Originally Posted by
rex615
There are some rough assumptions used for gearing calculations but that won't be accurate enough for your requirements.
Tire size can vary a lot with tire brand and many tires don't actually measure true to their nominal size.
Wheel width with have an effect on tire shape, same tire on a wider rim will be wider and have less height.
If you are mounting the larger tire on the same rim it may be a little taller than expected because the tire may be rounder in cross section. Unfortunately there is no easy calculation because the variables.
In many cases the height limitation is rear brake or the brake bridge as you point out and this varies too.
If you are trying to mount a specific tire on a specific frame, there is a very good chance someone here can tell you if it will work.
I've always imagined tire sizing as a circle that would expand concentrically (more or less) on the OD of the rim according to the size (width) of the tire. That said, theoretically, a 1mm increase in width would increase the diameter by approximately 2-3mm. It's probably way more complicated than that.