Oval Chainrings and power differences when using a trainer for power?

Hey All,

I just got a bike with a qring chainring setup on it which i’m planning on using on my tacx neo2 for my TR sessions. As i’m using the tacx as my power source, anyone know if that’ll impact my power numbers?

I’ve seen a bunch of posts regarding oval chainrings giving inflated numbers, but as my power source is the tacx will it matter?

thanks!

Hello,

I use oval rings on an H3 and the power numbers are pretty consistent across Quarq, Stages, and Vector 3 readings. They are inflated when the power meter uses average angular speed, but it’s not a massive amount. As long as you have consistent readings, it shouldn’t interfere with training. For example, the Assiomas may give different readings as they claim to measure instant angular speed.

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The post I have just added might help.

Oval chain rings may affect readings but only for some power meters. Since the Neo measures at the hub it will not be affected but the numbers you get should be less than if you had a crank or other power meter that did not factor in drive train losses.

The article below gives a bit more on this but is no longer up to date in one respect in its quote below.

“Here’s the concern: most power meters make the assumption that your pedaling velocity is constant.”

This may have been true in the past and may still be true for cheaper meters like the 4iii. However other meters are much more sensitive and sample the stroke many times during a revolution. So you really cant say “most” but “some”.

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thanks for the feedback! i’m going to set it up and see if there’s any big difference for me in how i ride as i’ve never used oval chainrings.

They talk about some studies here that seem to say it has zero impact on functional power and efficacy. But something about how the power numbers will read higher during part of the stroke but that power is not delivered to the drivetrain. But I might be wrong.

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Hi,
I was recently after some oval rotor chainrings, but having spoken to them and explaining that I use vectors they recommended sticking to traditional chainrings. They couldn’t guarantee the vectors would read power accurately with oval rings.
I had previously been using an aerocoach arc chainring so wonder if my vectors were reading incorrectly with them?

I use oval rings because my right knee is most compromised coming over the top of the stroke and they anecdotally relieve pressure and reduce the constant inflammation. No, they do not help me directly produce more power, but allow me to train harder, and eventually generate more power through better training.

To add some more clarity on the over estimation, when the chain speed is constant, the angular speed of the cranks is fluctuating with oval rings. They are designed to be slowest in the strongest part of the pedal stoke as the radius increases. Power meters that use average angular speed overestimate the angular speed the greatest when the torque is the highest, but underestimate the speed when the torque is the lowest. The overestimate is greater because of the torque distribution causing the offset. If you spin a perfect circle there would be minimal error. If 100% of your torque is concentrated at the highest point, the error would be roughly half the oval percent. If you distributed 50% at the highest point and 25% at plus and minus 45 degrees, the error would roughly be one quarter of the oval percent. Absolute Black lists as 10-11% oval for reference.

The error is fairly predictable and most likely within the range of accuracy of most power meters. As long as you have consistent readings, I wouldn’t be concerned with the error impacting your training.

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That’s slightly strange. Pedals shouldn’t be affected by oval chain rings (at least according to Hunter Allen) a finding I confirmed with my recent test using P1s v 2InPower v Neo (see elsewhere in forum)

It may be they were just being cautious.

I’ve used Q rings for near 10 years now.

I like them just because they give a subliminal feedback cue to apply power early on in the stroke down.

I’ve also used a Leomo motion sensor and WKO4s pedal metrics. On the former my “deadspot” score is 0 and that latter my “wasted watts” is near 0 even at 300W. It may be coincidence but I think that over 100000s of revs of giving the legs a signal of when to start firing a bit harder they just learn to do it a little bit better. It’s only a few watts but its free watts.

Possibly. The Garmin website also has the same warning about oval chainrings.

Used Q rings for a couple of years now and the readings from my Powertap hub & vectors are within a couple of Watts up to around 800W. Easy to test by pairing to different head units/TR app.
Anecdotally my smashed up right ankle is much less sore after riding using Qrings over traditional round ones which at a guess is down to the forces being applied at different points in the pedalling cycle… but what do I know :thinking:

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