How to calculate tire size?

14's are more forgiving how?

There is every size imaginable in 15" and then some.

If the aspect ratio doesn't change it's very hard to tell an inch difference in a wheel. I.e. a 28" tire on a 15" vs. a 29" tire on a 16".

15-17 look fine on a an Abody. I will agree if you exceed that it can often look out of place, but not always.

Tire and wheel style and sizing looking correct on a vehicle is very dependent on the whole package. THe best tire and wheel combos fit the over all theme of the car and also fit properly under the car, including the all important but often neglected or misguided ride height