recreation, some gravity racing teams take the sport more seriously and compete to win. They are propelled by gravity and can achieve speeds upwards of 112 km/h (70 miles per hour).〔(【引用サイトリンク】title=Speed Gun Data - Cairngorm Soapbox Extreme - The UK's longest and fastest gravity race )〕 ==Soapbox cars== 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 soapbox. 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 speed Soapbox cars weigh an average of and reach top speeds of . Many cities have permanent tracks where drivers compete for prizes. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gravity racer」の詳細全文を読む スポンサード リンク
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