Oval chainrings have been around since nearly the advent of chain driven bicycles. The concept is simple; the chainring is at a larger radius when you are at a stronger portion of your pedal stroke and at a lower radius at a weaker portion. But does it actually make a rider faster or more efficient? Or is this another gadget designed to separate you from your money?
Myriad of Claims with Oval Chainrings
The claims are myriad with oval chainrings: it’s easier to turn over a higher cadence, your lactic acid production will be lower, you will access your stronger pedaling muscles while resting your weaker muscles, your overall power will increase (7-10% according to Osymetrics!). If it sounds too good to be true, it usually is.
Notable Results on Oval Chainrings
There have been a few notable results on oval chainrings in the last few years. The two biggest results to date are Bradley Wiggins winning the Tour de France in 2012 and Chris Froome winning in 2013 and 2015. Both rode for Team Sky, a team that is known for its search for marginal gains. Since that Tour victory, Wiggins has switched back to round chainrings. The truth is that people have won all sorts of races on all sorts of equipment with dubious benefits. There is a psychological edge if someone believes in the equipment they are on. If a rider believes that oval chainrings give a boost in performance, they may ride with a bit more confidence in their abilities. People have lucky socks. Why not have lucky chainrings too?
“These are people that are racing for their income. Teams would be clamoring for them because they need to get the best results possible for their programs to continue.”
An argument from some proponents of oval chainrings is that it is much easier to manufacture round chainrings and that is why we don’t see more oval chainrings on bikes. This isn’t the case anymore, though. Oval chainrings are readily available. If the benefits are what they claim to be, we would see many more professionals on oval chainrings. These are people that are racing for their income. Teams would be clamoring for them because they need to get the best results possible for their programs to continue. This is not the case; a few riders are riding oval chainrings because they feel that it’s what’s best for them. There is plenty of off-label equipment in the peloton but there are not a lot of oval chainrings out there.
Research on Oval Chainrings
There have been few peer reviewed research studies on oval chainrings. The Journal of Sports Science and Medicine published an article in May 2014 with the results of a test on twelve elite male cyclists. They tested for blood lactate, power output, and oxygen consumption with no discernible differences. The oval chainrings did not produce a scientifically significant enough difference over the round chainrings in a maximal sprint test to put the results outside the margin of error. Another claim is that oval chainrings allow for a lower metabolic cost than round chainrings which the study also found not to be true.
Another peer reviewed study from December 2010 tested cyclists in a 10 kilometer time trial. This study also found similar power output and rate of perceived exertion between round and oval chainrings. It also found that heart rate was statistically significantly higher with the oval chainring versus the round chainring which is contrary to the claimed benefits of oval chainrings.
This January 2004 test also did not find conclusive benefits to oval chainrings. They measured ventilation, oxygen uptake, carbon dioxide output, respiratory exchange ratio, and heart rate with no statistically significant differences between round and oval chainrings.
Installing Oval Chainrings On A Bike
The first hurdle to trying out oval chainrings is to get them working properly on a bike. Every front derailleur on the market is optimized to work with round chainrings. Some oval chainring manufacturers provide shims to move the front derailleur rearward to match the derailleur cage with the curve of the chainring. It will help with shifting but the chainrings themselves are optimized for their bio-mechanical claims, not shifting performance. Furthermore, there should also be a chain catcher on the front derailleur to keep the chain from dropping off the inside.
Shifting Performance Compromised
Thinking about your shifting performance in the heat of a critical moment is not ideal. Will the chain flawlessly go up to the big ring right at the crest of the hill? Will the chain fall off to the inside just as the big climb starts? Couple that with the cost of an oval chainring being on par with the best shifting round chainrings and the benefits become negligible. Nobody ever blamed losing a race on chainring shape but they certainly have on poor shifting performance.
Power Data Discrepancies
A lot of riders have a lot of data from their crank-based power meters. Oval chainrings change the angular velocity of the crankarms, thus changing the power transmitted to the strain gauges, yielding different power numbers than if the same person was pedaling round chainrings. All of that accumulated data (which is very useful for long-term training) is rendered useless. It’s almost as if the data is from two different people; one on round chainrings, one on oval chainrings.
The Take Away
Oval chainrings are a divisive subject. Supporters point to physics to support their claims of greater power through lower effort. Peer reviewed experiments show the opposite and that the benefits are negligible at best. There is no question that the mechanical operation of the bike will suffer. A finely tuned bicycle with round chainrings will always shift better than the same bicycle with oval chainrings. Switching round for oval chainrings will also make years of power data useless for comparison. But if it gives a rider a mental edge, it all may be worth it.