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I knew my oval chainrings were probably over-estimating power readings from the bePROs that I have used for a long time. Perhaps the bePROs have lost a bit in calibration over the years? Or not? Either way, with a new KICKR v3, new Favero ASSIOMA DUOs and a new, factory installed/calibrated WatTeam Powerbeat (Dual) I decided to have a little play to see what effect ‘ovals’ might have.
Setup: Front inner circular chainring and front outer oval chainring – a ROTOR Q-RING on an aggressive ‘5’ setting. This was following a workout on the KICKR targeting 4x repeats of [5mins@201w, 5 mins@219w]. Cadence & Chain Ring parameters varied as shown in the table below to cover all combinations. PM calibrations/spindowns were completed prior to starting the ‘test’. This was an aerobic effort so pedal stroke should have been reasonably consistent. Indoor temperature was approx.18 degrees.
EDIT: Make that 80 minutes with 3x PMs, test re-done, below. I messed up there and had the KICKR set incorrectly, essentially showing target not actual (sigh, ty dc). Results TOTALLY different
The intention was twofold to get an indication if:
- My Q-RINGS caused my pedals to over-state power (Favero state this IS the case).
- If power was over-stated then was there a further effect influenced by cadence
Here is a chart of the powertracks overlaid with no smoothing, luckily the PowerBeat dropped out on the warmup:
The very last interval for the WATTEAM PowerBeat was wrong as the Edge turned itself off in protest at a few drops of sweat on the touchscreen #EpicGarminFail.
| Target <85rpm or >97rpm | Chainring | KICKR Target 201w or 219w | ASSIOMA watts | +/-%KICKR | PowerBeat watts | +/-%KICKR | |
| Int 1 | 82.5 | circular | 200.1 | 198 | -1.0% | 195.3 | -2.4% |
| Int 2 | 82.9 | circular | 219.8 | 217.5 | -1.0% | 212.5 | -3.3% |
| Int 3 | 96.9 | circular | 201.5 | 202.5 | 0.5% | 195.1 | -3.2% |
| Int 4 | 97.3 | circular | 219.2 | 220.8 | 0.7% | 210.4 | -4.0% |
| Subtotal | 210.2 | 209.7 | -0.2% | 203.3 | -3.2% | ||
| Int 5 | 84.3 | oval | 202.4 | 208.9 | 3.2% | 197.6 | -2.4% |
| Int 6 | 83.4 | oval | 219.7 | 225.6 | 2.7% | 214.0 | -2.6% |
| Int 7 | 97.8 | oval | 201.8 | 209.9 | 4.0% | 195.3 | -3.2% |
| Int 8 | 99.3 | oval | 218.9 | 223.3 | 2.0% | 209.1 | -4.5% |
| Subtotal | 210.7 | 216.9 | 3.0% | 204.0 | -3.2% | ||
| 7.2 | 3.2% | 0.7 | 0.1% |
Note: Not a scientific test
Tentatively I would draw these conclusionettes:
- PowerBeat understates equally regardless of chainring type (the latter as stated by WatTeam)
- ASSIOMA appears “accurate” with circular rings but overstates by approximately 3% with ovals (stated by Favero as 2-4%)
- Cadence cannot be said to affect any over/understatement of power with ovals
I would also ask, “Where is the drivetrain loss?”
I suspected that ovals might be overstating my power by 15w at higher levels than in this test. Hopefully that’s not the case.
QUESTION: Should I leave my power outputs as they are with the ASSIOMAs and probably delude myself at how wonderful I am (joking) or should I knock 3% (7w) off? If so, how much?
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Great, but difficult subject. ? Some thought’s…
The
dilemaissue with this test (non-scientific, as declared) is… we have three powermeters and we highly suspect that one must the good one and two coop not that good with the ovals. But which one? Maybe all three are ‘bad’, as none of them is ‘certified’ (approved) for ovals.2% difference in accuracy is already ±4W@200W, ±6W@300 and 8W@400 – one PM @ -2%, the other PM @ +2% is 8W difference (12W@300 and massive 16W@400) for the same effort/activity.
From my reading, ovals make us more efficient (=less HR at same watts, more watts at same HR, less fatique/strain for same watts, therefore more oompf in the legs) by 5-6%.
…we need a 2IP (as reference PM) to test (verify/validate) the other PMs.
yes I knew I was never going to get anywhere near scientific. I just wanted an indication on how to downgrade the power in my bePROs…that’s the next step for me personally.
I do have a rotor inpower but only onesided!!! i’m not even thinking of wasting my time with that comparison
re your comment on ovals making us more efficient (I probably agree) but it’s not a relavent point. am I missing something??? more absolute power in the legs from a more efficient pedal stroke will still be detected by all 3 PMs
plus they can’t all be bad with the ovals. the ovals and the kickr are the “control” as the ovals will nor affect the kickr which is effectively power on the ground/wheel
Yes the kickr COULD be ‘absolutely’ worng but the control against that is to match it to the ASSIOMA/WATTEAM with circular rings. two of them match and so it is not unreasonable to assume they are almost correct (to manufacturer tolerances)…at least not for the purposes of what I am doing here.
I found your single legged 5’@200W warmup-intervals quite impressive. (You did ask for some annoyance, right? ?)
Good. Onesided does not count as ‘valid tool’ – except you do more one legged sessions.
The problem are the ‘micro(a|de)ccelerations’, caused by the ovals. Only PMs with a high ‘sampling rate’ can take those micro(a|de)ccelerations into account.
The micro(a|de)ccelerations go (a bit smoothed) via chain to the rear hub. I haven’t had a KICKR, so I don’t know how it handles it and if it could be used a valid ‘control’ – I have doubts. Even Cyclus2 had (or still has?) issues with ovals.
(Annotation: From my testing with NEO and different PMs, I know, that none of the PMs did take into account when I was riding over dirty roads with activated roadfeel – but my legs did feel the increased effort and Tacx NEO did show the increased effort too. The NEO is able to do the ‘roadfeel stuff’ beause of this his very high sampling rate. From my testing I think the Neo could possibly be used as valid ‘ground control’ But to be sure I would need a 2IP to validate that/my ‘impression’.)
i can’t remember exactly but I looked into the sampling rate more than a year ago. And there were several PM s that had the same rate as the ROTOR inpower. so I assumed it was more than just the sampling rate. (or my memory is fading)
Ps. yes glad you spotted the extended one-legged drills at the start.
For my setup it looks like this:
Currently you have the KICKR set to transmit the ‘stated’ power, and not the ‘actual’ power, which is why the line looks so perfect. It’s a settings option under sensors in the Wahoo app.
well that’s annoying.
thank you.
Yeah, drives me crazy. It wasn’t an option last year when the 2016 KICKR launched, and everything looked too perfect. After some whining they made it an option so that you can see actual power. But I always get bit by it the first time I ride a new KICKR (like a few weeks ago). Grr…
It’s really a helpful tool. Works pretty well. But needs a ‘no download of data sets’ option for public links.
yes and what’s even more annoying is that the end game is going to end up me paying you to use your analyser ? although I do have 2 more convoluted workarounds to get overlaid power averages (maybe 3) but not overlaid cp charts (GC?)