Today, you hardly need 500 Euro and a few mouse clicks to buy a cheap kit with which you can convert a bicycle into a pedelec. Numerous web shops offer not only motors, batteries, cable sets and control units, but also wheel spoking with hub motor. Subsequently, provided technical understanding and experience in the field of bicycle assembly and maintenance, it’ll take you only a few hours of work until every component is neatly assembled on your bike. At the end of the day, converting the own bicycle into an e-bike seems to be a good bargain: For a new pedelec you finally have to pay 2,000 to 3,000 euro to your bicycle dealer.
But the comparison of prices already is flawed: Most of the retrofit systems are of poor quality and often of a very simple structure. It starts with the sensors: In most cases, only a motion sensor is clamped between crank bottom bracket and frame.
RETROFITTING – A LOAD PROBLEM
But the whole thing is not only a question of motor quality. The problematic thing with retrofitting a bicycle – and really dangerous – is the fact that an electric drive subjects a bicycle to higher loads than the cyclist could generate with his muscle power alone. In particular the easy-to-assembly front wheel hub motors generate an enormous stress on forks and frames. In addition, pedelecs are used at higher speeds, they are heavier and often packed with heavier luggage than bicycles without assistance. The user behaviour also changes: Casual cyclists turn into frequent cyclists and the motor power pushes them longer and steeper climbs uphill from where they have to come down in one piece afterwards.
All this means a greater load for pedelecs than for city and touring bicycles without motor; frames, components and brakes must be designed accordingly.
ANYONE WHO BUILDS BECOMES MANUFACTURER
An important fact to know: Whoever converts a bicycle into a pedelec, becomes the manufacturer of the entire system. If a part fails, the manufacturer of the original bicycle will not only reject any warranty claim; i.e. in case of a fall due to material failure, the original builder of the bicycle can reject the liability. And the owner, i.e. the one who performed the retrofitting, will hardly be able to prove that the bicycle was deficient or unsafe already without motor.
And whoever hopes that retrofitting could be done simply and with confidence by a dealer does not escape the dilemma. Legislation does not directly prohibit retrofitting to dealers, but in actual fact. Because: In the event, a dealer converts a bicycle into an e-bike, he becomes manufacturer (see above) and has to lead the entire pedelec through the conformity assessment procedure.
TUNING – FORBIDDEN SPEED
Converting into "E" is one thing, tuning a pedelec for higher speed, is something else. Granted. 25 kmh, i.e. the speed limit for normal pedelecs, is not really fast. That speed is achieved by many cyclists without motor on the flat. US Americans are in a better position in this respect. In the US the limit for identical pedelecs is 20 miles, i.e. 32 kmh. So, why shouldn’t you help a little discreetly in this point? In former days this was not unusual for motorcycles...
PREFERABLY ON THE SAFE SIDE
Do-it-yourself or tuning – both options seem simple, clever and low priced at first sight. But on the contrary: Both options bear considerable risks and are occasionally prosecutable. Everyone who wants a safe pedelec would be better advised to buy the model of a renowned manufacturer in the specialist trade. That costs a bit more, but in turn you obtain tested quality with service provided by a dealer, plus warranty and guarantee on top.
A component which holds on trekking bikes, but fails on pedelecs is a daily reality for experts. On the one hand pedelecs have to withstand higher loads and on the other hand the requirements applicable to a few safety relevant components or the frame were either considered a little in the past or not at all by the standards and therefore not tested. If several of these factors interact, frames or parts can break suddenly, all the more in the case of retrofitted or tuned pedelecs. As an expert I strictly advise against running the incalculable risk of retrofitting or tuning.
Graduate engineer Dirk Zedler, publicly appointed and sworn in expert for bicycles and electric bicycles
Author: Dirk Zedler