When I ride with friends, I prefer to enjoy the experience of riding separately from being with friends at stops and before/after the route.
If a person is riding off the trail or road repeatedly, they either have a medical issue needing attention or are too careless to be trusted. The next incident might involve other vehicles. In any case, how to convey that tactfully may be too difficult to broach. Please try not to be a part of the next coming inattentive mistake.
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Vintage, modern, e-road. It is a big cycling universe.