Originally Posted by supcom
You obviously have the additional handicap of a singlespeed. Out of curiosity, how hilly is it where you live? My experience is that brevet routes do not shy away from hills so you better include some in your training.
Both of the New England brevet series (Boston and the Berkshires) use "3000 ft. of climbing per 100km" as their rough rule of thumb for route planning. Boston-Montreal-Boston has about 30,000 feet of climbing (or roughly 2500 ft. per 100km). A few of the other supers (Gold Rush, VanIsle) have similar amounts, and even the "flatter" rides like Last Chance and PBP swap climbing for vicious headwinds. So it's worth training with those amounts in mind.