Just so everyone understands:
There is no regulation that requires tire manufacturers to produce tires that match the size indicated on the sidewall. In other words, different tire manufacturers can produce tires of different diameters even if the size is the same. Further, even within a given tire manufacturer, tire diameters can be quite different. (Don't ask how I know.)
And as I was quoted above, vehicles tend to rotate around odd tires in emergency situations - and the more odd the tire is, the more this tendency. The problem here is that you won't know until you are in the situation - and then it is too late! You can't test for this unless you destroy that set of tires.
So the question is, how big of a risk are you willing to take?