Keep in mind, too, that some groups ride are in a paceline formation. In a paceline, you typically ride very closely behind the rider in front of you, either in a long single file line or, if conditions allows, two abreast. Each person takes a turn "pulling" at the front of the line for a short period and then rotates to the end of the line. In a paceline, it's easily easier to go faster than you would otherwise ride on your own. But also keep in mind that it takes some pretty good bike handling skills to ride in a paceline. If you're a new rider, you might stick to rides where people simply ride together in a loose group. It'll get you used to being around other cyclists without some of the dangers that pacelines pose. That's how I started at first. I eventually progressed to paceline riding, which can be a lot of fun (and a little scary).