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Toolbox: Rotor Chainrings and Power Output
Over the past decade, non-round chainrings have made big inroads in the pro peloton and in the mass cycling market, led by Rotor and O-symetric. Given the complex muscular coordination required by pedaling, the theory of non-round chainrings of facilitating a smoother pedaling stroke can make sense, but what does scientific testing tell us about their performance?

The phrase “like riding a bike” is often used in North America to denote an activity so easy that anybody can learn to do it and will never forget it. On the face of it, the act of riding a bike is indeed a very simple thing and very hard to do “wrong.” Most riders indeed think nothing more of pedaling than setting their saddle height and then jumping on.

But the inherently unnatural act of pedaling (compared to walking or running) as smoothly and efficiently as possible requires a hugely complex coordination of multiple joints and muscles. When you consider that the action of pushing the pedals is repeated many thousand revolutions on each ride, it becomes obvious that even simple and apparently miniscule improvements in form or technique can result in major performance gains and also minimize the risk of injury.

Improving pedaling dynamics can be accomplished in a number of ways. The first obvious method is to improve the pattern of muscle recruitment during the complex task that is pedaling. The peak force generation comes during the downstroke, from about 1 to 5 o’clock positions. From there, much of the remaining pedal stroke is a “dead zone” where the leg is generating either minimal or sometimes even negative force (i.e. the other leg is actually pushing against the weight of the leg) during the upstroke from about 8 to 10 o’clock positions.

Much of the old advice (“scrape mud off your shoes to pull back during the bottom part of the pedal stroke) and the new equipment developed recently revolve around minimizing/eliminating the dead spots or otherwise smoothing out the power generation over the pedal stroke.

Big Bad Biopace
The first big wave of non-round chainrings was the Biopace from Shimano in the late 1980s. Intended to smooth out power transfer throughout the pedal stroke, they generated instead a strong love or hate (predominantly hate) reaction amongst cyclists. One reason for the hatred may be the marketing, in that Shimano: 1) forced it onto consumers with no option for a round chainring, and 2) introduced it only at the Ultegra level and below, but never at the “pro” level of Dura-Ace. As far as I can tell, minimal peer-reviewed scientific testing has been published on Biopace and its efficacy.

Rotor and the Next Generation
The past decade, non-round chainrings have been re-introduced into the cycling market. The first rider of note to adopt them was Bobby Julich using O-symetric in 2003. Now these have become popularized by Team Sky riders like Bradley Wiggins. For Rotor, their sponsorship of multi-World Champ Marianne Vos has been huge, with her winning rainbow jerseys in Road, Track, and Cyclocross with Rotor rings. And of course, the biggest marketing paydirt of all was Rotor being unbranded but ridden by Carlos Sastre in winning the Tour de France in 2008.

It must be said that, though hampered by the ghost of Biopace past, the “top-end” focus on pro cyclists using non-round chainrings have made them much more palatable to the mass cycling market. Having said that, is there scientific proof of their efficacy?

The theory behind Rotor is that their design “increases” the chainring size during the powerful downstroke (e.g. a 53 becomes an effective 56) to maximize torque, while “decreasing” the chainring size (e.g. that 53 becomes an effective 51) during the dead spot at the bottom of the stroke, thus minimizing the time and effort in that dead zone. An unique aspect of Rotor is that this effective power zone can be individually adjusted, as the chainring can be installed at different orientations.

Peiffer and Abbiss 2010
My colleagues in Perth Australia, Jeremiah Peiffer and Chris Abbiss, who I had the pleasure of visiting and riding with in 2009, performed a study on the efficacy of Rotor rings during my visit and published it in 2010 in the journal International Journal of Sports Physiology & Performance (Peiffer and Abbiss 2010).

The concept and research design is very straightforward: have cyclists perform a 10 km TT using round or Rotor rings in one of two orientations. Specific details:

• Nine trained male cyclists with VO2max of 64.1 mL/kg/min and a peak power of 450 W during a graded exercise test participated.

• A familiarization 10 km TT was performed with round (53T Dura Ace) chainrings.

• All TTs were performed in a thermoneutral (24oC) lab on a Velotron ergometer, with a powerful fan providing 32km/h wind.

• The Round condition was again with a 53T Dura Ace chainring.

