Tinea Pedis wrote:
No, this is not correct.
so maybe just more of an eye to your choice of words, and there will be less misinterpretation of what you're looking to say. Especially when I'll disagree on the lack of 'usefulness' you're implying rider-less testing does not provide.
Sorry, usefulness of the testing aside, the statement "without the rider you get a true appreciation for the differences between the frames" is profoundly incorrect and represents a misunderstanding about what is being measured (aerodynamics is a function of both the geometry and the flowfield, not just the geometry).
An easy-to-understand analogous situation is if I claimed to have come up with new saddle covering material that I claim reduces aerodynamic drag by 20% and test this in a wind tunnel without a rider to "get a true appreciation" for the aerodynamic performance of my new material. The results of the test in and of themselves may be sound, but it's a completely worthless result. The rider-vs-riderless frame test is the same, it only differs in degree - you can't, without further testing, differentiate e.g. which components contribute high drag counts in the riderless test and may show nothing like the same with a rider on, and this may well differ between frames. The picture on the test title page is the dead give-away - the smoke trail passes round the front wheel nicely and then, oops, goes exactly through the kneecap of the right leg and then, oops, continues unimpeded through the frame to impact the kneecap of the left frame. Are those missing legs going to impact the flow on the downtube and seatube, and even the front fork? Sure they are! Given the radically different profiles being used by the different frames, would you expect the drag deltas to be different between frames and between flow conditions? Without a doubt (e.g. the downtube profiles given, in yaw, and with legs so the onset flow angle on the downtube being more pronounced, the Trek Kamm profile seems actually quite sensible while the ridley will likely get hammered - i.e. you'd expect the relative performance of the trek to improve with respect to the ridley under a mannequin test). Same goes for all the components on the frame. This is the source of error and doesn't allow you to draw the conclusions that are being made with any certainty. This is why a mannequin test is more useful because the delta between one human and another is much smaller than no-rider to rider (i.e. this is the truer test of aero performance), though you have to account for the error in the estimation of the mannequin drag, which adds complexity - the error term here comes from the drag measurement, not deltas due to different flow conditions.
(Note, which is not to say that the Giant is not a good aero performer, you just can't derive that from this test; and back to the original question, BMC or Giant, again, the non-inclusion of the BMC should not be a factor).
It would be great to see a public-domain rider vs riderless comparison, across different frames. Because, consider this, if riderless testing gave you accurate drag deltas off a simple testing protocol, why do manufacturers use mannequins and moving legs, and why the interest in track based measurement systems bypassing all the issues with tunnel testing completely?
Tinea Pedis wrote:
Again, with an eye to keeping it reasonable on the budget a mag has for this testing in the first place.
I absolutely respect this, but I think there needs to be a clear understanding of the value and the meaning of testing on both the consumer and the commissioning side of the equation. Presenting results without debate/discussion is not useful to anyone.
Tinea Pedis wrote:
let alone lay members of the public
I write for a bike mag.
With respect, the subject matter is aerodynamics, not journalism!