Yesterday I was out for a leisurely ride in Flanders. Most of the route was totally flat. I'm used to cycling in such terrain in Noord Holland, and typically on a ride of more than about 25k, will average 20kph. Today I did 77km at an average speed of 24.7kph. Nearly 25% faster than my usual speed. There was a tail wind, but it was ever so slight. Yr.no says 1-2m/s. So under 7kph. I've had tailwind before (rare, but it does occasionally happen), but even in a stiff breeze strong enough to move branches on trees (which today's didn't), I've not been able to manage such a speed for so long.
This is a long way of getting to the question, how much impact can be reasonably expected from a tailwind? If I typically do 20kph, how strong would the tailwind need to be to increase my speed to 25kph, without requiring more power ?
J