Tyre Geometry — Definition of Aspect Ratio (Expressed as a Percentage) In tyre specifications, the aspect ratio is given in percent. Precisely, it is the ratio of which two dimensions?

Introduction / Context:
Tyre markings like 205/55 R16 encode width, aspect ratio, and rim diameter. Understanding what aspect ratio means is vital for handling, comfort, speedometer calibration, and wheel well clearance decisions.

Given Data / Assumptions:

• Aspect ratio is reported as a percentage in standard tyre notation.
• Section width is the nominal width of the inflated tyre (in mm) excluding protective ribs.
• Section height (also called sidewall height) is from bead seat to tread.

Concept / Approach:
Aspect ratio (%) = (section height / section width) * 100. For a 205/55 R16 tyre, the sidewall is 0.55 * 205 ≈ 113 mm. A lower aspect ratio means a shorter sidewall, typically improving steering response but reducing ride comfort and rim protection.

Step-by-Step Solution:
Identify dimensions: height (H) and width (W).Definition: AR = (H / W) * 100.Match to options: section height to section width.

Verification / Alternative check:
Cross-check any tyre marked XXX/YY: YY is the aspect ratio; computing H = W * YY/100 validates the definition.

Why Other Options Are Wrong:
Width/height is the inverse of the standard definition.Ratios involving wheel diameter are unrelated to aspect ratio in tyre coding.

Common Pitfalls:
Confusing tread width with section width; they differ.Assuming aspect ratio is a fixed size rather than a proportion tied to the chosen width.

Final Answer:
section height to section width