Prove that oval chainrings do work? Getting extra watts for free?

Triathlon Forum
1

The idea of oval chainrings has come and gone many times in the last 30 years but lately more and more pro’s are riding oval chainrings like Rotor or O.symmetric. But is there any evidence that it works? Is it possible that a cyclist can generate more power with an oval chainring? So far I have not read any proof that it might work. This month an article has been published in The Journal of Sports Science & Medicine about the rotor crank (not chainrings) and their conclusion was that the rotor crank did not work.

It made me think about the possible advantage of the oval chainrings.

Who knows the theory about the oval cranks and can explain to me if they work or not?

What I think about possible advantages:
At the optimal range of the pedalstroke there is no benefit because we use our derailleur to select the optimal pedalspeed and force and with both chainset options (oval or circle) we can select an optimal gearratio.
If there is any advantage, the advantage’s is probably at or around the deadspot in the pedalstroke. Around the deadspot the oval chainring has a “lighter” gearratio that with the same pedal speed (as on the normalchainring) requires less torque and produces less power but with an increased pedal speed it is possible to deliver the same power output. With the ligther gearratio near the deadspot and the increased pedalspeed compared to a normal chainring your foot has a shorter time at the deadspot. So you have relative more time at the optimal pedal stroke range than with an normal chainring. Can this be an advantage of the oval chainrings? Or will the increased pedalspeed at the deadspot make you suffer? Or does the pedalspeed not change at all?

2

I trained and raced (some TT’s and a couple of ultras) using Q-Rings. The biggest thing I noticed was when I dropped off my cadence on a climb it was easier to accelerate but unfortunately it was also easier to stay in the lower cadence and grind it out. Based on overall speeds, comparing oval and round seasons, there was no significant change.

3

+1

I think their advantage will come during out of the seat climbs…or 60rpm seated grinds.

4

agreed
.

5

But why? And how can we explain it?

6

But why? And how can we explain it?

At slower RPMs with greater power demands, the amount of power necessarily applied (and the time spent) through the dead spot is increased enough to allow for the bicycle to actually decelerate slightly when power drops off at 12/6 o’clock.

If you look at the power graph of ANY cyclist, the amount of power our musculature can apply to the pedals at the top/bottom of the pedal stroke is rather minimal…when the cycling conditions require a certain power output to avoid deceleration…and that power output required is higher than our bodies put out, then we slow down for a given power output…or we need to use more power to maintain it due to the need to re-accelerate the bike during each downstroke.

The eliptical rings allow the feet to roll through that dead zone faster resulting in less deceleration of the bike during that time.