I organize bike rides for a group of 50-plus riders. There is a wide difference is ability in the group and some people ride at 15-19 mph while others are comfortable going 10-15. To accommodate these differences, I have the group stop frequently for re-groups so that everyone feels like they're part of the ride. But I have been hearing complaints and concerns that the slower riders are feeling too much pressure to go faster and the rides are not as fun. What should I do?