• The E1 condition was with a Rotor Q-Ring, with the major axis set at 110o counterclockwise to the crankarm.

• The E2 condition was with a Rotor Q-Ring, with the major axis set at 100o counterclockwise to the crankarm.

• Subjects were blinded to the condition (chainring area was covered with a guard), and no performance data was provided until the completion of all trials. During each ride, the only feedback provided was distance completed.

I always like it when studies are clear in their goals and simple in their designs. One strength is definitely in the blinding of conditions and withholding of performance data, as these helped to ensure that subjects didn’t start with any pre-conceived performance templates based on their prior experience or biases towards non-round chainrings. Having used Rotor rings myself on one of my bikes for many years, I can attest that, during normal seated riding, it’s not overly obvious that you’re riding non-round rings, so I doubt that the subjects could tell what they were riding.

Riding Round in Circles
So what were the main findings?

• During the 5 min at 150 W and 5 min at 200 W warmup, no differences were observed in the cycling economy (calculated as watts per litre of oxygen consumed), heart rates, or ratings of perceived exertion.

• The primary result was no difference in average power output across the 3 conditions, with 340 (Round), 342 (E1), and 341 (E2) W. This meant that any difference was less than 1% across conditions. Even in a sport where “every second counts,” it would be hard to claim any statistical or practical benefit given the ~30 W standard deviation.

• Expanding on the above, while individual data showed that many cyclists had a slightly improved performance with a Rotor chainring, only 4 individual trials exceed a 1% improvement compared to the round chainring.

• Breaking the data down into 2 km intervals, again no differences were seen across conditions in average power and cadence. With the E1 condition, heart rate was slightly higher (174 bpm compared to 171 bpm) compared to the Round condition.

The data overall does not seem to support any performance benefits from using Rotor chainrings compared to round chainrings. The strength of this research design was that it used a cycling relevant test of a 10 km time trial, which simulated pretty closely what cyclists would do in real life. One idea proposed by Peiffer and Abbiss is that the lack of difference may be because the Rotors are NOT sufficiently non-round, as prior mathematical modeling suggests that the optimal eccentricity for non-round chainrings may be 1.29 rather than the 1.1 from the Rotors.

Additionally, the caveat is the high individual variability across the nine subjects. Only two of the nine subjects had lower performance with the Rotors compared to the round chainrings. Furthermore, four of the nine did increase their performance above 1% compared to the round chainrings. The conclusion to draw then, appears that, while we should take overall claims of efficacy with a grain of salt, there is still the possibility that our own individual characteristics may make non-round chainrings of benefit.

Ride safe and have fun!

Peiffer JJ, Abbiss CR (2010) The influence of elliptical chainrings on 10 km cycling time trial performance. Int J Sports Physiol Perform 5: 459-468

Comment from Pablo Carrasco, Q-Ring designer and Rotor co-founder:
About your article I would like to clarify my point of view.

Q-Rings shape and recommended orientations are based in the whole Newton equation which includes the forces we can put in the pedal at every angular position but as well the inertia variations during every single downstroke while pedaling, considering the inertia not only from your legs (moving like pistons or so), but as well the whole cyclist’s body and bike.

Of course this study shows no results if you race in a Velotron ergometer using a Q-Ring oriented 100 and 110 degree, but not about a real cyclist in the road using a proper orientation for the oval depending of the rider. Different inertias involved would mean different orientations for sure.

Q-Rings natural principle is that you don’t have different power (just what your cardio system brings to your muscles), but because your muscles act in a softener manner (modulating for less force oscillations), your fibers suffer lower peaks of tension, and this way fatigue (mechanical fatigue related to cycles & peaks of effort) may appear later during the extreme racing efforts, allowing you to maintain your high power longer, and so, performing at the end a better total output.

Best regards,

Pablo Carrasco
ROTOR co-founder

About Stephen:
Stephen Cheung is a Canada Research Chair at Brock University, and has published over 50 scientific articles and book chapters dealing with the effects of thermal and hypoxic stress on human physiology and performance. He has just published the book Advanced Environmental Exercise Physiology dealing with environments ranging from heat and cold through to hydration, altitude training, air pollution, and chronobiology. Stephen’s currently writing “Cutting Edge Cycling,” a book on the science of cycling, and can be reached for comments at .


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