737 Improved Climb with Tailwind

[metabolix]

Mesdames et Messieurs

A recent performance lecture threw up an interesting conundrum. It was discussed that when using the Improved Climb pages of our Airport Analyses, by using the 10kt tailwind column, as opposed to the 0 wind column, this resulted in lower V-speeds (V1 and Vr. V2 seems to stay the same) for the same (or similar) weight. Removing all the arguements about reduced flex etc, the question I am asking is:

“If lower V-speeds (V1 and Vr) are acceptable with a tailwind, then why would those speeds not have been used in the 0 wind column to start with?”

Bearing in mind that the V-speeds are based on weight and airspeed over the wing, the only reason I have been able to come up with is that when there is a tailwind there may be a reduced IAS (for a given TAS), as the compression in the pitot tube may be slightly less even though the airspeed over the wing maybe the same, thereby giving an under-reading on our IAS (although not our TAS). So if the IAS is under-reading, the V-speeds may reduced accordingly (while the TAS actually remains the same). But all of this really depends on the linear relationship between tailwind and relative pitot compression and whether or not one fully cancels out the other. This is way above my level of understanding and I turn to your learned selves for guidance.

Thank you in advance