If you are pinching a wider tire on the same narrow rim you can end up with considerably LESS contact than the design size. Very seldom does a wider tire equate to a larger contact patch. There used to be a web site that had a guy's illustration of this by mounting different tires on the same bike and wheel, and rolling them over white paper in the upright, 15 degree, and 25 degree angles with 1 g loading (just bike weight) to show how different the contact patch can be, and the majority of the time, bias ply wider tires resulted in LESS contact at the higher lean angles than the stock size. As much as I fight with them on a regular basis, engineers do actually know and understand a thing or two.