As noted above, there's a difference in tyre wall depth between a 225 45 and 235 45 (4.6mm). I could be wrong but I'm assuming if you fit a 225 45 tyre to a 7.5" wheel, then the tyre wall depth would effectively be less again than if a 225 45 was fit to a 7" wheel, as the beads of the tyre are pulled a half inch further apart?

I think a 225 55 would be too much but a 225 50 gives a tyre wall depth about 7mm more than a 235 45. And if I'm right, then on a 7.5" wheel, how much farther would the wall depth be reduced?