The reason car tires are circles and why it matters

An egg-shaped wheel is not the best thing to have on your car.


Egg car

Why is a tire round? or, why are the wheels of vehicles made circular? Imagine your car having wheels in the shape of an egg. It is not hard to understand this would lead to not only a very bumpy ride, but also to possible damage to all parts of your car. Now, egg shapes can easily be seen and dealt with. But what about relatively small deviations that the human eye cannot trace, but you definitely will feel when driving? Because when your wheel is not centred in the right way and has somewhat of an egg-like geometry, the car’s suspension will follow this deviation. Of course, you can go to a garage and have your wheel balanced. This will do some good, but not very much because a balancing machine cannot emulate contact with the road. And then you are stuck with a balanced egg.

Is a tyre really round?


why is a tire round

There are also two other, and more effective, ways to ensure your ride is as smooth as possible. At the first level, there is the so-called matching of the wheel. Matching is meant to reduce parameters such as radial runout, lateral runout, force variation or imbalance. Matching or match mounting of tyres and rims is a process whereby the tyre’s installation position on the rim is specifically selected to minimise final force of imbalance. The tyre’s lightest spot is aligned with the wheel’s heaviest spot.

At a higher level, Tire Uniformity (TU) control is the way to go. Tire uniformity refers to tires’ dynamic properties as defined by a set of measurement standards and test conditions accepted by the global car manufacturing industry. These standards include parameters like radial/lateral and tangential harmonics force variations, lateral forces/radial and lateral runout geometry, and sidewall bulge.

Low and high speed: Balancing an Egg


Balancing an egg


For many years, uniformity testing has been performed at low speeds (about 8 km/h). However, today the suspension system of cars becomes lighter, and they are more susceptible to imbalances. Moreover, because electric vehicles are very quiet by nature, any irregularity in the tyres will immediately be felt inside the car. Add to this, the ever-growing customer expectations and you immediately understand the importance of tyres with optimum quality. This requires advanced testing. That is why Eurofit started to look into ways to go a step further and enable testing at high speeds. This required building a new machine as there were no known solutions in the market.

So, why is a tire round? For a smooth ride!  And the only way to get a tire and wheel as close as possible to a perfect circle is to test, test, test! Today, a fully functioning, a production-ready machine can perform a high-speed uniformity test in just 24 seconds at a speed of 120 kilometres per hour. So far it is especially important for testing tyres of high premium car models. For car manufacturers, high-speed testing can be a serious benefit. It ensures that their cars perform well and that the risk of very expensive tyre-related recalls problems is extremely low. It is the most effective way to prevent an egg-shaped tyre.




Do you want to know more about how the car manufacturer processes can influence the driver experience? Check out our blog post: Causes for Car Noise you May Have Forgotten!


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