Hmm, I just heard this last night from a friend who read it in a book or a magazine (not sure if its a reputable source). The idea is that if you add up your weekly mileage, that's the number of miles you should be able to do in one ride. From my perspective, I might be able to complete the ride, but I don't think I'd be very comfortable for about the last third of it. Anyone else heard of this? Good luck! Let us know how it goes.