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.
- 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
Related guides
Seasonal check
Winter tire rules coming up?
Check tread depth, markings and local winter requirements before the first cold spell instead of waiting for the appointment rush.