I see it as this, you sign up with name, location and interests, you choose these interests off a predetermined list created by the app. Then when you are doing a sport the app will enable you to make this obvious e.g Rich, Bristol, Trials then perhaps with the use of location services like on phone maps and stuff will give an exact location or with a text function could input Lloyds.
With the interests it means say I was also a climber I could view both sports in my area and choose based on what I can see others doing, it also enables a filter too, I could look at just trials or perhaps I want to go watch BMX could see whats going on within 2 miles of my location.
Perhaps a search function with interest, location and distance from location.
The ability to "follow" people would be good too and perhaps optional in app notifications of when people are in your area or when your followed people are riding.
I think it's a great idea but relies on two things, people using it and people being friendly.