Its tricky, and responsibilities are for all of us not just those trying to lead rides. Leaving 3 behind no big deal, 2 likewise, but 1 is to be avoided without mutual agreement and consideration in my view. I say consideration cos the one being left behind may say go on I'll be fine. But probably they will not be thinking straight if tired or they may be embarrassed. Ideally of course we all stay in our group and this generally seems to be the case for club runs split by pacers and amblers. The question is why does this problem only seem to arise for reliability rides or test rides, and what can be done about it, without spoiling anyone's fun