The profile of a tire is based on the width and height of a cross section of the tire as shown in the following illustration. The profile is determined by an aspect ratio. This is equal to the section height divided by the section width. The ratio is given as a percentage. The lower the aspect ratio number - for example, 60 or 50 - the wider the tire. Using the above example, a tire with a section height of 7 inches and a section width of 10 inches has an aspect ratio of 70% (7/10 = 0.70 or 70%). This means the section height is 70% of the section width. Tires with the same aspect ratio are often described as being in the same series. Tires with a 70 aspect ratio are called '70 series' tires.
The load that a tire will safely carry depends on its size, its load range, and its inflation pressure. Regardless of brand, all tires of the same size and load range are rated to carry the same load at any given inflation pressure.
Tire size is one factor that determines the amount of load it can carry. The size and load rating of the tire are often given together on the sidewall.
The combination U.S. and metric system tire designation specifies the tire size and load rating in metric units and the rim size in inches. An example of a combination tire size designation is P 185/80 R 13. The letter P indicates the tire use appropriate for passenger car applications, 185 is the section width in millimeters, 80 is the aspect ratio, R indicates radial ply construction, and 13 is the wheel rim diameter stated in inches.
So. the design of your tire is matter the area that touch the road.
My experience tell me that;
ie. Michelin Certis and Michelin Vivacy when they are the same size, I feel that the touching area of Vivacy is greater than Certis (you can notice by yourselves). I am also never actually measure the size but I used to use both model.