Tire sizing is much more than what will fit a rim. You can have cupping and bowing for one and it can still be mounted. It can rub the body/suspension also.
In general you want to say within 3% of your original diameter.
This is the basis of the Plus 0, Plus 1, Plus 2, Plus 3 sizing
the way you can get a general idea is (if a spec chart isn't avaliable):
Tire Width*aspect ratio*2+wheel size = tire diameter
215/25.4 = (millimeters to inches) = 8.464567 * 0.55 = 4.655512 * 2 + 16 = 25.31102
225/25.4 = 8.858268 * 0.50 = 4.429134 *2 + 16 = 24.85827
25.31102/24.85827 = 1.018213 this is less than a 3% difference so you will be ok.
the difference is how much your speedometer (and odometer) will be off.
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