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 Poland but it was opposed by cyclists' organisations. Bicycle helmet laws by country The wearing of bicycle helmets, and attitudes towards their use vary around the world. Compulsory use of helmets has often been proposed and is the subject of much dispute (see Bicycle helmet laws), based largely on considerations of overall public health. Only two countries (Australia and New Zealand) currently require and enforce universal use of helmets by cyclists. In some other jurisdictions, partial rules apply - for children, in certain states or sub-national areas, or under other limited conditions. Denmark and the Netherlands have a strong cycling