Kickr bike V2 + Roam 3 virtual route, wrong speed

Equipment
1

Hi, I did a virtal route and used my Roam 3. I noticed downhill on 5-6% it shows 25-26 km/h. Pushing 500 watt for a short burst I got 34 km/h. The speed calculation is clearly wrong.

I took my Garmin Edge 840 and selected the same virtal route. Everything was pretty as expected. 5-6% downhill and speed 45 km/h. Also on the flat and uphill is as I experience it outside.

I searched the net and it seems Wahoo is “just like that”. Or is there a solution to this?

Indoor is of course most used to power workouts but sometimes it is just nice to check out routes and if they are ok to ride. Like now it is +10 min slower on a 23km distance at approximate the same avarage watt. Not that fun … I thought about selling the Garmin because the Wahoo outperforms it on all other usage in my opinion.

2

My experience, only with KICKR Bike V1 and Garmin EDGE 840 for last couple years, and was 830 before for maybe a year, is that I pretty much NEVER get fair treatment on the downhills, so the rides are always harder to match the speeds I would do outdoors. That’s been pretty consistently stated by many others also as far as their experiences.
I think uphills are also slightly tougher indoors, but not so much as downhills. It seems downhills are just MUCH SLOWER to allow you to pick up speed, and MUCH FASTER to slow you down as you roll onto flats or reduced grades.

I can’t explain or comment as to why the Roam would be worse, but maybe others can.