cylinder shape (parabolic) to help keep the rider in the center of the rollers. Frame The frame may be made from welded steel or extruded aluminum. The frame may fold in the middle for storage or transport. Variations Rollers are available in different widths (from 10" to 18") and diameters (from 4.5" to 2.25" for higher resistance). Some bicycle rollers use two front drums or cylinders instead of just one. Resistance may be added by having the spinning rollers driving some additional mechanism such as a fan. Some rollers have an internal flywheel on the back cylinder. This mimics real-world resistance to continuous acceleration and makes it possible to coast for up to 30 seconds. It is possible to remove the front wheel and mount the front fork in a stand (usually sold separately) to duplicate the stability of other bicycle trainers. Some rollers place the roller frame inside an external track so they can move (slide) fore and aft - which allow for simulating extreme pedalling off the saddle, as if climbing a hill. Strong elastic bands or springs are attached to each corner of the frame and pull and hold the roller frame in the tracks. A bicycle on the road can move fore and aft relative to the rider, and these rollers attempt to duplicate this effect. Roller racing Rollers may also be used for roller races (or goldsprints if fork stands are used). Two or more bikes are placed on rollers side by side, with the rollers connected to a timing system. Timing systems either use modern electronics and digital projection, or a large analog clock with a hand for every rider representing their distance traveled. Roller racing was popular in 1950s Britain, often preceding films at the cinema or taking place in between dances at dance halls. The British Schools Cycling Association carries on the tradition of true roller racing without fork stands and maintains the BSCA National Competition Roller Records In 1993, the Century Road Club Association of New York City retired their vintage rollers and mechanical dial for Kreitler Rollers and a computer system that could clock up to six racers at a time. Elsewhere in America, every winter a USA Cycling sanctioned event called the Iowa Roller Race Series defines roller racing champions. The series uses Kreitler Rollers and a DOS program Roller Fusion, which was commissioned in the 1990s by the