30-odd mile loop with 300m of rolling ascent (mixed units thanks to garmin settings) on Monday morning, on my 11kg Saracen Hack with 35mm slicks, averaged 19.1 mph. My Edge 500 records 5 mile “laps” and the 15 miles out into a headwind (and warming up) were all 17.X, and the 15 miles back were 21.X.
Averaged 18.5 mph over my 30-odd mile dedicated “climbing loop” (600m of mostly 10%+ gradient climbs) on the same bike and felt it the day after.
Normally average 20.something mph on the summer bike (7.5kg, 23mm slicks) on solo rides up to 50 miles in the summer. Not in a club and only rarely ride on road with mates or on sportives, and not on Strava so never had anything to compare to.