I ride solo because I don't trust myself with others ..seriously I've been riding for a long time but almost always alone so while I'm familiar with my bike (at least my old steel, the new one is still a work in progress) I am not comfortable riding surrounded by other cyclists. If I get into a pack I will either slow and let them go or speed up and get ahead of them. 1 or 2 riders isnt too bad but more than 3 or 4 and I get a bit nervous. Further I am comfortable setting my own pace and not someone elses. I know I should change but that is going to take some time. It would probably useful to join a club but right now I don't have the time to do so