MP3 recording quality and file size

I have a Panasonic car MP3 player, (CQ RDP 472N). It is quite old now, but still plays pretty much anything I throw at it, even after the CDs have been on the floor of the car. I am trying to optimise the number of books / tracks that I can get onto a single MP3 CD. Clearly I want to record speech at the lowest rate which will still play. In my case this turns out to be 56 Kbs. As an exercise I recorded the same 2 min track Several times. Simple Minds, Street fighting years, track 11 – “when Spirits Rise” was chosen because the track is 2 minutes long.  I recorded this using Music match, which tags the tracks with simple ID3v1 and ID3v2 tags, not including any album art.

MP3 quality	Size (bytes)	Mbytes/min	per CD	full CDs	RDP 472N
16 kbs	250K	124K	89 hours	66
32 kbs	487K	241K
56 kbs	841K	417K	26 hours	19	plays
64 kbs  FM	476K	960K	22 hours	16	plays
96 kbs  nr CD	1.4M	700K	15 hours	11	plays
128 kbs CD	1.9M	950K	700 min	9	plays
192 kbs	2.8M	1.4M	460 min	6	plays
256 kbs	3.8M	1.9M			plays
320 kbs	4.7M	2.35M	276 min	3	plays
Nokia Phone		470K	25 hours