Aspect Ratio is a critical component of the tyre size. It is written in the form of an alphanumeric code on the side of the tyre, along with other measurements. The aspect ratio is important to determine the best tyre for your car.
The aspect ratio of a tyre is simply the height of the sidewall in relation to the width of the tyre, represented as a percentage. You can ascertain it by dividing the section height by the section width. It is measured when the tyre is inflated at its maximum air pressure, placed on the right rim, and is under no weight load.
Here's an example -
Source: tyremarket.com/tyremantra/understanding-tyre-aspect-ratio/
In this case, the height of the tyre sidewall is 55% that of the tyre's width. Generally, the aspect ratio increases or decreases in measures of 5. A low aspect ratio means the sidewall is shorter, which directly impacts the vehicle steering capabilities. The aspect ratio is also known as the tyre profile.
Why does aspect ratio matter?
The aspect ratio determines the level of comfort and steering response of the tyre. With a low aspect ratio, the sidewall will be thinner, which increases the sharpness and cornering of the vehicle. The ratio can reach the lowest of 30 and not any more than that. The lower the aspect ratio, the quicker response of the steering from the wheel to the tread. It also produces a broader tread patch contact with the road. It increases stiffness while driving but improves cornering performance.
With low aspect ratio tyres, more vibrations are transmitted from the tyre to the suspension. Since there is less air in the tyre due to thin sidewalls, it cannot easily absorb the bumps and potholes on the road.
The standard aspect ratio is 75, which is used in most vehicles. Low aspect ratio comes in sporty cars that need to ride with excellent cornering even at high speeds.
On the other hand, a high aspect ratio means thicker sidewalls, leading to a comfortable ride. You can generally see these tyres in buses, trucks, and heavy vehicles. They have an aspect ratio of 90 to 95. The more the aspect ratio, the better the tyre will be at absorbing bumps and shocks in poor road conditions.
When replacing tyres, some people opt for low aspect ratio tyres because it provides a stylish look to their ordinary vehicle. It offers a classy and fine-cut look, making the car look extraordinary and sporty.
However, there always has to be a balance between low and high aspect ratio if you want good cornering capabilities with a comfortable drive. That's why most standard car tyres come with an aspect ratio somewhere between 60 to 75. It ensures that the sidewalls are strong enough to withstand shocks while offering sharpness in handling the vehicle. It delivers a good steering response even on rough road conditions.
Tyres can be mounted on slightly narrow wheel rims from their original size. The tyre width to calculate aspect ratio actually depends on the wheel width the tyre is mounted on. Therefore, the aspect ratio depends on the tyre section width changes and the change in rim width.