What's Cool In Road Cycling

Researching The Efficiency of Rotor Chain Rings

After a few years of gaining a gradual foothold in the pro peloton, non-round chainrings have gone big-time, first as unbranded chainrings for Carlos Sastre’s 2008 Tour win, and now as a major sponsor for the Cervelo TestTeam. True to its Spanish roots, a new study from a Spanish research group investigates their efficacy.

Round and Round We Go
Ask any swimmer who spends years and years working on their swim stroke, and it becomes obvious how important it is to maximize the efficiency of a movement as repetitive and continuous as the pedal stroke. We’ve written numerous times in Toolbox about the concept of efficiency, such as a longitudinal analysis of Lance’s aerobic capacity and efficiency from 1993 through to his first Tour victory. Notably, his evolution from Classics hunter to Tour demolition machine was marked by an incredible increase in efficiency, such that his metabolic demands at set wattages decreased substantially through the years.

Improving the neural recruitment pattern of the pedal stroke has been one approach to improving pedaling efficiency. This has led to such drills as pretending to scrape mud off your shoes to enhance pulling back on the upstroke, one-legged pedaling, riding fixed gears, and crank designs like the PowerCrank. Another approach is to alter the chainring design to mechanically enhance efficiency by altering the pedaling stroke instead.

Altering the chainring has not been a new idea, as anybody who rode in the late 80s and early 90s remember Shimano and Biopace. That design, despite the massive manufacturing and marketing clout of Shimano, eventually died off largely because the pros simply would not accept it.

In the past 5-7 years however, a new generation of non-round chainrings have gradually infiltrated the pro peloton, led by riders such as Bobby Julich’s use of the o-symetric chainrings from France. Since Bobby’s first use, o-symetrics have gained a cult following for both time trials and regular racing use amongst pros, including the recent adoption by Bradley Wiggins at the Giro this year.

The Rotor Revolution
The other big player in the non-round ring game is Rotor from Spain. They too have targeted pros first and foremost. Their first huge splash was with cross/road/track star Marianne Vos, who has won on all disciplines with Rotor rings. Following up this success, their biggest coup has been the use by Carlos Sastre during his triumphant 2008 Tour victory as an unbranded chainring on their otherwise FSA sponsored cranks. With Sastre’s move to the new Cervelo TestTeam (CTT), Rotor became the official cranks/chainring sponsor for the entire team, giving them huge credibility and pro access for testing their design.

Apart from the specific shape of the Rotor rings, another unique Rotor design feature is the multiple installation possibilities. Namely, the chainrings can be installed at various positions relative to the crankarms, essentially phase-advancing or delaying the peak of the power stroke. Therefore, the ring position can be adjusted individually based on both personal biomechanics and the demands of the discipline.

The chainrings themselves are just one component from Rotor, and are an extension of their original concept of an improved pedaling system. Rotor started out as a designer of a unique crank system where the arms are not fixed at 180o apart, with the aim of minimizing the dead spots at the top/bottom of the pedal stroke.

Secondly, the chainrings are not perfectly centred on the cranks (i.e., the chainring and crank rotation axis are not one and the same) but can be varied, with the effect of altering the crank angle at which the effective crank arm length is maximal (i.e., where the most force can be applied). Again, this is with the goal of optimizing and matching to where the human leg can biomechanically produce the most force. The chainrings that we now commonly see are an offshoot of the whole system design to enhance acceptance by cyclists who might balk at the different setup and higher weight.

Pro Testing
Obviously, apart from being cool and now being accepted by Euro-pros, the most important question is whether there is any scientific basis for enhanced biomechanics and efficiency from Rotor rings. A 2009 article in the European Journal of Applied Physiology sought to answer that somewhat elusive question.

• With Rotor increasing gaining greater pro acceptance, their clout and contacts likely assisted the research group into getting fifteen professional cyclists from a Spanish continental team as subjects. As we’ve noted before when talking about optimal cadence, it can be very difficult extrapolating data from non-elite athletes to those of top-level athletes, so this access to pro subjects enable an “apples to apples” comparison.

• None of the subjects had any previous experience with Rotor cranks or rings. This is both a good and a bad thing. The good is that the data is not confounded by previous experience. The bad is that, if no benefit is demonstrated, it can always be due to lack of experience and ultimate adaptation to the Rotors.

