Managed to complete my first 20 miler today, done quite a few 15s but felt that 20 was a significant increase. However... this ride took 1.5 hrs at an average speed of 13.46, when I got home, my legs were shot. I certainly felt like I put the effort in! I ride a relatively heavy cyclocross bike and live in the south Wales valleys, so have a lot of hills to tackle. I know you shouldn't compare, but reading through other posts, people sniff at 20 milers, especially at such a slow pace, but I can't imagine that I can go much harder / faster.