"Car" is the magic word for most teenagers today.   The simple word conjures up images of independence, romance and status that spill over into adulthood for many.   Perhaps more than any other people, Americans have had a special relationship with the automobile ever since Henry Ford put the vehicle in reach of the average person.   It may be difficult to believe, but a much simpler mode of transportation once had a similar attraction.   In the 19th and early 20th centuries, it was the bicycle that made Americans mobile. For the first time, the average person who could not afford to buy and maintain a horse and rig could travel increased distances in speed and comfort by his own power. Tandem models, which carried two to 10 people, allowed companions to share in the pedaling.   Boundaries were extended to the distance a person's energy could carry him. The bicycle was reasonably priced and easily maintained, requiring no feeding, stabling or cleaning up after.   The first U.S. bicycle craze, circa 1860-70, succumbed to faulty equipment and poor roads. Interest resurfaced in the 1880s with such improvements as the pneumatic tire.   In the 1890s, while farm prices fell and unemployment rose, the bicycle industry was thriving. Mass production methods developed by the bicycle firms, which typically employed about 50 people each, became a model for the auto industry.   By the turn of the century, the bicycle was a fixture with the public and the preferred mount of both police and the military.   The bicycle was a major influence in the life of my maternal grandfather, George Lester Sears, and thinking of it brings back fond memories of him.   It was his first major acquisition and his fascination with both its use and repair soon made him the acknowledged expert among his peers and earned him the nickname "Bicey." It also gave him one of the several trades he was to practice throughout his life.   The bicycle suited his restless and independent nature and he never outgrew his love for the vehicle. He never learned to drive or owned a car.   Though he was a blacksmith, farmed and worked in the silk mills, he was best known as a bicycle repairman.   Growing up, it seemed to me he divided his time about equally between the bike shop, the garden and fishing. I'd like to say he met grandmother bicycling. Actually, he skated across the frozen Susquehanna River one winter to court her.   Even marriage failed to constrain his urge for mobility. By my mother's tally, they lived in more than 20 locations in several counties and each of their nine children was born in a different place.   Perhaps his restlessness can be traced to his British ancestors who were seafaring men. Even after his forebears turned inland they kept their feet wet as canal boatmen, a profession that was in its decline as he reached manhood. Late in life, he confided he might have gone to sea had he not married.   A quiet man full with his own thoughts, he never put it into words. But, the bicycle may have given him some sense of the wind in his face that his genes craved and his erratic pursuit of new horizons may have had a similar source.   "Bicey" would doubtless be pleased that health and environmental concerns and sporting enthusiasts are contributing to a new surge of interest in bicycling.