Ovalised chainrings have been used to great effect on time-trial bikes and even mountain bikes. Fabien Barel has even used one to gain EWS podium places.
The theory states that they even out the spikes in the rider’s power output, giving a higher gear when the pedals are level and a lower one at the dead-spot when the pedals are aligned vertically. This is claimed to give a more powerful pedalling action by maximising the time when the legs can give the most power to the pedals.
This 32-tooth example from B Labs alternates between the gearing of a 30t and a 34t ring. Therefore, compatibility may be an issue with some chainguides, but we were able to fit it around our Specialized top guide. For testing, we ditched the guide. The tall teeth and narrow-wide profile kept the chain on despite several rough rides.
Despite using a clutch derailleur, we could determine no increase in drivetrain-drag due to the rhythmic movement of the cage, which is necessary to accommodate the motion of the asymmetric ring.
On climbs, the odd sensation of the alternating gearing soon subsided, and the flattening-out of the power-spikes made maintaining traction easier. We can’t say whether it gives more power, but the advantages are clear when tackling steep climbs.
This article was originally published in What Mountain Bike magazine.