Slowman wrote:
the power was measured using a quarq power meter on the bike of the sole person on the only bike used for all 96 runs. accuracy? it's the accuracy of a quarq power meter.
OK then...and myself having had quite a long term experience with Quarq PMs (I was a beta tester for them at one time, after all), I also know that the data quality is only as good as the care is taken during their use. It's imperative that the torque slope is checked (and adjusted, if possible) and to "zero early, and zero often" ;-)
Slowman wrote:
because speed was constant for all runs. drivetrain losses are not material to because the actual power is not relevant (who cares how much power it takes a given rider to ride his bike at 20mph on a rolling road?) the only thing that's relevant is the delta in power between the set-ups....unless drivetrain losses are changing across the runs, that is. Are we SURE gear selection was the same? You appear to assume it was because the speed was fixed, but is that the case? I don't know...there's no data showing one way or the other.
Additionally, how "fixed" was the speed, i.e. what's the +/- on the speed setting? Did they calculate Crr for each run (which would cancel out speed and power variation), or just compare watts? In other words, if you want to compare "delta power", you need to compare on an apples to apples basis. For roller testing, I don't try to tightly control the speed (in fact, I try to control cadence for a given gear combo), but then I use the speed, power, wheel load, and ambient temperature to calculate the equivalent Crr on the flat at 20C ambient. THAT is what gets compared, not the raw test values. That's the thing, if you have a good model, you don't necessarily need to control all the variables, just record their values and use the model.
Slowman wrote:
the surface roughness has been asked and answered at least 3 times in this thread. what is relevant, that i don't know - also mentioned at some length in this thread - is the vibration in the entire system which could - just using my intuition - add to the "roughness" of the road. i think this is worth investigating.Right...and it's been asked for good reason. You say they claim it's comparable...we're all asking "how comparable?" My intuition is telling me that based on the results, there may be some additional compliance and/or damping introduced in the running surface that's different than typical pavement. That's one way that continually lower pressures would lead to lower power requirements on surfaces consistent with typical pavement roughness.
Slowman wrote:
was the same rider used for all the tests? yes. as i pointed out in posts twice above. how does the data differ from field tests? the data, per zipp, syncs well with their fields tests, which they perform at eagle creek park, on a circuit, and which i stated at least twice, both in this thread and i believe in the article on the front page.Right...they say it "syncs well", and yet you said they aren't willing to reveal that data for some reason. It really should be the "golden data set", no?
Slowman wrote:
how tightly is the ambient temp controlled in the test location? again, just my intuition, but in the 25,000 square foot factory where i built my bikes i hit on the idea of setting the thermostat on my HVAC. this has not been mentioned, explicitly, so for those who have this question: zipp's rolling road is inside its building, not outside.Yeah...see, that's the thing...even HVAC systems can have quite a wide range (relatively speaking) of temperature swings throughout a day. I often run long-term thermal tests at my office and detect local temperature swings in particular areas of the office of a few degrees C. That's plenty of temperature change to affect Crr results, especially if one is looking to resolve them to within 1W (as their plots imply). So, if they aren't monitoring the temperature, and/or compensating for the temperature effects on Crr...well, that throws up some red flags to me.
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