I used to think people were making up their average moving speeds until Strava came out and I discovered I truly am really slow. Slow folks realize when they are holding people back. When I'm in a fastish group ride, I announce that it is OK to drop me, although nobody seems to need permission.

Right now I found a mellow group who are slower than I am, and I'm never sure how I'm going to ride on any given outing. Occasionally I'll charge ahead and try to catch the "fast guys", which means I end up going solo. Too fast for the slow folk, too slow for the fast guys.

Oh well.