One way to lighten a bike is to get rid of the chain. But if the cranks are attached to the axle of the wheel, then the wheel has to be very large in order to get any speed out of the bike. That is the design need that drove the velocipedes to have huge front wheels, and that design presented serious problems. Here is a design that does away with the chain, and has front wheel drive. However the crank is geared, and the power is transmitted via planetary gearing to the front wheel.