Are round chainrings better? Not for some. And rather than accept the fact that the human anatomy has not given us the means to attain the most efficient power production throughout the pedal stroke-due to the unavoidable ‘dead spot’ with round rings-a few companies have looked to find a mechanical advantage, by moving to a more oval shape. Most notably, Shimano tried with their Biopace chainrings, which were introduced in the early 1980s. While Biopace ended up as a punch line-due to the orientation of the largest part of the gear coinciding with the weakest part of the pedal stroke- two European companies have forged ahead with non-round shapes. Both Rotor (from Spain) and Osymetric (from France) have emerged with their own designs, which have racked up ProTour wins to back up the science they tout.
Blacked out Osymetric rings on a team Sky bike.
The Osymetric chainring is the brainchild of French engineer Jean-Louis Talo. The radically shaped chainrings use a dual-cam design, with each cam lobe corresponding to the most powerful part of the pedal stroke, the down stroke. The design increases the gearinches of the chainring at the point where you’re able to apply the most force, but as you transition to your least powerful part of the stroke, or dead spot, the chainring reduces in size to speed you back into the power part of the stroke. For instance, an Osymetric 52-tooth chainring would be similar to a 55-tooth in the largest portion of the cam, then gradually reducing to a 49-tooth over the dead spot. Osymetric USA uses the same French design, but brings production to this side of the pond in Burlington, North Carolina. The aerospace machine facility makes the bare-bones, 2mm-thick, 7075 aluminum chainrings sans any type of shifting pins or ramps. The lack of any ‘chain-lifting’ ramps is in stark contrast to almost all other chainrings, especially in this price range.
The setup for Osymetric chainrings is not quite as simple as bolting them on the crank and riding away into the sunset. No, this is as much a task of mechanical skills as it is creativity. Once we mounted the chainrings (the easy part), we raised the front derailleur approximately 5mm higher than where it was traditionally adjusted for a 53-tooth round chainring. Fortunately, the front derailleur had adequate room for the necessary vertical adjustment, but on some bikes, that might not be the case, especially for those wanting to use a bigger chainring than a 52-tooth. Next, a spacer and screw (included with the chainrings) needed to be installed in the front derailleur cage to widen it slightly in order to reduce chain rub. About 40 minutes later, it was finally time to see if it would shift. After a couple of limit-screw and cable-tension adjustments, we got it to shift well. It wasn’t as smooth and crisp as our previous round-ring setup, but it was plenty rideable.
Our initial feeling on the first ride was the same as when you get on the bike after a huge ride the day before: your muscles are not firing correctly and your pedal stroke feels anything but smooth. By the second ride things were back to normal, so much so that we had to think about our stroke to realize it wasn’t going in a circle. When just cruising down the bike path, any benefits the Osymetric might provide weren’t felt, but once we upped the intensity, our pedal stroke seemed to become more fluid and powerful the harder we went. On climbs, one of the stronger testers felt it helped him maintain a slightly higher power at the same heart rate as a round chainring. Initially, we were worried that the 42-tooth inner ring would be way too much gear for the climbs, but it didn’t feel any harder than a 39-tooth round ring. Upshifting was not as quick as to what we were normally accustomed to, most likely due to the absence of any ramps or pins to help aid the chain in moving onto the large chainring, requiring us to back off the pedaling pressure to complete the shift.
We can’t exactly quantify the difference that Osymetric’s ‘mechanical assistance’ cam design provided us, but there was a noticeable advantage for a couple of the testers. No one disliked the chainrings, but it was the testers most in tune with their fitness who felt a distinct ability to maintain threshold-level climbing and time-trial efforts at a perceived lower intensity. Indeed, our issue with the Osymetric chainrings isn’t with the value they add to the pedal stroke; it’s the setup and fabrication necessary to reduce chain rub on the front derailleur cage and get the shifting dialed in. Once adjusted, we didn’t have much to complain about mechanically; although, we would recommend using a chain catcher, like the K-Edge, since the potential is there for a shifting mishap. While the Osymetric has a more extreme gear-ratio transition than the Rotor Q-Rings, it also is the reason they’re harder to set up. In comparison to the Q-Rings, the Osymetric’s extreme shaping theoretically provides the potential for a more powerful stroke, but at a cost of $35 more and lacking CNC-machined shift ramps. There’s already a handful of ProTour riders that are sold on the Osymetric chainrings, and they’re racking up results; however, it’s worth noting that the smallest 110 BCD (compact) Osymetric inner ring is a 38-tooth which, even with its varying diameter design, does not give it as low of a gear as the smallest (34T) round ring that can be used.
Price: $299 (pair)
Weight: 137 grams (pair)
Sizes: 56/44, 54/44, 52/42 (tested) in
130 BCD, and 52/38 and 50/38 in
For more info: Osymetric