With the auto industry still trying to regain its footing in the market, many people are looking for new ways to spruce up their ride without replacing it. Rims can add an entirely new look and feel to a car, making even the oldest Oldsmobile look refreshed. Because these DIY updates require some personal knowledge on car and tire manufacturing, questions regarding size and fitting are very common. Tires and rims can be swapped and interchanged easily. Located directly on the sidewall is information regarding the rim size, as well as other important facts about your particular brand of tires, such as the type, load capacity, additional dimensions, and temperature and speed durability. In this two part series is an easy way to understand the combination of letters and numbers for typical passenger cars, using this tire size as a reference: P225/50R16 91S. First letter = Service Type P225/50R16 91S •    This information lets you know what type of car your tires are designed to equip. P-metric is the most common tire size, with cars, SUVs, vans, and light-load trucks belonging in the category. •    P = Passenger cars. •    T = Temporary spare. •    Cars that do not have a letter preceding the 3 digit segment of the tire size are typically measured in "Euro-Metrics", meaning the tires are probably made for a European passenger car. Following 3 digit segment = Section Width P225/50R16 91S •    This is the measurement in millimeters from the widest point of the outer sidewall to the widest point on the inner sidewall. Following 2 digit segment = Sidewall Aspect Ratio P225/50R16 91S •    This is the ratio of the sidewall height to section width. Sidewall heigh is measured rim to tread; according to this example, the sidewall height is 50%  of its section width. The higher the number, the taller the sidewall. The second part of the tire and rim size series will break down the rest of the tire size description.