A frame is the central part of a bicycle, onto which wheels and other components are fitted. The modern and most common frame design is based on the triple triangle design, a central front triangle, and a paired rear triangle. Frames must be strong, stiff, and light, which is accomplished by combining different materials and tube shapes. The length of the tubes and the angles at which they are attached define a frame's geometry. The geometry design is an essential consideration in the intended use of the bike. The frame is designed to surpass all ASTM and ISO bicycle testing standards.