A gravity bike is a specialized bicycle that has no pedals or chains and relies strictly on gravity for movement. A gravity bike can only travel downhill, relying on steep gradients and gravity to propel the bike at fast speeds, sometimes reaching over 90 miles per hour.
Traditionally, gravity bike riders start off with traditional BMX bicycles modified by lowering the handle bars and removing the pedals and chains. The seat is typically replaced with a banana or long serfa seat, letting riders sit further back. Weight is often added to the bottom of the bike to produce faster speeds and give riders a knee rest.