Welcome.
Yamaha are pretty good at looking at industry standard specifications, then doing their own thing.
Your Tyros does MP3 recording but I cannot see at what data rate it does it, suggest you look into this, the manual does say max song size of 300KB whatever that means.
Your car stereo may well have limits to what it can playback with probably an MP3 being recorded at a specific rate in a data range of 96-320 mbps.
A workaround would be to record to a PC or Mac and then process the audio file to suit.
I ripped my CD’s to MP3 at a data rate of 320mbps and they sound pretty good at that, not as good as a WAV or AIFF but it is as good as you get with an MP3.