All of my rides of 100 miles or more have, so far, been organized centuries. I sometimes ride with a group of people, sometimes with one other person and sometimes by myself. Sometimes I'll start a ride alone and along the way I'll fall in with one or more riders going my speed, maybe for a while, maybe for the duration. I have also started rides with a group and either dropped off the back or broken away off the front when their speed didn't suit me at the time.

I have done several solo rides of 70 to 80 miles and will likely stretch that out to a century soon. I wouldn't be surprised if my first solo century turns out to be a mixture of dirt roads and paved roads on my monstercross bike. That is when I get the most adventurous on rides these days.