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Tyre size calculator

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205 / 55 R15

All about tyre calculator

Do you want to improve the steerability of your vehicle and its stability on a slippery road? Or would you like to make its ride smoother and softer? There is no need in serious modifications to your car’s suspension. In most cases, to adjust the riding characteristics of your vehicle, you can simply equip it with tyres of a different size. Here we tell you about improvements that can be achieved by such tuning and explain why you need a tyre calculator and how to use it.

Key parameters for interchangeability of car tyres

  • Tyre width. It determines the contact patch area of the tyre and, hence, its grip properties. Cars equipped with wider tyres are more stable on dry paved surfaces. Wider tyres contribute to shortening of a braking path, minimize the risk of wheel spinning during abrupt acceleration. However, a wider tread can impair the vehicle steerability and increase fuel consumption. In addition, the speed at which aquaplaning can occur reduces. Cars with narrow tyres are less prone to getting into a rut. Also tyres of this kind ensure better off-road performance on snowy roads.
  • Sidewall height. The higher it is, the better are damping characteristics of the tyre. High profile tyres perfectly absorb impacts and ensure smooth and soft ride of the vehicle. Low profile tyres improve its steerability, dynamics, and maneuverability. Installation of higher profile tyres without changing the wheel rim diameter can distort the speedometer readings. So you should always check whether the tyres are interchangeable.
  • Rim diameter. It is related to the wheel rim diameter. As part of car tuning, car owners can change it by installing tyres of a larger diameter than standard ones. As a rule, this involves using tyres with a lower sidewall height. Basically, by changing the rim diameter and sidewall height, you can slightly increase or decrease the road clearance of your vehicle.

Car tyre marking

Two systems of units are used for marking the tyre size: metric and imperial.

The metric system is popular among European and Asian manufacturers. According to it, tyres are marked as follows: 265/75 R15 where 265 is the tyre width in mm, 75 – the sidewall height as percentage of the tyre width, 15 – the rim diameter in inches. The letter R indicates that the tyre is radial.

The imperial marking standard is mostly used by American manufacturers. An example of such tyre marking: 31×10.5 R15, where 31 is the overall wheel diameter in inches, 10.5 – the tread width, 15 – the rim diameter. R also stands for a radial tyre.

Why tyre size calculator is necessary?

Sometimes it’s rather difficult to choose the right tyres for replacing the standard ones. Because if you install too wide tyres or those with excessively high sidewalls, the wheels can start to contact the wheel arches or suspension parts. Moreover, in case of significant increase of the wheel overall diameter, the speedometer readings can be highly distorted. Therefore, the overall wheel diameter shouldn’t differ from your car’s standard value by more than 5%. In addition, there are limitations for the tyre width: it should correspond to the wheel rim offset (ET).

All these aspects are taken into account by the tyre size calculator/converter. All you have to do is to enter the basic parameters of the tyres installed on your car in the corresponding fields of the programme, and then simply click “Calculate”. A list of tyres that are suitable for your car will be displayed.

Moreover, the tyre calculator can convert inches into millimetres, so you can enter American marking in the search field. Also you can use a tyre interchangeability chart, however, the calculator is a more convenient tool.

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