This is utterly amazing, to see the game the even the Megadrive can't run without an extra processor running unaided on the Pico8. Simply astounding.
I noticed something odd: when I set a fastest race time on the Medium track, it lists the track record for it under the Expert track on the track select screen (I assume it would list an expert track record under the medium track on the track select too, but I can't complete the expert track).
I am playing the Windows version, so I deleted the save file from the cdata folder and tried again and it did the same thing again.
I also tried it in the browser version above and it also lists the medium track record under the expert track.