EBikes are not generally regarded as a glamorous area of cycling tech in the bicycling world, however if you travel outside of Australia, you’ll be surprised to see how quickly they have emerged as a major area of growth and innovation in the global bicycle industry. Unfortunately many bike shops hold a negative attitude towards eBikes and have tried their best to avoid them altogether. I know some shops will refuse to perform basic repairs on eBikes such as a fixing a puncture. For such reasons, the eBike industry has evolved outside of the mainstream bike industry in countries like Australia. To sell and service eBikes in regular bike shops, the industry needs to up-skill with better training. Like many mechanics, my own technical knowledge of eBikes is very limited, however as a wheel-building specialist, I’ve spent a lot of time working on eBike wheels and have become accustomed with the many issues affecting them. EBike wheels are unlike most bicycle wheels, and it’s these differences that have challenged me as a wheel builder. To build a strong eBike wheel, you need to be a wheel designer as much as a builder. Many eBike wheels utalise less than ideal components so you’ll often have to use every trick in the book to get the best outcome. As a supporter of all forms of cycling, I want to see growth in the eBike industry. However, I have reservations about the quality of some eBike wheels. Like many cheap mass produced items, many are simply not up to scratch. Wheel quality is important if riders are to have confidence in their machines.
Bicycle wheels are designed to perform a number of functions including carry loads, transmit power, and absorb shocks. However, the demands placed on eBike wheels are far greater than those seen on a regular bicycle wheels because eBikes carry heavier loads and subjected to far greater acceleration and braking forces. This means that an eBike wheels typically experience a much harder life than a regular bicycle wheels. The fact that many eBike riders tend to use their bikes for everyday transport over significant distances is a compounding factor. EBike wheels need to be built to a high quality if they are to last a long time. So what can be done to improve the quality of eBike wheels? Here are a couple of things to consider:
Focus on wheel design
Low and uneven spoke tension is the primary cause of spokes breaking on most wheels, particularly at the spoke elbow. Ebike hub motors need to be designed in a way that will balance spoke tension ratio between the drive and non-drive side hub flanges. One reason why front wheel eBike wheels are more robust is that the spoke tension ratio is more even, plus the weight load of the hub motor is more balanced at the front wheel. However, many riders prefer the feel of a rear-drive hub motor that are common on many eBikes. Both front and rear eBike wheels can be improved through a range of wheel design considerations including optimal flange spacing, spoke lacing patterns, and spoke/nipple alignment. However, because eBike hub motors often utalised in a range of different wheel sizes, the ideal hub design and lacing pattern in one rim may be impractical on another. As such it’s important that eBike manufacturers are savvy to science of wheel building to select products that are designed to fit within a particular range of wheel sizes. Even with crank drive eBikes, the load and transmission forces are still just as high as hub based motors, so wheel design and quality are just as important.
2. Improve component compatibility and availability
Some of the most common causes of wheel failure on eBikes come from incompatible components. I have seen hub motors with oversized spoke holes that are wide enough to fit motorcycle spokes (10-12g etc), yet the wheel was built with narrower 13g (2.3mm) spokes. There is very little one can do to attest spoke fatigue in such circumstances. Similarly, most bicycle rims are drilled with for 14g spokes (with 4.5mm spoke holes) will often have problems fitting a bulky 13g nipple. Thankfully Sapim have produced the 13g “reduction nipple” which alleviates this problem on many rims.
Likewise, single butted spokes like the 13/14g Sapim Strong are an excellent choice for fitting eBike hubs into regular rims with improved spoke durability from the cold forged butting process. Rim compatibility is also an issue when looking at the alignment of the spoke and nipple. Many eBike wheels have spokes that become kinked at the nipple because the angle that spoke travels to the rim at is too steep for the nipple adopt a good alignment.
This issue can cause premature spoke failure with spokes breaking at the thread. Rim manufacturers have largely reduced this problem by utalising directional drillings (both radial and axial) on eBike specific rims to optimise spoke/nipple alignment.
European rim manufacturers such as Ryde and Rodi are leading the way producing high quality eBike specific rims, however these products seldom make their way into small bicycling markets such as Australia.
3. Broaden the scope of eBike wheel building tools
EBikes wheels require a number of special tools to ensure that wheels are built and repaired to high standard. At the most basic level, it can be hard to find a good spoke wrench to fit 13g nipples. Well, it was a few years ago! I still see many shops using the old ‘ring style’ spoke wrenches that will easily round off nipples. I’ve found that the Park (Blue) SW3 is the best spoke wrenches available for most 13g nipples. A solid/firmly mounted wheel truing stand is a must for working on eBike wheels which have tendency to jump out of the stand. Tip: make sure the axle nuts and keyed washers are secured on the stand to prevent the wheel from falling out. Another problem with eBike wheel building is identifying spoke tension. Because many EBike wheels have a shorter distance between the spoke crossing and the rim, many tensiometers (e.g. DT Swiss, Park Tools, Wheel Fanatyk) will not fit to get tension reading. It might be unlikely that a tool manufacturer would consider creating a new tensiometer just to cater just for the eBike market, however without such a tool, it is difficult to build and repair many eBike wheels to the highest of standards.
4. Improve build quality
It goes without saying that build quality is a fundamental factor that affects the quality and durability of an eBike wheel. While many low quality machine built wheels may be “good enough” for regular bicycles that have minor use, a low quality eBike wheel will surely fail given the demands that are placed on it. EBike wheels that are hastily assembled with low quality components will suffer from premature spoke failure. To retain high spoke tensions, wheels need to be properly stress released with a corrected spoke path to the hub flange. In many cases, 2.3mm (13g) spoke head washers may be necessary to reduce any play at the hub flange. In my opinion, the best eBike wheels will always be made by hand because of the numerous processes required to achieve build quality can never be replicated by a wheel building robot.
Although eBike wheels are rarely associated with custom wheel building, there is a great opportunity for wheel building specialists to utalise their knowledge and provide support for this growing area of cycling. EBike conversions often require a wheel build because a certain wheel size rim may not be available in a prebuilt hub motor. Anyone for an electric fatbike? Specialist wheel builders are more likely to have the necessary tools to repair eBike wheels and produce the custom cut spokes required for the job. From my experience, most eBike customers are more than willing to pay for quality wheel building services because they value and rely on their eBikes for everyday transport. Unlike many bicycle wheels that are disposed of and/or upgraded every few years, eBike wheels are more likely to be rebuilt and repaired. Wheel builders have a great opportunity to embrace this growing industry, should we choose to go there.