Unless something is wrong here:
9 in = 228.6 millimetres
so 225's on a 9in would give approx 3.6mm of stretch.
AKA nothing noticeable.
The tread of the tyre is roughly the same of width of the rim, so the sidewalls will be more or less right angled.
9.5 in = 241.3 millimetres
235's on a 9.5 would give 6.3mm stretch, which i believe would just start to get noticeable.
If i've got it wrong let me know.