Introduction
Several of my
riding companions have recently experimented with non-circular chainrings. As
an anecdotal observation, most of them report a performance improvement and
none have reverted to their original circular rings. There have been several well-publicized results
on non-circular chainrings in the last few years, most notably the Tour de
France wins by both Bradley Wiggins and Chris Froome. Interestingly, however,
Tim Kerrison, head coach at Team Sky, claims that credible research that has
been undertaken is inconclusive. The question then arises: are these scientifically
proven benefits or a placebo effect? This
article attempts to summarize current thinking with the disclaimer that I have
not yet tried non-circular rings myself.
Concept
The idea is
very simple: design and orient chainrings that allow the rider to spend less
time in the least powerful parts of the pedal stroke, when the cranks are
vertical, and more time in the most powerful parts of the pedal stroke, when
the cranks are horizontal to the ground. That is, minimize the negative effect
of the so-called “dead spot” which is the point at which the cranks are
vertical and neither leg is generating any significant power.
The single parameter
that captures this idea is known as “crank angular velocity” which remains
relatively constant throughout the pedal cycle with circular chainrings. A non-circular chainring varies the crank
angular velocity within the pedal cycle which, in turn, alters the time spent
in each segment of the pedal cycle. To translate this into practical terms, the
chainring should have a larger radius at the stronger segment of the pedal
stroke and a lower radius at the weaker segment.
Bicycle
engineers have been aware of the dead spot for over a century; non-circular
chainrings were first tried back in the 1890s. The most notorious experiment in
recent years was with Shimano’s Biopace rings (1983 to 1993). Recent studies claim
that the downfall of Biopace was caused not by the shape of the rings but by
their orientation.
There are
several parameters that are relevant in non-circular ring design: the number of
teeth, the “eccentricity” of the rings (the ratio of the major axis to the
minor axis) and their orientation relative to the crank arms (including
adjustability that allows rings to be “dialed-in” to the specific rider and
bicycle set-up). The various manufacturers
of non-circular rings, for example Rotor, OSymetric, Bionicon and Absolute
Black, all put their own particular spin (is there a joke there?) on the
different variables.
Research
There have
been a myriad of papers written on the subject, not all of them independent and
unbiased. Researchers have examined the
physiological and performance differences between non-circular and round cranks
on numerous occasions. Though there are some that report improvements of up to
6% with non-circular chainrings, a majority have concluded that, for efforts
longer than one kilometer, there’s not much difference between round and non-circular
chainrings. None reported a decreased performance. Additionally, not all
authors are even agreed on the appropriate output parameters to be measured: speed, power output, lactate threshold, heart-rate
etc.
In support of
the use of non-circular rings for high-intensity events, an IJSSE study based
their conclusions on a 1 km time trial study over a six-week period, using
eight competitive male cyclists and triathletes using Rotor Q-Rings.
Performance measures during the time trial were based on time to completion,
speed and power output. In addition, physiological measures (oxygen consumption,
heart rate, blood lactate were also monitored over the time span of the
study. The authors concluded that the
Rotor Q-Rings provided a positive effect in the time trial and speculated that
they could also prove beneficial in criterium-style racing events or at the end
of a road race in which bicycle racers typically pedal at similar intensities
and durations as the 1 km test. (“Effects
of Chainring Type (Circular vs. Rotor Q-Ring) on 1 km Time Trial Performance”.
Christiane R. O’Hara et al. International Journal of Sports Science and
Engineering. September, 2011).
However, more
recently, The Journal of Sports Science and Medicine published an article which
documented extensive testing for blood lactate, power output and oxygen
consumption but concluded that non-circular chainrings did not produce statistically
significant differences over round ones. (“Physiological
Responses during Cycling with Non-circular Chainrings and Circular Chainrings”.
Alfredo Cordova et al. Journal of Sports Science & Medicine. May, 2014)
Studies at
the University of Utah, while not challenging the fundamental premise behind
the use of non-circular chainrings, addressed the issue from the perspective of
joint-specific kinematics. The author concluded that use of non-circular chainrings
did not either enhance or compromise joint-specific (collectively, the hip,
knee and ankle) performance in trained cyclists. (“The Influence of Non-circular Chainrings on Maximal and Submaximal
Cycling Performance”. Chee Hoi Leong. Department of Exercise and Sport Science,
The University of Utah. December 2014).
Conclusions
The anecdotal
evidence in support of non-circular chainrings, though not compelling, is
certainly intriguing. Perhaps they are at the same stage of development and
general acceptance as clipless pedals, integrated shifters and mountain bike
suspension were in their early days …. innovations that are now regarded as de rigueur.
Nevertheless,
it would appear that objective scientific experimentation in support of the use
of non-circular chainrings is somewhat lacking and there is unquestionably no
measure of consensus among the various researchers. At the end of the day perhaps we need to just
accept that even a placebo has the potential to offer a significant performance
gain.
Some challenges
If you decide
to give non-circular chainrings a try, be aware that:
·
Not
all of the various manufacturers’ non-circular rings fit all cranks. Be sure
you understand your crankset’s spider pattern, bolt circle diameter etc.
·
All
front derailleurs are optimized to work with round chainrings and some
degradation of mechanical performance might result with non-circular rings. In
this regard, front derailleur fine-tuning might a tad more finicky.
·
The
risk of dropping a chain appears higher with non-circular rings so consider
installing a chain catcher on the front derailleur.
·
Because
non-circular chainrings change the angular velocity of the crankarms and thus
the power transmitted to any power-meter strain gauges that yu might use, any historical
power data from your prior use of circular rings cannot be compared to the data
set from the new rings.
