Something else I forgot to mention, whilst nowadays 'some' car players "might" be able to play CD-RW's, most can not. CD-RW's do not read as easily as CD-R's. Due to the difference in manufacture and physical qualities of the actual disk, their radiance or magnetism if you like is not as bright and more difficult for players to read. (I can't remember what it's called but I think you know roughly what I mean.)
CD-RW's are made differently so they can be re-written.

In my experience, definitely quality and brand of cd-r made a difference. Including speed type and speed burnt at. But that's a few years ago now.