Originally Posted by brianogilvie

I think it's realistic, but if your 65-mile ride involved 7 hours of riding time, you might finish the 200K outside the time limit. (If it was total elapsed time, including breaks, you should be fine.) It would probably be a good idea to work on your speed.

I'd advise a combination of increasingly long, relatively slow weekend rides as you approach the event, combined with interval training to improve your power output. I did some high-intensity interval training in the winter and early spring and definitely noticed results on my longer rides. If you join a gym that has spin classes, you might give them a try.

The two books that I've found most useful are Joe Friel, The Cyclist's Training Bible, and Chris Carmichael and Jim Rutberg, The Time-Crunched Cyclist. The latter has a 12-week training plan that requires 6-7 hours per week.

Seconding antimonysarah about the tires. I'd look into relatively wide, supple tires: Panaracer Pasela 35mm tires are nice; the Grand Bois Cypres 30mm are even nicer but maybe a little skinny at your weight. Schwalbe Kojaks have a good reputation, too. Bicycle Quarterly's tests indicated that in real-world riding, tires with light, supple sidewalls outperformed more rigid ones.