Oval-shaped Chainrings: Evidence challenged

Rotor_Cervelo_crankset_Osymetric_chainrings

  The sport of cycling is without doubt one of the leaders in technological innovation, with continual development of bicycle frames and wheels designed to optimize acceleration, power transfer, road vibrational forces, and aerodynamics, to name a few. Few areas of the bike are overlooked, including the crank-pedal interface; i.e., crank arm length, as well as the shape of the chainring. Which is why a recent question, fueled by Business Insider’s late to the party article1, posed online asked whether ovalized (non-round) chainrings are worth their hefty price tag. In this post, I’ll highlight the scientific consensus on these chainrings, and my opinion on whether you want to drop your money on this potential marginal gain.

History Repeats Itself

If you have been involved in the sport of cycling since the 80’s or early 90’s then you’re probably asking, “Didn’t we already try this fad?”

Yup! Biopace rings were all the rage when I started racing in the 80’s, developed through computer-aided design2In reality, however, the concept of elliptical chainrings has been around almost as long as the bicycle. The late Sheldon Brown discussed this on his website:

“Around the turn of the century, shortly after the development of the chain-driven bicycle, someone came up with the bright idea of elliptical chainwheels. The idea was that the large radius of the chainwheel would drive the chain when the cranks are horizontal and the small radius would pull the chain when the cranks are vertical. The theory was that while the cranks are horizontal you can pedal more efficiently, and thus can push a higher gear. When the cranks are vertical, you get a lower gear due to the smaller effective radius of the chainwheel. The lower gear is easier to push, and you get through the dead spot sooner. This looks great on paper, but doesn’t work out so well in practice.”
Biopace was all the rage for awhile, but did nothing for performance.

Biopace was all the rage for awhile, but did nothing for performance.

Computers don’t ride bikes

   As we all realize now, bikes no longer come equipped with Biopace rings because they did not improve performance. So why are elliptical rings back? Well, for starters, people will buy anything if a champion cyclist uses it. However, the new designs are actually backed by some pretty good computer modeling that do suggest that altering the shape of the chainring will optimize power production where the greatest torque development occurs, between 2 and 6 o’clock (figure 1). Now in the interest of simplicity, I’ll skip over many of the technical aspects of mechanical and mathematical details of the design; the 2014 PhD dissertation by Leong give a great deal more detail on this topic.

   In brief, non-circular chainrings are typically designed to increase the time spent in phase where power production is greatest (flexion and extension), while minimizing the time spent in the phases where power production is lowest. In more technical terms, they alter the gear ratio effects, just like your actual gears and crank arm length, and hence the instantaneous angular velocity of the crank arm. This strategy of manipulating the instantaneous crank angular velocity may provide a strategy for maximizing cycling power within the pedal cycle. Theoretical models, like the one discussed by Rankin & Neptune 2012, lead to a chainring design like the one presented in figure 2. Does it actually work?

   As I discussed on Tipcast 90, studying the effects of very obvious equipment changes can be difficult for several reasons, including placebo/nocebo effects, learning/training effects, athlete ability and sport selection, as well how the trials are ordered. Suffice it to say, there are a lot of factors to account for, so simply comparing a couple time trials or hill climbs won’t do it. Incidentally, these are all of the factors that industry ignores when they do either in house testing, or sponsored, unpublished papers; note, I’ve included some of those papers that Rotor cites on website, including one from the notorious Francesco Conconi.

   In keeping with my promise, this will be a short article, because based on the current literature non-circular rings is at best equivocal for endurance cycling; references are grouped according to their overall findings. A handful of studies over the past decade or so have suggested and improvement in some variables like lower HR or improved efficiency. However, the bulk of the studies show no improvement in actual performance. Moreover, a few studies have indicated that the added time spent in the power production phase and reduced time in the recovery increases energy expenditure; this is akin to the Buffalo Bill’s no huddle offense, which was effective for offense, but could leave left the defense fatigued and less effective. In both cases, however, the advantages can be real under specific conditions, but probably are not best when used all of the time. So the overall verdict is that these chainrings simply do not deliver any performance gain, particularly for the hefty price tag.

