If yoy have trained for it, DO THE 100-miler! The only time I ride with my husband is if we are touring, and he is carrying more weight to equalize our speeds. I prefer to 'ride within myself' going at the pace I feel like going (which isn't necesarially slow, just slower than my husband's natural pace). In a large group ride there will always be folks going your pace, and only you can decide if it is more fun to join a group, or do it on your own. Also, groups reshuffle at rest stops, so nothing is permanent, and if you really feel hampered by a group you can rde with them for a while, and then just pass them. If its windy, you may be more inclined to join a paceline than if its not. I enjoy the solitude of riding with my own thoughts, as well as the interesting conversations that can come from the right people, or sometimes the wind protection of a fast paceline. Just watch for the bike handling skills of those you paceline with. As for changing the tire, just practice first, it is trivial (I should know, I changed 4 flats and mounted 3 new tires this week on 2 bikes ), and a must skill for any cyclist. C02 is easier than a pump for high pressure tires. So, practice and carry a flat kit, but the worst case scenario is that someone in a sag vehicle can help you out if you are really stuck. HAVE A GREAT TIME AND WRITE US A REPORT !