Originally Posted by zen_

Are you using a wheel speed sensor?

Again, I don't know how the Wahoo app calculates (virtual) speed. The three ways it can be calculated on an indoor trainer are wheel speed (usually used when power is not available), power alone (e.g. TrainerRoad, w/o simulated climbing or drafting), or power-to-weight (e.g. Zwift /w simulated climbs). The latter is probably closest to to real world speed (assuming you don't draft in a blob of riders or weigh 20 pounds less online), but they are are virtual numbers at the end of the day. The only number that matters for training inside is power, and heart rate to some degree to keep track of fitness and fatigue.