Power Assist

Whether it's because of a minor disability, or just old age, not everyone can ride a bike. And in hilly or spread-out districts, all but the fittest people can feel daunted at the idea of relying on their own power to take them where they need to go.

The idea of putting a motor on a bike is almost as old as bikes themselves, but the idea of 'power-assist' has really come to the fore in just the last few years. Unlike mopeds, whose motors are their main means of propulsion, electric bikes are fitted with a small motor to help the rider when the going gets tough.The idea is not to make a faster, more powerful vehicle, but simply to flatten the hills and shorten the miles. The end product is essentially a fairly conventional bike, but one that lends a hand when required.

Electric bikes were pioneered during the 1980s, with various enthusiasts producing systems that were often based around a normal bike being retro-fitted with a motor. In 1990 the 'Velocity' was produced in Switzerland. This was a new development: instead of the motor connecting directly with the back wheel via a friction drive on the tyre or a separate chain and sprocket, its power was blended directly with that of the rider; the combined output was fed to the drivetrain. Since then, electronic 'couplers' have become common; they link the motor's output to the effort put in by the rider - so there's more assistance when you're working hard, for instance when climbing a hill.The motor only helps out when the rider is under pressure.

Consequently, some countries have enshrined couplers in legislation relating to power-assist bikes. If the transmission ensures that the machine behaves like a normal bicycle (albeit one with a rider whose legs get bigger on hills), then it is seen as such by the authorities. Other electric motors simply fit on to an existing bike and can be operated so that the power cuts in whenever the rider chooses.

Ten years ago, the electric-assisted bicycle was something of a novelty. But during the 1990s the idea really took off, and in the last few years sales have soared. Two-wheelers are less held back than electric cars by the difficulties in developing the next generation of rechargeable batteries. Less power is required, and it has been possible to produce machines that are of practical use. Consumer interest has also taken off - particularly in Japan, where sales have surged to over 150,000 electric bikes a year. The stage looks set for the rest of the world to follow suit.The electric bike will then come to be both a means of helping less energetic people back to mobility, and of drawing newcomers in to cycling. Fears have been raised that electric power will eclipse human power. But once healthy-bodied people get used to whizzing about on two wheels, they will probably come to learn that they can do the same under their own steam, without having to worry about charge levels. So their next bike might be a conventional mountain bike, and after that maybe even a city bike.