   Nonetheless, there are some specific and well-documented cases where these chainrings could be beneficial, which is sprinting, particularly sprints lasting less than 10 sec, like in the sport of BMX and 1-km time trial performance, both of which are brief activities which could capitalize on even small increases in the “power production window” but are not impacted by even a large decrease in efficiency. As such, the findings for these groups indicate that:

  • Among BMX riders, elite level competitors were able to significantly increase the distance (+0.26 m) covered in a 4 sec sprint, while novice riders were not. Additionally, both groups produced significantly LESS POWER while using the Q-rings. The authors surmise the Q-rings reduce the time spent in the “dead spots”, which allowed for smoother overall power production. Probably a better way to put it is that power was lower, but was applied longer, so the went further.
  • Among a small group of cyclists and triathletes, Rotor Q-rings significantly increased power output and reduced 1-km TT times, and that they did not require an adaptation period to gain that advantage. They also showed that the Q-rings reduced HR and improved efficiency over that 1-km TT. However, the study was very small, so I would view these results as preliminary.

Why do Chris Froome and Bradley Wiggins use Osymetric rings?   

   It’s obvious that top athletes often use and endorse products that are total garage. Why? Because they’re paid to do it. Actually, sometimes they don’t actually use the product, which is tantamount to fraud, other times they either believe in the product and like it personally. In this case, Chris Froome appears to believe in the product, and perhaps they actually work well with his explosive, high cadence attacking style. However, for the of us, I think Tim Kerrison summed up well in 2015:

“…performance-wise, there is very little in it either way…many of our riders have tried them. Only a few continue to use them…both Wiggins and Froome use them, [so] they are unlikely to be significantly detrimental to performance. The credible tests and research that has been done is inconclusive…Crank-based power measurement systems [e.g. SRM, Quarq] appear to over-report power when using Osymetric rings…In other words, power reads higher, but this does not correspond with an increase in the power actually being generated by the rider.”

   In my professional opinion, there is no justification for endurance cyclists to risk using these expensive rings. I say risk, because Osymetric’s in particularly dramatically increase the likelihood of dropping your chain; I’ve had a few races where a dropped chain cost me a big result, including my GC place at the 2007 Green Mountain Stage Race. However, if you’re in a sport requiring a very short burst of maximal power, with little risk of a dropped chain, like track sprinting or BMX, I’d give them a try.

Footnotes

  1. Late because this story came up about 5 years ago with Bradley Wiggins. The story even showed up again last year on CyclingWeekly, where Sky coach Tim Kerrison actually raised doubts about their benefits.
  2. Biopace rings appear elliptical, but are actually the opposite of classical elliptical design, with the shortest radius oriented at the horizontal, and the large when the cranks are vertical. The design was based on dynamic analysis of pedaling; a bit like choosing running shoes based on running analysis, rather than the foot architecture while standing.

References showing no real benefit

Bini 12 Noncircular Chainrings And Pedal To Crank Interface In Cycling: A Literature Review

Duc 16 O-Symetric

Horvais Et Al (2007)

Leong 14 UNPUBLISHED Phd Oval Vs Round Sub Max And Max

References showing benefits

Gaesser 92 DE Improves

March 12 Does A Non-Circular Chainring Improve Performance In The Bicycle Motocross Cycling Start Sprint?

O’hara 12 Effects Of Chainring Type (Circular Vs. Rotor Q-Ring) On 1km Time

Rankin 12 A Theoretical Analysis Of An Optimal Chainring Shape To Maximize Crank Power During Isokinetic Pedaling

Industry Sponsored Bullshit

Conconi Making Bullshit Claims With No Data – this one is classic Conconi, whose Conconi test is garbage BTW, where he studied four subjects, but showed benefits in only one. He then proceeded to claim they improved performance. 

Rotor Sponsored UNPUBLISHED STUDY ABOUT THE METABOLIC EFFICIENCY OF THE ROTOR® SYSTEM COMPARED WITH A CONVENTIONAL BICYCLE

 

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