I go through the same thing everywhere I go all my life long. It sucks. but sometimes it's not what you're doing or not doing; sometimes they really are stuck up bitches. Some groups are just very cliquey. We're not the only ones who have issues, after all!
I think you've done all you can to let them know you want to be more included than you have been. Maybe you can bring someone else along with you on these group rides? Sounds like the group dynamic is changing, if you were there first and then these other people came along. I've had that happen too, I was once on a frisbee team that was a lot of fun even for a non athletic marginally socialized outcast like me; then the manager moved away and her replacement was a total bitch who only wanted certain people on her team and no one else was welcome anymore.
If you watch groups of people from the outside you can see who's connecting and who isn't. There's some people who just cannot connect with others and I know I'm one of them. Maybe you are too. I can't pin down what it is but it's like we're in a parallel universe that's a half step off of the other one everyone else is in. I've been job hunting for a year now and I'm finding that it's the ultimate, high-stakes popularity contest. None of my qualifications or skills seem to count for anything. They just plain don't like ME for some reason. I get lots of interviews, but no offers.
Sometimes it's acting too aloof, and sometimes it's acting not aloof enough, and too desperate or pushy or clingy. And sometimes it's the other people who have the problem.