[TireFitLab](https://tirefitlab.com/) › [Tire & wheel reference guides](https://tirefitlab.com/learn/) › Tire aspect ratio guide # Tire aspect ratio guide ## What is the tire aspect ratio? The aspect ratio (e.g. 55 in 205/55R16) is the sidewall height expressed as a percentage of the section width. 55 means the sidewall is 55% of 205mm = 112.75mm tall. A lower aspect ratio = shorter, stiffer sidewall, sportier handling. A higher ratio = taller sidewall, more cushioning, common on SUVs and vans. ## Decode a tire size Type the main sidewall size string to see the width, profile and sidewall math. Tire size ### Section width 225 mm ### Aspect ratio 45% ### Sidewall height 101.3 mm ### Overall diameter 634.3 mm Reference-table value only. Always match your vehicle placard and tire sidewall markings. ## Worked examples Metric and flotation markings look different, but the table is calculated from the same nominal diameter, width and rim-size rules. | Size | Overall diameter | Section width | Sidewall | Circumference | | --- | --- | --- | --- | --- | | 225/45R17 | 24.97 in / 634 mm | 8.86 in / 225 mm | 3.99 in / 101.3 mm | 78.45 in / 1993 mm | | 285/75R16 | 32.83 in / 834 mm | 11.22 in / 285 mm | 8.42 in / 213.8 mm | 103.14 in / 2620 mm | | 33x12.50R15 | 33.00 in / 838 mm | 12.50 in / 318 mm | 9.00 in / 228.6 mm | 103.67 in / 2633 mm | **What to do with it:** Round marketing sizes can hide several millimetres of difference. ## What aspect ratio means The aspect ratio is the sidewall height expressed as a percentage of the tire section width. In 225/45R18, the 45 means the sidewall height is 45% of 225 mm. ## How to calculate sidewall height **Sidewall height = section width × aspect ratio ÷ 100**. For example, 225 × 45 ÷ 100 = 101.25 mm of sidewall height. Changing the aspect ratio changes ride comfort, rim protection, visual stance, and overall tire diameter. ## What changes when the profile changes - **Lower profile** — shorter sidewall, sharper steering feel, firmer ride, less rim protection. - **Higher profile** — taller sidewall, more cushioning, more rim protection, usually slower steering response. - **Overall diameter** — width and aspect ratio work together; always compare the full tire diameter before changing sizes. ## Popular aspect ratios - [/35 series](https://tirefitlab.com/learn/aspect-ratio/35/) - [/40 series](https://tirefitlab.com/learn/aspect-ratio/40/) - [/45 series](https://tirefitlab.com/learn/aspect-ratio/45/) - [/50 series](https://tirefitlab.com/learn/aspect-ratio/50/) - [/55 series](https://tirefitlab.com/learn/aspect-ratio/55/) - [/60 series](https://tirefitlab.com/learn/aspect-ratio/60/) - [/65 series](https://tirefitlab.com/learn/aspect-ratio/65/) - [/70 series](https://tirefitlab.com/learn/aspect-ratio/70/) ## Related guides - [Learn hub](https://tirefitlab.com/learn/) - [How to read tire size](https://tirefitlab.com/learn/how-to-read-tire-size/) - [Section width](https://tirefitlab.com/learn/section-width/) Seasonal check ## Planning a long summer drive? Use the budget and running-cost tools before a trip, especially if the current tires are worn or the replacement size changes diameter. [Estimate tire budget](https://tirefitlab.com/tire-budget-calculator/) ## More in this topic: Size validation Decode markings, compare sizes, and understand diameter, load and speed changes. - [**How to read a tire size** How to read a tire size: decode every number and letter in P205/55R16 91V — width, aspect ratio, rim diameter, load index, speed rating.](https://tirefitlab.com/learn/how-to-read-tire-size/) - [**Tire type guide — P, LT, metric, radial & flotation** What do the letters in a tire size mean? P, LT, metric, radial (R) and flotation tire types explained.](https://tirefitlab.com/learn/tire-types/) - [**Tire sidewall markings decoder** Complete guide to every marking on a tire sidewall: size string, construction code, load index, speed rating, DOT date, M+S, 3PMSF snowflake, UTQG, max pressure, country of manufacture, and brand-specific symbols.](https://tirefitlab.com/learn/tyre-sidewall-markings/) - [**Tire load index chart** Use the tire load index chart to convert ratings 60–130 into kg and lb, then verify the vehicle placard and axle-load requirements.](https://tirefitlab.com/learn/load-index/) ### Useful tools [Tire size converter (mm ↔ inches)](https://tirefitlab.com/tire-size-converter/)[Tire size calculator](https://tirefitlab.com/tire-size-calculator/) ### Technical check 2026-06-28 ### Content updated 2026-06-21 What changed - Checked generated routes, metadata, sitemap inclusion and localized page rendering. [Methodology](https://tirefitlab.com/methodology/)