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What is aspect ratio on a tyre?

Analysing tyre aspect ratio

The aspect ratio is an important number in tyre size and will affect the way a car rides and handles.

Analysis

The aspect ratio is the second number in the tyre size. It shows the height of the sidewall of the tyre as a percentage of the width of the tyre. For example, in 205/55 R16, the aspect ratio is 55. This means that the sidewall height is 55 percent of the 205mm width, which is 113 mm.

Effect on the drive

Lower aspect ratio (e.g. 35 or 40)	Higher aspect ratio (e.g. 60 or 65)
Shorter, stiffer sidewall	Taller, more flexible sidewall
Sharper steering response	More cushioned and comfortable ride
Better cornering grip and precision	Better absorption of potholes and bumps
Firmer ride quality	Softer ride quality
More vulnerable to pothole damage	Better protection for alloy wheels

What is a good ratio?

In general, keep the aspect ratio for your vehicle. If your vehicle offers multiple wheel sizes, a higher diameter wheel will have a lower aspect ratio. Comfort is the biggest gain when the aspect ratio is higher. Within reasonable limits, put safety for you and your passengers first and stay within the sizes approved by the manufacturer.

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