What the others said. My longest ride to date was RAIN (ride across indiana) which was 158 miles in a day. I think it took me 9.5 hours total, that included breaks. I start my insanity....er brevet series on saturday with a 200k. It's kinda warped that I think to myself "well that'll be easy." But you do get used to the hours in the saddle, and you're right most of it it mental. When bits start to hurt you have to will yourself past the pain and keep going. I did 91 miles the other day and was cursing because I didn't eat enough and didn't use my BUTT'R. So I was hurting. But if you do a few basic things to keep that pain away, you can go a lot further than you'd ever expect.