If you can do 25 miles with no problem you can do 50 with no problem! You are fighting a mental battle, like a previous poster suggested, break it up into two 25 mile rides with a lunch stop in the middle. You can do it and you will feel so good afterwards.

I always find that my biggest challenges are mental not physical and that I have to play mental games with myself when I am having a rough time. A few years ago I did Pedal the Peaks out west a couple times which is a week of climbing, all.day.long., about 600 miles for the week. I would just have to say, ok just make to that tree and then you can stop, then I would make it to the tree and I would say ok make it to the pole and then you can stop, I would do that for hours. Sounds fun huh? It was the best actually.

You can do it, sending riding Karma your way!