Every car, motorbike, bicycle or truck has them in order to be able to move: wheels. Wheels seem a given for any vehicle as they more or less all look alike – with the exception of super or luxury cars where they often are a fashion item. But what is a wheel exactly? How is exactly a car wheel put together? Does a wheel include a tire? How is the tire installed on the wheel? What is the tire and wheel installation process?
Let’s first clarify some terms. Wheel and rim are often used as words with the same or nearly the same meaning. Technically speaking this is wrong. The rim is not the whole wheel but only a part of it. It’s the cylindrical outer edge, holding the tire on the wheel. (Read more on this in our blog post What is a TWA?)
In the past, the process of assembling tires and wheels into so-called tire-wheel assemblies or TWAs, including all the aspects of the mounting process, used to entail many manual steps. However, today assembling TWAs at industrial scale is a mostly-automated process, with a strong focus on quality, efficiency and high volumes production. In the end, we all want to drive a vehicle that is both safe and comfortable.
Eight or nineteen steps to install a tire on a wheel
What does this process of tire and wheel assembly look like? Depending on the type of tire and wheel assembly, it either takes eight or nineteen steps. For a regular car TWA, we start with feeding the rim towards the machine and adding the valve. Next, the tire is fed to the machine. To ensure a smooth assembly the wheel and tire are lubricated. Then, the tire is inflated. When that is done, the tire goes into the balancing machine to ensure safe and comfortable driving. The reason for this is that wheels and tires are never precisely the same weight all around. First of all, there is the valve’s stem hole that can cause imbalances, and then the type of valve mounted (rubber/metal and TPMS) has a significant weight difference as well. This can be solved by putting balancing weights on the wheel. This will prevent vibration in the car, but also irregular damaging wear on the tires. Now, our basic wheel can be stored or transported to the car manufacturer.
Additional steps for the best tire and wheel assembly
Not all cars are the same. Next to the average city or family car, we have more luxury models that also have more sophisticated tires performance. For these types of tire and wheel assemblies, we have in total eleven additional steps that all contribute to a higher quality level. In addition to very specific technical measures such as rim run out and the bead seating the uniformity of the tire is checked. The rim run-out checks the roundness of the rim bead area edges. Whereas the bead seating optimises the bead, in other words, the edge of a tire that sits on the bead area of the rim. Tire uniformity refers to the dynamic mechanical properties of tires. The industry has defined a set of measurement standards and test conditions to enable standardisation and quality assurance. By measuring uniformity, only a TWA with the right quality level is put onto cars.
Low and high-speed uniformity
There are two ways to measure uniformity: at a low and at a real driving speed. For years, uniformity testing has been performed at low speeds (about 8 km/h). The most important results are radial forces variations. Today, as customer expectations on comfort have grown and car manufacturers want to meet these expectations, testing at high speeds has become key in delivering the right tire and wheel assembly for premium cars.
Eurofit developed a machine that can perform a high-speed test in just 24 seconds at a speed of 120 kilometres per hour. In traditional lab settings, the same test would take approximately 15 minutes for each tire and wheel assembly. The machine is used in Eurofit’s Böblingen plant that caters for the high premium models at Daimler, including the new S-Class models. This development underlines Eurofit’s number one commitment: delivering the perfect tire and wheel assembly. You can read more about this development here.
To summarise, a tire and wheel installation process takes a lot more knowledge and experience than most people realise. Next time you drive and experience any vibrations, consider there may be imbalances in the tire and wheel assembly itself.