What does tyre aspect ratio mean?

In the tyre size 175/65 R14 82T, the number 65 is the aspect ratio. It means the nominal sidewall height is 65% of the tyre’s 175 mm nominal section width.

How do you calculate the sidewall height?

Multiply the nominal section width by the aspect ratio as a decimal:

175 mm × 0.65 = 113.75 mm

So the calculated nominal sidewall height in this example is approximately 113.75 mm. This is a useful calculation for understanding tyre dimensions, although actual mounted dimensions can vary slightly between tyre designs and approved rim widths.

Breaking down 175/65 R14 82T

• 175 – nominal tyre section width in millimetres.
• 65 – aspect ratio.
• R – radial construction.
• 14 – nominal wheel/rim diameter in inches.
• 82 – load index.
• T – speed symbol.

Does a lower aspect ratio mean a shorter sidewall?

For two tyres with the same section width, a lower aspect-ratio number means a shorter nominal sidewall. However, the percentage is always relative to the tyre width, so the aspect-ratio number should not be considered on its own.

Can I change the aspect ratio?

Do not select a replacement tyre from the aspect ratio alone. The complete tyre size, load rating, speed rating, wheel dimensions and vehicle manufacturer’s requirements all need to be considered. An unsuitable overall diameter or specification can affect clearance, gearing, speedometer readings and vehicle behaviour.

For more detail, see how to read a tyre size from the sidewall.