In Collin's dictionary, when I search for Rad fahren, it comes up with: http://www.collinsdictionary.com/dictionary/german-english/radfahren
However, radfahren is not on http://de.wiktionary.org . They said that reforms changed the verb radfahren to Rad fahren. Then why is another famous dictionary not using that information?
Furthermore, I am being very confused about the role of the other word "Rad". Does it matter where it is in the sentence? Is it a separable prefix?
Although this answer is on the site: Spelling of noun-verb compounds , I did not feel that it specifically answers my question, nor that it confronts the issues in my question.
Thanks in advance