• Elite athletes are very difficult to test through much of the year, as their fitness fluctuates wildly with racing schedules. This study was conducted during the preparatory period in December, so all the subjects were at a fairly stable period of fitness throughout the study.

• For testing maximal aerobic capacity, an incremental maximal ride to exhaustion was conducted with both normal and Rotor cranks with the crank angle set at 128o (position 3). The subjects were free to select their preferred gear and cadence in the first trial, but replicated that pattern in the second test. This was a nice design to avoid confounding factors from different gears and cadence causing different muscle fatigue.

• For quantifying aerobic efficiency, subjects performed, in a single experimental session, 5×10 min sustained efforts at a power output of about 75% VO2peak. In each effort, they used either the control cranks or the Rotor set at positions 1-4 (crank angles 116, 122, 128, 134o, respectively).

• For testing anaerobic capacity, subjects performed a 30-s Wingate sprint test with each of the 5 possible crank options (normal cranks plus the Rotor positions 1-4).

Data Data Data
Overall, the experimental design was quite well-done in my opinion. The researchers chose professional cyclists, tested a variety of efforts ranging from aerobic, aerobic capacity, through to anaerobic. This is different from many studies which only use one specific test, making it difficult to extrapolate results to the full range of performance requirements in cycling. Lastly, they tested all different options for the Rotor to test whether the adjustable crank angle feature can be beneficial. What did they find?

• No differences in ventilatory threshold or any other parameter was reported between the normal and Rotor (position 3) cranks during the incremental test to exhaustion.

• Similarly, no differences in any parameter was reported in the submaximal test across the five conditions. Importantly, this held true whether all five were compared (normal plus all 4 Rotor positions) or when the normal data was compared to the Rotor position that provided optimal mechanical efficiency results for each individual subject. Adaptation issues aside, this suggests that minimal improvements can be expected with the Rotor cranks during aerobic exercise.

• The primary source of difference was with the Wingate test, which is strongly reliant on massive force output and anaerobic capacity. This tests a whole different range of muscle and biomechanical requirements compared to the aerobic tests due to the much higher power.

• With the Wingate test, Rotor peak and mean power values were consistently higher (4-9%) than normal cranks regardless of which position was used. Statistically, the main significant differences were observed with position 4 (134o angle), and somewhat with position 3 (128o). 68% of the subjects achieved the highest power values with position 4, with 25% achieving the highest values with position 3.

So Round or Not Round?
The main ideas proposed for why the Rotor system worked best on the anaerobic test revolve around the biomechanical requirements with such high power outputs. Specifically, the greater leverage due to the longer effective crankarm length with the Rotor design, combined with the lower negative momentum during the upstroke (due to the lower effective crankarm length, may only really come into play at these high power outputs

Taken at face value, it’s hard to summarize better than the authors in the Discussion: “Rotor System is able to improve the anaerobic performance during the Wingate anaerobic test, but seems not to be able to improve either aerobic power (measured via the VO2max) or aerobic cycling efficiency (measured via the gross mechanical efficiency and the cycling economy) in professional cyclists when compared to control.”

The caveats, as implied above, is cycling experience, and whether aerobic adaptation will occur with sustained use of the Rotor system. That is inherently almost impossible to scientifically test except on an individual case study basis, and is hugely confounded by an athletes natural improvement irrespective of an individual manipulation like the Rotor.

At the end of the day, the important thing to keep in mind is that aerobic parameters were essentially identical with the Rotor system or with normal chainrings. This means that, while the Rotors didn’t provide a benefit, they also didn’t handicap the riders either. The main technical drawback would thus appear to be their heavier weight (by ~350 g, according to the authors). But if that’s not a consideration or concern, and if the weight can be reduced, then it’s potentially the case where it won’t hinder you for the bulk of the race, but will give you a 4-9% improvement when the smack comes down hard, which is often when you need the help the most. Therefore, keep tuned!

Have fun and ride safe!

Rodriguez-Marroyo, J.A., J. Garcia-Lopez, K. Chamari, A. Cordova, O. Hue, and J.G. Villa. The Rotor pedaling system improves anaerobic but not aerobic cycling performance in professional cyclists. European Journal of Applied Physiology. 106:87-94.


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About Stephen:
Stephen Cheung is a Canada Research Chair at Brock University, with a research specialization in the effects of thermal stress on human physiology and performance. He can be reached for comments at [email protected] .

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