For a few years now, we have seen our wishes come true: More and more people switch over to electric bicycles. Many of them also ride many more miles than they did with their city or trekking bike. Baggage or trailer loads are no longer a deterrent, and neither are hilly terrain and strong headwinds. What’s more, on the strength of their e-bike’s motor and the longevity of modern batteries, riders who do not exactly boast the physique of a pro cyclist venture more and more into mountainous regions.
A frequent outcome: unexplainable punctures, frequent spoke failures or rims breaking in two along their well. What are the reasons behind these phenomena, which hitherto used to be encountered mostly by dealers with a lot of road cyclists among their clientele, even still in the era of the early system wheels? It is mainly on the manufacturers to improve the situation. After all, they are the ones who can get so many things right or wrong when building wheels. But if something does go wrong, it is up to the dealers with their workshops to help the customer out.
Testing is too lax
Modern e-bikes weigh approx. 10 kilograms more than city or trekking bikes made for similar types of use. But it is not just the bikes themselves that have gained weight over the past 10 years. The average man in the D-A-CH region weighed 89 kilograms, the average woman 71 – and that was before Corona hit. Would you have guessed it? Surveys have revealed that people gained an additional two to four kilograms during the pandemic.
The optional test on the roller test bench included in the applicable EN standard places a load of 640 newtons on wheels and tyres. Is that a lot? No, not even close! Assuming a typical wheel load distribution of 70 % of the weight resting on the rear wheel, a 30 kg heavy pedelec with a rider of average weight (90 kg) results in a wheel load of 824 newtons, which is almost 30 % more than what the test specifies. If the rider weighs 100 kg and carries with them 10 kg of baggage, almost 960 newtons would apply. The 750,000 impacts with 10 mm bumper height are not even worth discussing as they are simply not sufficiently demanding for a typical tyre with 40 to 50 mm width.
This means that testing according to the standard is absolutely inadequate for finding wheels with sufficient engineering strength for typical pedelec use. It is up to manufacturers and their testers to act.
Spoke count too low, spokes too weak
For many years rear wheels used to come with 36 spokes by default. This was pared down to 32 as the spokes got stronger over time. But for heavy pedelecs, subjected to high driving forces in combination with disc brakes, we should actually turn back time. Although, merely returning to the traditional spoke count will not suffice. The significantly higher loads will also require borrowing a few tricks from builders specialising in sport wheels. Double butted spokes are solid at the thread and bend but thinned out along their centre section. This makes for some elasticity in this section, relieving the two weak spots and drastically prolonging the lifespan. If a customer experiences repeated failure of individual spokes, it can be worthwhile to spoke the complete wheel with such spokes.
Flanges that are too thin
Read the entire article here