What I was thinking of is that there's no limit on our minimum speed, other than zero. The stronger the wind, the slower we go.

For many of us, there is a limit on our maximum speed -- safety in turns and on descents, road conditions, etc.

So while a very strong headwind will slow us to its full potential, the same wind may not benefit us proportionately coming from behind -- not because of the math, but because of the realities of cycling.

You may have a descent you normally take at, say, 40mph. A 40mph headwind might slow you to 20mph. But you're probably not going to use a 40mph tailwind to do the descent at 60mph, because that's faster than you feel safe going.

Riding in the city, I still have to slow down at intersections and stop at red lights, no matter how strong the tail wind.

That's why on windy days I find my average speeds are generally noticeably lower, even if there was a tailwind one way.

RichC