“I would like to query the basis of the electric bike range statistics you quote. I realise that you are ‘A to B’, but for many people, their use of such a bike for leisure purposes would be ‘A to A’; that is to say starting and finishing at the same location. If one assumes a hilly terrain, and ignores any flat areas, at the completion of a journey the uphill sections will have equalled the downhill. If therefore, one only used the electric-assist on the uphill sections, and turned the motor off on the downhill sections to freewheel, would the ranges you quote notionally be doubled?”
Michael Bartlett, Shoreham-by-Sea
Unfortunately, life is rarely that simple. For one thing, where a bike has the capability, the A to B testers usually opt for speed over range, which is why tests always quote the average speed.To keep speed up, the motor is often used for long periods on the flat, as well as climbing hills. Secondly, you never get back all the energy expended climbing a hill going down the other side! This is partly because motors tend to be inefficient when climbing at low speed, but primarily because most of the energy is dissipated in fighting the wind.This effect is barely noticeable at low speed, but descending a hill at 30mph will scrub off much of the kinetic energy stored on the climb…This is why ‘regenerative’ braking (recharging a battery or other storage device on a descent) is hardly worthwhile on a bicycle.
Think of the hill as a battery:Whether you ride a conventional or power-assisted bicycle, you store kinetic energy on the way up, and discharge it on the way down. A heavy freight train crossing the Swiss Alps will store a great deal of energy, which can usefully be returned to the electricity grid going down the other side, but a bicycle stores a tiny amount, and on such a small lightweight vehicle, wind resistance has a comparatively large effect. On a switchback road, the stored energy may enable you to get half way up the other side, so it can be useful, but in most cases, mechanical or electrical storage devices would be of little help. Now, where were we?
The A to B 17.6 mile test route starts and finishes at about the same elevation, but climbs and falls almost continuously in between, so the motor tends to be used for a high proportion of the ride.The figures published in the magazine are always lower than the maximum achievable, although they seem to equate fairly well to the sort of range a typical rider might expect, making shorter trips in heavier stop-start traffic.
In terms of maximum range, in level country, you might expect to exceed the A to B figures by 40% or more, even when using the motor much of the time. For example, the Powabyke or Ezee Forza can manage 50 miles relatively easily on the flat.
Most bikes complete the test course in 75-80 minutes, but the Forza did the run in 62 minutes – exactly 17mph. How can a bicycle limited to 15mph maintain such a high speed? The reason is that the more powerful machines cruise at close to 15mph and rarely fall below 10mph on hills.Add a few downhill bursts, and the average speed can exceed the maximum assisted speed…This is why electric bikes work so well in hilly areas.
