Single-speed bicycle on the situation, a messenger may prefer a mountain bike based single-speed, which can roll over many obstacles, or a fast and light road bike-based single-speed. In the United States market, bicycle companies such as Bianchi, Cannondale, Fuji Bike, KHS, Kona, Raleigh, Giant, Specialized, Swobo, Felt, Trek and Niner all have produced and marketed single speed bicycles. Because most full suspension frame designs either have a single pivot that is not concentric with the bottom bracket, or a linkage with a variable center of rotation, the distance between the bottom bracket and rear axle varies throughout the suspension's travel. This
Bicycle helmet laws by country helmet use. Australia was the first country to enact mandatory bicycle helmet use for all cyclists. Mexico City has had mandatory cycle helmet laws repealed, and in Italy the Federazione Italiana Amici della Bicicletta managed to block a proposed helmet law. While bicycle helmets are not required to be worn by law in the United Kingdom the British Medical Association advocates the compulsory use of helmets. Cycling UK, the largest cycling advocacy organisation in the UK, consider helmet wearing as personal choice rather than being mandated by legislation. In 2002 an attempt was made to introduce bicycle helmet legislation in