All about bicycles, electric-assisted bikes, technology and safety in the press

Pedelec physics. Unfortunately, they have a lot going against them, too. No other frame design has seen more recalls than low step-through frames - with or without electric motors. Most of these are made of supposedly reliable aluminum. There have been many cases of frames breaking, resulting in falls that have sometimes very severe consequences. Products recalled by reputable companies are only the tip of the iceberg. As bicycle experts, we know of many other problematic frames whose problems are being ignored. Why are these rider-friendly frames at such high risk of breakage, especially when used as a pedelec? According to research and from personal experience, riding a pedelec increases a cyclists’ average speed by 5 kmh (3 mph). That doesn’t sound like much, does it? However, this means a typical 250-watt pedelec is constantly travelling with 75 percent more kinetic energy than a conventional bike. Impacts and bumps therefore affect pedelecs more severely than regular city bikes.

Other factors contribute to the problem: 

• Pedelec riders tackle terrain that is more challenging than they are used to. In other words, pedelecs let cyclists climb mountains that were previously insurmountable to them. The problem isn't going uphill; it’s that they eventually have to come back down as well.
• Pedelec users do not sit athletically in the saddle, but crash into every bump and rumble over every curb.
• Pedelecs are heavier and therefore under more strain. The electric assist encourages cyclists to carry heavier loads.
• Low step-through frames are not redundant. In other words, if one tube fails, there isn't any other tube to hold the bicycle together. The rider falls head first onto the road.
• Pedelec users ride more often, according to research by several manufacturers.

Taken together, this demonstrates that the potential for damaging a pedelec is significantly higher than for a conventional city or trekking bike. The e-bike components add to the problem. With the weight of a motor and a rechargeable battery, typical pedelecs with low step-through frames mutate into genuine wobblers. Inexperienced, less athletic cyclists – the typical clientele for these kinds of bikes – fall more because they often cannot cope with the pedelec’s handling. A wobbly pedelec doesn’t necessarily unseat its rider like a balky horse. Instead, riders alarmed at their bike’s shaking may brake too hard in panic, or ride the brake as they creep down a hill. That can cause the brake to fail, leaving the pedelec totally out of control, and there we go!

Stepping up to the challenge. The good news: It is entirely possible to design stable and durable pedelecs with low step-through frames. To do so, the designer, product manager and testing institute have to treat the pedelec as something other than a conventional trekking or city bike that just happens to have a motor attached. It does take some effort, but with the help of CAD systems and testing laboratories, safe pedelecs with low step-through frames are possible. There isn’t a simple recipe, such as adding an additional gusset or a welded-in cross tube. It requires the sum of many improvements, such as an adapted frame geometry, optimized tube dimensions, sophisticated welding procedures with thermal finishing treatments, a solid mounting of the bicycle rack, and functional cable routing. lt is possible to improve the riding characteristics of these kinds of pedelecs so customers can feel safe without shimmying. The safer these riders are, the fewer accidents they will have. In addition, the durability of a low step-through pedelec can become comparable to that of a mountain bike that is made to endure hard use. Only then will these kinds of pedelecs be able to cope with the increased strain of a heavy motor, heavy loads and heavy cyclists on a permanent basis.

Author: Dirk Zedler

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