For every driver, a smooth ride is the best way to go from A to B. Bumpy rides are not only bad for your car, but they are also for your physical and mental health. Therefore, it is important to keep your car (and yourself) in shape. But still, there can be moments that you feel vibrations while driving your car. When this happens on a back or dirt road, there’s probably nothing wrong. But what about vibrations when you’re driving on the motorway? Or when you hear noises you can’t figure out from where they come. In any case, there may be a problem with your tires or tire and wheel assembly.

What most people don’t know is that a tire is not a perfect circle. For starters, there can be geometrical defects. Because a tire is not perfectly round, the car follows the tire profile, which results in up and down movements. At the factory, this issue can be solved by finding the best tire and rim combination, also known as matching, or just changing the tire. However, not all car manufacturers add this step in their production lines, resulting in noises and vibrations for the drivers.

Secondly, mass defects can lead to vibrations because a tire is never 100% symmetrical due to its manufacturing process. That means there are differences in the tire and rim construction which result in different mass distribution. The difference can be tiny, but it leads to an imbalance. The imbalance increases and becomes very noticeable with speed; it is like a merry-go-round with all the kids sitting at one side. This issue is known to car manufacturers and tire shops, and they can solve it by adding the well-known counterbalance weights to the wheel. But, there is a difference in adding the weights manually or automatically. The greatest advantage of adding them automatically is that the machine places the exact weight precisely in the best place. Fully repeatable and 100% documented. Unfortunately, not all car manufacturers add the weights automatically.

The third issue is stiffness defects. A tire is actually a series of tiny spring elements. When driving, the spring is compressed when it comes in contact with the road and released again when there’s no contact. In a perfect world, forces between car and road would be constant. But in real life, this never happens. Radial and lateral harmonic forces during the turning of the wheel affect the functioning of the tire. Variations in stiffness determine the level of declining comfort.

How to prevent the causes for noise and vibrations

There are two ways to check if these defects exist, and two ways of solving them. The first one is determining the minimum quality (which in the automotive industry is called tire uniformity or TU) at low speed; the manufacturer usually checks this. To determine low-Speed TU performance (LSTU), the manufacturer measures the tire with a drum which simulates the load of the car at a speed of 8 km/h. The most important results are Radial Forces Variations. The problem with checking only low-speed tire uniformity is that no one drives at only 8 km/h!

The second way to check quality issues with the tire and preventing noise and vibration is at high speed. The process replicates real-life conditions. In this case, performance is measured with a drum that simulates the carload at a critical speed of 120 km/h. The most important results are Radial Forces Variations and Tangential Forces Variations (TFV). TFV cannot be measured with the LSTU method.

Eurofit is a pioneer in high-speed tire uniformity testing. The company developed a new machine that is able to test tire and wheel assemblies at high speed and at scale. Unfortunately, a handful of manufacturers only apply this method to their premium car models, even though electric vehicles and SUVs are as sensitive to noise and vibration as premium ones. Not to mention the larger the tires (and wheel assemblies) the more sensitive they become.

To know more about high-speed tire uniformity measurement and how it is done in the factory, read our blog post.

Known the manufacturing process before buying

A test drive is the best way to detect vibration and noise issues in the tire and wheel assembly. Try to assess driving performance on a motorway. Ideally, road conditions should be as smooth as possible. Driving between 110 km/h to 130 km/h, respecting the speed limit, makes any issue very noticeable.

To know more about the steps necessary to put together this vital car part and how it can affect the driving experience, check our Ultimate Guide.