Measuring a ST trailer tire can seem complicated, but it isn't. You have three measurements to follow...first determine the appropriate sized trailer tire and the width of the tire, measure the diameter of the rim, and height of the tire measure from the top of the tire. Make sure all measurements are correct to ensure any weight carried or grounds traveled on will be supported by your tires. Metric and numeric plus alpha numeric are standard sidewall marking used to describe the section and width ratio, and inner structure of your tire.
To accomplish correct measurements lay the tire flat on its side then measure from the ground up. This is to make sure you get the right measurements. These measurements should correspond with the first value listed on the metric and numeric label. Make sure to only follow your numeric, and metric values these are most important for achieving correct measurements.
After you have measured and determined that you have the correct tire make sure to check your air pressure in the tire. The air pressure dependents on the weight of your fully loaded vehicle anything above or below the correct pressure can hinder the performance of your tires.