--- For folks in their 70's and 80's whose hips and knees start going out, those bikes keep them on the road. The motor is just for that little bit of extra help on the hills.
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"The bicycle is the perfect transducer to match man's metabolic energy to the impedance of locomotion. Equipped with this tool, man outstrips the efficiency of not only all machines but all other animals as well." Ivan Illich ('Energy and Equity')1974