Originally Posted by
mollusk
The "velocity" in the drag part is the relative wind speed. In WR's example that would be 27 mph converted into nicer units. The "v" in the power = Fv is the ground speed. The power is your rate of work as measured with respect to a reference frame fixed in the ground.
Say you were now not moving relative to the ground with a 2 mph headwind. While there is a drag force on you you are not doing any work because the "d" is zero.
Nice catch, thanks.
Originally Posted by
echappist
Which brings up the next question: what is the assumed velocity in the drag force part of the equation? Every manufacturer interested in aero publishes nice look graphs of drag force vs yaw angle, but rarely do they mention the assumed relative wind speed.
The reason why i'm asking this is that FLO is apparently coming out with aero wheels that are around $800 for the pair and uses aero shaped rims.
Without them stating it, you don't know. Email the mfgrs and ask them to substantiate their claims. I did that with Cannondale because they claimed that their frame stiffness lost less power than other frames. They came back with "well, we didn't measure it, because that's difficult, but it's intuitive." Ummm, yeah. Ok. Never mind that it's difficult to measure because the difference is so small that it's immeasurable.
Anyway, if the wheel mfgr doesn't post test data, you should ignore their claims, in my opinion. They may have tested at 160mph behind a 747 engine to inflate a drag difference.
Regarding the money spent vs. the power saved, it will never add up. It's going to be expensive and will only add an incremental results benefit. That's not the point though. If you want to go as fast as you can, and you have the means, you have to buy some wheels.