Originally Posted by
zen_
I have not used the Wahoo app, but the virtual speed on most apps is based on your power, or power to weight ratio (w/kg).
The only things that actually changes when shifting gears in ERG mode since the power is theoretically, and in practice mostly the same is peddling dynamics (it's worth the 7 minutes to watch this video).
https://www.youtube.com/watch?v=uHUOhmG04M8
I will put it this way: When I look at my Wahoo APP while riding in ERG Mode, and switch the gear ratio, my speed changes, but power remains the same.