Most likely, the picture below shows a chainring you won’t find too often, or one might even think at first sight that he’s looking at a part which has either been damaged. But, things are far from being like this, as the part has been designed on purpose in this way, with one single goal: increasing pedaling efficiency.
You might say there is a lot of stuff a bicycle engineer could do to help people pedaling, rolling faster or stronger. It is and it isn’t so.
Several studies but also sportsmen hold that beyond weight and aerodynamics, it is crucial that the power with which cyclist’s legs push on the pedals it is transferred straight to the bicycle to produce mechanical work and thus higher rolling speed. And here’s where the oval chainrings come into action.
Even if this issue has not been too discussed, it is worth saying that even using clipless pedals together with cycling shoes, the force which the pedals are spinning is not constant during the 360 degrees of the rotation. This depends on the rider’s muscles, on how they are trained, but no matter how much training you might have, no one can avoid the dead spot. And you reach this dead spot each time when the cranks are perpendicular on the soil. To be more precise, if the crankset were placed in front of a clock, the cranckarms would be at 12 and 6 hours. These are the points where power generated by the pedals is very small, and here is where the oval chainring comes into action. It does not work wonders, but through its design it allows the legs to move the crankset easier, rendering pedaling more efficient.
The first crankset with oval chainrings was developed by Shimano in 1983 and it stayed in production until 1993. The Japanese patented it under the name “Biopace”. And it seems that the new chainrings were not a great success, a lot of people disputing their advantage of reducing the dead sport effect. This is why these chainrings were withdrawn from the standard crankset fitted on bicycles.
However, in recent years these chainrings have come back into the attention of cycling specialists, especially in road racing. Rotor and O.Syimetric started producing them, but with some changes from the initial design, as the chainrings are not only oval but some spots have been significantly flattened, resulting into an irregular shape, rather the oval one. The picture shows Bradley Wiggins, winner of Tour de France in 2012 and of the 2012 Summer Olympics Time Trial, who is using the O.Symetric Harmonic chainrings. Out of the scientifically proven benefices, their shape produces an increase in speed up to 3 km/h.
However, if these chainrings are so good, how come not everybody is using them? As we said, there is no bicycle to have them on the standard spec sheet, and buying such chainrings is no priority. Another aspect which discourages riders from using such rings is the alteration of gear shifting quality. Unfortunately, derailleures seem to be not so happy with these chainrings, even if Shimano didn’t receive any specific complaints.