I'm planning to do my first ever 200 km brevet in a few weeks, and have been training for it based on helpful tips I've read here and elsewhere. I'm not too worried about the first one; I'm pretty confident that I'll be able to finish without too much difficulty. What I'm more curious about is how long-distance riders train between long distance rides. For example, how long can you go between 200 km rides without doing a 60%-75% distance training ride in between? Or, if you've already done a 200 km brevet, what kind of training do you do before a 300 km (or greater) brevet?
The reason I ask is that, while I have enough time to train these days, come gardening season (end of May in my city), my wife and I will be competing for hobby time while the other looks after our toddler. I'd like to do more than one long distance ride this year, but I'm wondering how quickly your endurance regresses in the absence of ongoing training. Certainly it will be an option for me to go booting around the MUTs pulling the kid in a trailer, but I'm not about to take her on a 4-hour/80 km rip on a highway.
I should mention that I also cycle commute to work, about 15 km each way (up to 150 km/week if I ride every day). That'll help keep my legs and lungs limbered up, but it seems to me that commuting is a much different animal than a long distance ride.