The aspect ratio, represented by the second number in your tyre size (e.g., '55' in 205/55 R16), indicates the height of the tyre's sidewall as a percentage of its width. This ratio affects the tyre's handling, ride comfort, and overall performance. A lower aspect ratio generally means better handling and a sportier feel, while a higher aspect ratio can offer a smoother ride. Choosing the correct aspect ratio is essential for maintaining your vehicle’s handling characteristics and comfort.