Quote:
Originally Posted by MetroMPG
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If the user doesn't attempt to control for external variables as much as possible (eg. speed, grade, road surface, vehicle weight, wind, engine/drivetrain temperature, traffic, other vehicles' effects on your aero, cruise control vs. driver's right foot, etc. etc.) then comparisons between state A & B are suspect, regardless of the measuring tool.
Just saying.
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Yes, there are a lot of things that can mess up the quality of the data but there are some things you can do to make the most of the time invested.
Some smart guys (like R Chung and A Haile) have come up with methods to account for accelerations, grades and kinetic energy when regressing power on speed in order to derive Crr and CdA. These methods utilize the fact that a loop has zero net elevation change. With several laps of varying speeds, one can calculate which constant force and which F=k*v2 best describe the work/energy measured by the power meter
on a per sample basis
The real enemy is wind. All other factors can be handled with a good testing protocol, a good venue and accurate sensors for mass, torque/force, speed, temperature and humidity. This has been proven many times by many guys with power meters on their bikes.
I see no reason why this wouldn't apply to motor vehicles also, in fact I think the data could be even "cleaner" since the speeds with a car are 3-4 times higher
so any wind would be less influential.