[audio cassette player] Are both or only one "axis" supposed to drive the tape?
(piefed.cdn.blahaj.zone)
There's no need to fix it since the tape is recorded the same way it's played.
Like a vinyl record, the grooves towards the outside of the platter are moving faster than the grooves on the inside yet it spins at a constant RPM.
One advantage of analog is that there's no constant "bitrate" that has to be maintained though faster moving analog media generally translates to higher fidelity.