terrymorse 

Considering the uncertanties involved, nobody should think that the speeds estimated by a stationary bike are likely to match an outdoor ride.

But who cares? For workout purposes, speed makes no difference at all.

What matters is power versus time, and if the bike's power meter is calibrated, that should be accurate.

With today's rain and gale force wind advisory, I'll be doing a Zwift indoor ride today, and I won't even look at the distance or average speed.

[edited for tone]