It has only 4 wheels. Four. It can't levitate. Even real 0-4-0's rode roughly. Our model tolerances exaggerate the sight. If you want more smooth, you need more wheels. Early "lightweight" actual passenger cars on 4-wheel trucks rode less smoothly than the heavyweights with 6-wheel trucks that they replaced.
One problem with even an 0-6-0 in our 3RO world is that the center blind driver only intermittently actually touches the rail, so the 0-6-0 is a bit of an 0-4-0, itself.