All depends of the subjectiveness of the ride. I went to calculate mine on MB and found that my overall avg. was 15.2 mph on 21 rides. Now these rides all include hills and some mountains we have climbed one of which we climbed twice that is a 16 mile climb..............yes, 16 mile climb. Varying grades also! Some very steep that slow you to an almost 3-5 mph rate.

I think on overall rolling terrain and flats I would probably be around 19 mph avg. but that is not pushing it, more like a constant cadence with minor to medium effort.