Lets Ride Bikes is a Euphemism meaning lets have an online conversation.
Thus the act of "Riding Bikes" with some one. Refers to having an online conversation with them. And applies to conversations had on a website or over a chat system such as Msn or Skype.
By asking some one to ride bikes with you or by saying "Lets Ride Bikes" you are inviting them to talk with you over the computer, online.