Dude, what are you thinking?
In my opinion, the most important thing you can focus on is to become much more healthy than you currently seem to be. Pushing yourself to win a 12 mile race is probably not going to help you much.
If you must compete, look for other interests that will be somewhat more kind to your body, especially considering your knee, back and colitis.
Maybe consider competitive water skiing, swimming or other water sports. If you live near the ocean look to some of the surfing-type sports such as surfing, sail surfing etc.
Maybe get into dirt-bike riding or other such sports.
Maybe just do a combination of some of these sports just to enjoy them for their own sake and not to win.
Just my thoughts. Good luck with your physical situation.