There's a bit of misinformation in this thread.
The profile is a PERCENTAGE of the width. Not a dimension in itself.
So for example, the sidewall of a 255 35 19 will be taller than the sidewall of a 225 35 19.
And width does vary, often by 10mm or more, by manufacturer. Not all 225s are even close to 225.
willtheyfit.com is useful, but knowing the basics is essential.