It doesn't matter if you have a regular passenger car , a light truck or SUV or even a sports car, having properly sized tires on your vehicle is the key to getting the best performance out of it. Poorly fitted tires will make the car harder to handle and can potential damage things like the suspension system or brakes. The easiest way to know what size tires your car takes is to look at the number on your existing tires. This works great if you bought the car new as the factory should have installed the proper tires. However, if you bought your vehicle second hand, the previous owner may have chosen tires that were a different size. You can look in the inside of the driver side door where there is a plate telling you what size your car takes. You can also check with the manufacturer to see the recommended size. You may want to ask your mechanic or take your car to a tire shop, however, if you're buying discount tires online , you will need to know what size before you start shopping. Looking at that long sequence of numbers on your current tires is going to be your best bet. The two most important numbers are the first three digit number and the second two digit number. Looking at a sequence like P195/75R14 92S, you want to note the 195 and the 14. The first number is the width, in millimeters, of the tire at the widest point. The second (14 in the example) is the rim size, in inches, that fits your vehicle. You may also want to consider the final number (92), which indicates the load index the tire can carry. This is especially important if you find yourself hauling heavier loads than the average driver . It is okay to get tires that are oversized or undersized, you just need to be very careful in your selection. Research the acceptable variations for your specific vehicle and always consider the road and weather conditions you drive in as well as the amount of weight you carry.