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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?
