Riding with a group - average speed?

[velo]

Thanks for all of the replies and helping me think this through a little more. I probably am overthinking it, but that is my personality to do so. I wasn't able to reach the contact for the ride... not sure if he's moved away or what, but my email bounced and the listed person was not at the number I called. I do know another fellow who rides with the group and when I've asked him, he just says, "Yeah, it's a fast ride." I do not know him well, and he is difficult to talk to.

It has been some years, but I figure pacelining and group riding will come back pretty quickly. Racing (especially crits, which is what I raced) is different that group non-competitive pacelining. However, I trained with a team for a few seasons, which involved a lot of friendly close riding. Indy, your suggestions make a lot of sense... just hanging back and seeing may not be a bad idea. However, the season is nearly at a close, so I could wait until next year, but it was kind of a goal I had. I had said that when I could consistently have a rolling average of 18, I'd try the group ride. Then I started second guessing myself and coming up with reasons to not do it. I'm not great on the few "hills" we have around here (less than 5% grade and very, very short) because I still have about 20lbs. to lose and on the flats, no wind, I can maintain 20-21*, in my drops, for miles, but not much more than that. I FEEL like I could be ready and would like to challenge myself in this way, but not sure. Thanks again for all of the words of advice and thoughts. You gals are great for these kinds of things. I appreciate it.
*ETA - looking at my logs, I'd say this is only for my strongest days. I can't say that's normal. I do take note of "look down" speeds in flats, and I'd say they are more consistently in the 18's and 19's, depending on wind. These would be rides 30 miles or less, too.