to hold the tire bead securely, even if pressure were low or lost. In the late 1960s, the Varsity and Continental pioneered the use of auxiliary brake levers, which allowed the rider to rest hands on the straight, horizontal center section of the ram's horn handlebars, yet still have braking control. To further improve control from this more-erect riding position, the levers used to move the derailleurs (shifting the chain from one sprocket to the next) were moved from the traditional position on the "down tube" to the top of the headset, on a ring which would turn with the handlebar stem. This feature, attractive to older riders, soon found its way to other Schwinn models, especially those intended for senior citizens. By the mid-1970s, competition from lightweight and feature-rich imported bikes was making strong inroads in the budget-priced and beginners' market. While Schwinn's popular lines were far more durable than the budget bikes, they were also far heavier and more expensive, and parents were realizing that most of the budget bikes would outlast most kids' interest in bicycling. Although the Varsity and Continental series would still be produced in large numbers into the 1980s, even Schwinn recognized the growing market in young adults and environmentally-oriented purchasers, devoting the bulk of their marketing to lighter models intended to pull sales back from the imports. The bicycle boom The Sting-Ray sales boom of the 1960s accelerated in 1970, with United States bicycle sales doubling over a period of two years. However, there were clear warning signs on the horizon. Despite a huge increase in popularity of lightweight European sport or road racing bicycles in the United States, Schwinn adhered to its existing strategy in the lightweight adult road bike market. For those unable to afford the Paramount, this meant a Schwinn 'sports' bike with a heavy steel electro-forged frame along with steel components such as wheels, stems, cranks, and handlebars from the company's established United States suppliers. Though weighing slightly less, the mid-priced Schwinn Superior or Sports Tourer was almost indistinguishable from Schwinn's other heavy, mass-produced models, such as the Varsity and Continental. While competitive in the 1960s, by 1972 these bicycles were much heavier and less responsive in comparison to the new sport and racing bicycles arriving from England, France, Italy, and increasingly, Japan. Another problem was Schwinn's failure to design and market its bicycles to specific, identifiable buyers, especially