Electrically powered bicycles

Power assistance for bicycle has been around since the end of the Second World War, driven at the time by austerity.  The assistance was provided by a small petrol powered  two stroke motor either built integrally into the rear wheel, or bolted in some manner to the bike frame and driven by an auxiliary chain.  Some of these units can still be purchased today, but are now more a  novelty.

Improvements in electronics, and more particularly battery technology, has seen electrical assistance displace petrol engines as the principle motive power.  Today electricity powers the bulk of power assisted bicycles with most units being produced and used in China. 

 In the early 90’s Yamaha released a pedelec electric bicycle.  Although it sold well in Japan, it didn’t do well in Europe possibly because it was ahead of it’s time with petrol prices yet to bite hard, possibly because it was aimed at cyclists who couldn’t see the point, or if they could were not prepared to pay the price, and possibly because Yamaha failed to understand that there was a large potential market for the bike amongst non cyclists.  Yamaha withdrew from the European market, however they had sown the seed of the idea which has since grown so that 1 in every 8 bicycles sold in Europe is now sold with some form of electrical assistance.

 With electric assistance there are two options for power delivery, normal throttle as on a motorcycle, or pedelec, where power is delivered only when you pedal. Many power assist systems available offer the riders the choice so that they can pedal or not pedal as the mood takes them.  The principle advantage with pedelec is that by pedalling the rider can at least double and often triple the distance the bike will go on a single charge.

 Pedelec systems need a sensor to detect the rider peddling. The most basic pedelecs have a crank sensor that simply detects movement in order to activate the motor.  The more sophisticated have a torque sensor that detects not only movement but also effort and continually adjusts motor power in accordance to the riders effort.  The Canadian firm BionX manufacture a motor and controls that allow the rider to set the amount of assistance required.  So, for example, when struggling into a head wind the rider can select 100% assistance, but with a tailwind cut the assistance level back to 15% or less.

The less assistance, the further you go between charges.

 Electric motors are attached to bicycles in three ways.

  1. motor built into front wheel – cabling to the motor for power and control is run down the front fork legs and attaches via a plug to the motor( to allow easy front wheel removal in case of puncture).  This is by far the most simple method of installation, despite the length of cabling required.  With motors becoming more compact and lighter, it has minimal affect on the bicycles handling.  The existing gearing on the bicycle is not affected.
  2. motor built into rear wheel – the advantages of this arrangement is the short cable lengths between the batteries and the motor, and the pedelec torque sensor can be built directly into the motor.  The disadvantages are that all weight tends to be concentrated around the back wheel, and that only derailleur gearing can be used.
  3. crank motor – this is considered the most sophisticated and generally the most expensive.  Crank motors power the pedal cranks and therefore do not affect the choice of gearing which can be derailleur or hub gear.  The principle advantages of crank motors are electrical efficiency and centralisation of weight .  Most crank motors can only be used for pedelec assistance but the very sophisticated American manufactured Optibike, gives both options. (Check out their website). I believe there are also some retro fit crank motor kits around but they are complex to fit (not simply replacing a wheel) so that most crank motors come fitted as a complete package in a specifically designed frame. 

 If you intend to buy an one of these bikes or perhaps retrofit a motor to your existing bike there are a number of things to consider.

  1. Is your bike strong enough to carry the additional weight of motor and batteries ?
  2. In which wheel will the motor be installed? 
  3. What battery should I choose?
  4. Are the existing brakes on your bike up to the task of stopping the additional weight from the additional speed?
  5. How hard will it be to ride the bike without assistance?
  6. There are plenty of charlatans out there, so be careful in your selection of a supplier.  Make sure you are given a warranty especially for the batteries.

The growth in this market has encouraged some more familiar manufacturers to produce electrical assist kits.  Bosch has indicated that they plan to become a leading provider in this field with the first bikes fitted with their products, a crank motor, being released in 2001.  Shimano have also released details of their different approach.  They will be offering from December 2010 a front drive system that can be electronically coupled to their 8 speed hub gear with electronic shift buttons.  More information on both these systems is available on their respective website.

 Finally you should be aware that in Australia a power assisted bicycle can be throttle or pedelec controlled, must be restricted to 200 watts, but may only be used on roads with power assistance. Power assistance is not permitted on cycleways.  Of course it would be difficult to tell if you are using power assistance in pedelec mode until you comfortably ride past some sweating lycra clad roadie on your upright.

About Peter Bartlett