Joe,
I rode RAGBRAI in 2010. I did exactly one training ride of just over 50 miles, though I was a regular year-round, all-weather commuter at the time. Even the longest day—nominally 89 miles but just over 100 once we found our camp site—was tolerable. As with Brent's experience, I had almost perfect weather—never in the 90s, and only one day with rain, for which I was well-equipped. There was one night of ferocious thunderstorms and gale-force winds, but my tent held and our group had secured a camp site on higher ground so we had no flooding. I rode with a local cycling group that hired a truck and a crew of college kids who ferried our tents and gear from one overnight town to the next. They also secured the camp site for each night, and set up our own outdoor shower booths in which we could, if we didn't want to stand in line for the pay showers, hang up our sun-shower bags and get clean. Some of the group preferred the pay showers; I never visited them and so cannot speak to that part of the experience.
If you do the ride, and aren't the partying type, I suggest rising every morning about 5:15 or 5:30 to be on the road by 6:00. Once you're out of each overnight town, vendors will have food trucks of various kinds set up along the route (I had excellent espresso every morning), and the first pass-through town of the day will often have great breakfast service. Plan to buy your meals in the towns. Being on the RAGBRAI route may be the biggest economic boost some of the smaller towns have for years, and the folks go all-out to be welcoming and offer good and filling food.
You may, of course, choose to ride RAGBRAI as a self-contained tour, carrying your tent, gear, food, etc. on your bike. Know that you will be good-naturedly hazed as a "bagger." Either way, because this would be your first RAGBRAI, you will also be hazed as a "virgin."
I took my time, aiming for an average speed of 10 mph, including rest and meals. That is, if the day was 70 miles, I aimed to finish the leg in 7 hours. I enjoy conversation as I ride, so I generally rode at least some part of each day with a companion, either from my group or someone I met on the road.
I lived in Iowa at the time, and had done so for ten years before I rode RAGBRAI. For most of those ten years I was convinced that riding across Iowa during the hottest time of the year was lunacy. Indeed it may be, and have been, but I learned in the process why some people ride it year after year.
What bike will you ride?
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Bob