To add to what Roadraven said, in case this is your question, but in event rides you are not riding in a big group. At least for most event rides.

There is a start time and a time when the routes close. You show up early to pick up your registration packets pin the number on your jersey, look at the map for your route and so on. Then you take off. There is no big line up at a starting line (for most of these events). Cyclists start their routes when it suits them to do so, therefore cyclists are spread out over the miles. You can pedal for miles and not see another cyclist. You might have small packs pass you, people who got together to do the ride who belong to a club together or who are just cycling buddies. Or you might pass a cyclist now and then. You meet some cyclists at the rest stops. And then there is always one turn in the route at each event where a lot of cyclists get confused, stop, congregrate and debate in which direction to go. Follow the marks on the pavement and ignore the idiots.

My point is there is no reason to train in groups to do an event ride. Pick the route for the number of miles that is a bit more than you are used to doing, so that you have a challenge. Always stop at the rest stops, and always refill your water bottles with whatever liquid you choose, and always eat something with salt and carbs in it. Don't ever pass a rest stop. If you think the numbers on your bike computer are important, then focus on your trip time, not your total time, because time at the rest stop is important to refuel the body so as to prevent low blood sugar, dehydration and electrolyte shortages.

Also, two critical key words in the text descriptions of the routes are "very challenging." If you see those two words, it really means long super steep hills with a high grade and it sometimes means miles of those super steep hills.

Darcy