How to measure tire noise: At first glance, not many people will equate noise coming from the car directly to the tire. Most of the time people are more fixated to the engine noise which dominates the surrounding sound wave. However as we move towards electrification, there will be no noise coming from the engine anymore and thus leaving the tire as the dominant noise source.
EU label-Noise
Most of the reader might be familiar with the sound wave labeling system from the EU label. Let’s take a look at what the corresponding limits means.
| Tire width, T | A | B | C |
| T≤185 | N≤67 | 67<N≤70 | N>70 |
| 185<N≤215 | N≤68 | 68<N≤71 | N>71 |
| 215<N≤245 | N≤68 | 68<N≤71 | N>71 |
| 245<N≤275 | N≤69 | 69<N≤72 | N>72 |
| T>275 | N≤71 | 71<N≤74 | N>74 |
To be clear, what the EU label is showing the exterior noise. Hence from a consumer point of view having a low exterior noise tire might not benefit you directly but collectively it should benefit the environment. If you fancy a quiet interior car noise, this label indicative is definitely not something you should rely on. From the table above, you notice that the A B C classes are define separately based on the tire width. This reason is fairly simple, as the tire width increases, your contact area to the road surface also increases. This results in a higher frequency of air pumping resulting in a higher noise level. Subsequently a 275mm width tire has a +4 dB allowance more to hit label A compare to a 185mm width due to the same reasoning.
How do you measure exterior noise?
Pass by noise is one of the easiest things to measure. The picture above shows the ISO 362 standard of measuring pass by Noise. 2 microphone is place 7.5m from the center of the car while the car must roll with engine off & with a define speed (80km/h) for at least 20m along the center line of the microphone. The measurement is usually repeated 3-4 runs and the average is taken. One thing to note that the test must be done in a dry condition as the wetness of the road surface affects the noise results. The road surface also plays a big part in the measurement and it should adhere to standards define in ISO 362.
Summary
In the upcoming future, tire noise will play a major role in the overall contribution to the vehicle noise. Important to note that the EU label noise category is about exterior noise. Key factors affecting the pass by noise test includes tire width, test surface, speed and also the wetness of the track.