djmercer wrote:
RChung wrote:
Was this a standard Computrainer? The CT is a relatively low inertia trainer. That's why Racermate also makes the Velotron, which has a humongous (that's a technical term) flywheel. The effect we're talking about isn't going to be easily spotted on a low inertia trainer, but you can see it on the road where inertia is high.
Robert, it is a CT Pro.
For Robert, Watt Matters and other über techies: I think we need to differentiate the people such as yourselves who are capable of spotting an nth Watt difference here and there for purposes beyond simply riding a race with an even effort. For that, all your concerns and efforts to get the minutiae of each newer PM, be it Stages, Vector or the P2M are infinitely appreciated but beyond the scope of the 99th percentile and under. When the thread started to screech through a side alley, I chimed in with the reality check about end-user functionality with the P2M with round vs. oval, because for the purposes of hitting the road, the data is good (enough) and the manufacturer's claim appears to be valid. Anyhow, as fellow pocket protector sporter who loves the details, carry on......!
Edit: Apologies Watt M. I thought you were referring to P2M rather than Stages. No matter. The comment about head stability was due to my interpretation that there would be an indication about the unstable rotational velocity reflected in the head unit if it were so. My mistake as obviously I was wrong!
Dave
Well...let's put this in perspective then...with the exception of Quarq (who admitted it would be an issue when asked up front), a representative from basically EVERY PM manufacturer that could potentially suffer from the "non-round ring inflation factor" has initially stated that using the those rings on their product would not affect the power readings...only to be shown later to be mistaken.
So...until shown otherwise (I'm sorry, but your anecdote doesn't qualify) or P2M decides to tell us the answer to the simple (and non-proprietary) question "Do you assume constant crank angular velocity within a pedal stroke when making your power calculation? i.e. is your power calculation "event based?" the prudent thing to do would be to assume that they too don't fully understand the issue.
It's not a tiny issue we're discussing either...for a ring with the ovality of the Osymetric, we're talking about a 4% inflation of the power level. At an FTP of 250W, that's a 10W error. If you don't think you need better accuracy than that, then save your money and get a PowerCal instead. Or, just train and pace with an inexpensive HR monitor. Why bother with the expense and compromises (for some) of a power meter?
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