Bicycles with electric pedal assistance are trendy. According to the ZIV, the national representation of the interests of the German and international bicycle industry, the number of e-bikes sold increased from 1.95 million to two million from 2020 to 2021. Could a conversion kit be also an alternative? With such a kit a normal bicycle is converted into an e-bike. Uwe Wöll, Managing Director of the German specialized trade association VSF, and Dirk Zedler, publicly appointed expert for bicycles and e-bikes, explain whether this is a good idea or not.
Most retrofit kits consist of a motor, a battery and a control system. With these components and a little manual skill it is possible to convert a normal second-hand bicycle into an e-bike with electric assistance. E-bikes do not require registration, are considered bicycles in traffic and can also be used on cycle paths.
E-bike conversion kit: In most cases a hub motor drives either the front or the rear wheel
The drive units of such e-bikes must not exceed a continuous rated power of 250 watts and must switch off at a maximum speed of 25 kilometres per hour. According to Zedler, “the set usually includes a hub motor which drives either the front or the rear wheel”. But there are also mid-mounted motors for the bottom bracket. The advantage in this case: “With a motor that is centrally located in the frame, the weight distribution is balanced and front and rear wheels usual in the trade can easily be removed and remounted in the event of a flat tyre, for example", states expert Zedler.
A rear motor, however, located centrally in the rear wheel requires a derailleur gear and also makes the wheel removal and the mounting highly difficult. “Everyone should try out how it feels during the ride. But with a kit, a test is of course impossible”, the expert mentions.
Rechargeable battery for the conversion kit: The size depends on one’s own riding behaviour
There are considerable differences in durability as regards the battery. “Experience has shown that cheap batteries wear out much faster than those from brand battery suppliers”, says Zedler: “It may happen that the range will have halved after two or three years.” Everyone has to estimate on their own the size of the battery on the basis of their riding habits. For the five-kilometre daily commute to work, it doesn't have to be the biggest battery of all: “Therefore, most e-bikes have settled currently at 500 watt hours.”
What do the conversion kits for e-bikes cost?
The price range reaches from a few hundred euros to more than 1,700 euros for a retrofit kit. For those who do the sometimes time-consuming installation on their own no further costs will arise. Those who let the installation do by an expert pay at least 400 euros extra, according to Uwe Wöll of the German specialized trade association VSF. In addition, changes to components and bicycle adjustments may be necessary. Many offers are tempting, says expert Zedler: But those you want a high-quality drive system for retrofitting, almost have to pay the price of a complete e-bike.
What are the risks of converting your bike into an e-bike?
Dirk Zedler enumerates a number of risks. “The serious cycle industry strongly advises against a conversion,” says the graduate engineer. The motor and the rechargeable battery not only increase the bicycle weight, but also the average speed. This results in a higher stress on the material: “It has also turned out that retrofitting changes the usage behaviour.” Experience has shown that e-bike riders do not pedal as hard and therefore sit more upright in the saddle. This would increase the load on the saddle and the post leading to a higher risk of material failure and severe accidents. In addition, an e-bike drive would increase the stress on normal bicycle tyres: It is not for nothing that there are special electric bike tyres with higher load capacities and greater puncture resistance,” the expert comments.
Loads do not comply with the original usage behaviour
It’s especially a retrofitted motor for the front wheel that bears additional risks. The so-called torque arm is mounted to the fork and subjects the fork to loads for which it is not designed. And cheap batteries are also often the worse choice. Even fires could occur. And last but not least, there is the brake issue. A standard rim brake, for example, can wear out faster in e-bike operation. Zedler’s conclusion on retrofitted bicycles: “It’s playing with fire.”
Conclusion: A conversion is expensive, time-consuming and legally tricky in the event of damage
Anyone who wants to convert a bicycle nevertheless should definitely seek advice from an expert. Because laypersons are usually unable to assess whether their bicycle withstands the loads occurring when electrically driven. An expert opinion is, however, legally tricky for the professional. “The dealer is well advised not to provide it,” says Zedler. After all, he could be already held liable for the advice alone: “If anything goes wrong, the customer comes to the dealer.”
VSF Managing Director Wöll also sees a basic dilemma. In any case, retrofitting and adjustments of the bicycle are a matter for professionals. On the other hand, the bicycle dealer becomes the manufacturer in legal terms and must be liable in case of accidents. Strictly speaking, the dealer may only adapt bicycle parts such as frames, forks or brake pads to the requirements of an e-bike with the approval of the manufacturer in order to be released from liability; this effort is simply too great for both dealers and manufacturers.
If you spice up your bike with an e-bike conversion kit you will lose warranty claims
There are in fact two suppliers of retrofit systems that offer insurance covering liability claims, says Wöll. This is, however, about the insured loss following professional installation. With regard to the vehicle and the components, the specialist dealer remains liable and bears a risk. This means that the situation is difficult, even if the bicycle owner uses his own hands.
By the way: In addition to the safety risk, the German Cycling Association (ADFC) points out another problem: If you convert your bicycle into an e-bike on your own, you lose any warranty claims.
Author: Tobias Christ
Photo: © picture alliance/Uwe Anspach dpa-tmn