If you're not sure what aspect ratio is, it's simply the width of your car's tires divided by the height. To figure out the aspect ratio of your car, you'll first need to know the width of your tires. You can typically find this information on the side of your tire or in your car's owner's manual. Once you have the width, simply divide it by the height to get the aspect ratio. For example, if your tires are 8 inches wide and 2 inches tall, then your aspect ratio would be 4 (8 divided by 2).