Based on the text, explain what the marking '195/65 R15' on a car tire means.

The marking '195/65 R15' on a car tire provides several key pieces of information about the tire's dimensions and construction.

1. 195: This first number indicates the width of the tire in millimeters. In this case, the tire is 195 mm wide.

2. 65: The second number is the aspect ratio, which represents the height of the tire's sidewall as a percentage of its width. Specifically, it's calculated as $$100 \cdot \frac{H}{B}$$, where H is the height of the sidewall and B is the width of the tire. In this example, the height of the sidewall is 65% of the tire's width.

3. R: The letter 'R' indicates the tire's construction type. 'R' stands for radial construction, meaning the cords in the tire's carcass run radially across the tire.

4. 15: The final number represents the diameter of the wheel rim (disk) in inches that the tire is designed to fit. So, this tire is made for a 15-inch wheel rim.

In summary, '195/65 R15' tells us the tire's width (195 mm), the aspect ratio (65%), the construction type (radial), and the wheel diameter (15 inches).