My uncle and I ride together occasionally. He usually hangs way back, sometimes I can't hardly see his headlight. The biggest problem is in town, where he consistently misses my light, and I have to pull over and wait for him. I only ride with him on the days where I feel realllly patient. In contrast, I thought the group leaders on the midwest rally did a great job with keeping everybody together. Bottom line, some people just don't do buddy rides very well.
