The ride went pretty good and I found that an easy 25kmh is possible with my HR around 115-120.
But I had a guy pass me and stop three times. I think he was doing it just to see if he could catch me again and again. Other than that I didn't mind the slow ride at all and I think I will do two of these a week.
And my HRM said I was burning way more calories than fat. Usually it reads between 15-25% but last night it was much higher. I think 75-80% if I remember it right.