Metric sizing is more common these days than floatation sizing and, like the rest of the metric system, can seem a bit foreign. In this example, “295” is the section width, in millimeters. The larger the number, the wider the tire. “70” is what is called the aspect ratio, which means that the sidewall is 70 percent of the section width (70 percent of 295 mm is the sidewall height). A higher aspect ratio results in a taller sidewall, but also a wider section width with the same aspect ratio also results in a physically taller sidewall. After all that metric math, “18” is the rim diameter in inches.