Yes, there are other factors such as the tire carcass stiffness and the tread. But the overriding factor is still the internal pressure, especially so when considering two tires that are identical other than the aspect ratio. Again, a common belief is that changing a tire to a higher aspect ratio changes the amount of rubber in contact with the road is just not correct.
A toy balloon would act more like a perfect vessel than a vehicle tire regarding the pressure / area function. For example, all the stiffness in a balloon comes from internal pressure only- bring that pressure to zero and the balloon really will lay flat. The same is not true for a tire of course, even without pressure there is enough stiffness in a tire to hold it upright and hold its shape. So yes, there are other factors and they must all be considered; it is certainly not universally simple and true that contact patch area is a function of internal pressure alone but it is the predominant factor.
As far as tire shape goes, again that will be overridden by the pressure / area relationship. If the shape of the tire is brought more toward a triangle in an effort to increase patch area, and the same internal pressure is used, the actual result will be that the patch is wider but shorter (in the direction the motorcycle travels). Even a clever designer cannot outsmart or outrun physics.
One obvious example of other forces would be the way wrinkle- wall tires act when used in drag racing. The contact area is a function of the internal pressure (which is extremely low to use a lot of contact patch area) at first but then centripetal force must be factored in. With the vehicle sitting there the tires appear almost flat but once the tire is spun up to high speed, it becomes much more round and much larger in diameter as well as narrower. The back end of the vehicle is raised up quite a bit- it is not a subtle effect. I do not know but suspect that the contact patch area changes with this great increase in centripetal force. Of course such things are hard to duplicate on street vehicles, not to mention that fantastic acceleration is never used when a motorcycle is leaned well over in a curve so it is irrelevant.
The short version is this example: if you replace a Michelin PR3 190/50- 17 with a Michelin PR3 190/55- 17 and like the taller tire better, I betcha' it ain't 'cause of the idea that the contact area changed (assuming the same tire pressure is used!).
Brian
I sorta agree here but you have use tire of same carcass construction for that statement to be true..
190/50 as opposed to 190/55 would be different construction no??
It has a different shape...
I think a tire with different profile could put more rubber on the road at certain lean angles even using same psi