Acoustic cotton isn’t a new thing in the tyre industry. It dates back even before Tesla Model S releases in the year 2012 (Model S original equipped tyres come with acoustic cotton). A number of luxury vehicle brands such as BWM and Mercedes-Benz come with acoustic cotton in their bigger size tyre (those R20 and above).
Before explaining what is acoustic cotton and how it lowers down the tyre noise, we need to learn how noise is generated from tyre.
Tyre Noise
Noise generated from tyre comes from two different sources as external rolling noise and internal noise.
Tyre External Rolling Noise
When air flows through the tyre tread, the tread on the tyre may disrupt the air movement, causing air vibration. The more tread design a tyre has, the more air is disrupted. This leads to higher noise when air vibrates rapidly*. Therefore, all season / all weather / winter tyres are generally nosier than summer tyre.
This also explains why tyre models with different tread pattern design can have different noise level.
Tyre ages and wear off cause noise level to increase. Harder rubber makes more vibration on the road. With lesser tread, the design of the tread that try to break the sound wave lose its effectiveness.
The value of these external rolling noise can be found in EU tyre label, Thai tyre label and soon Korea tyre label as well.
*If you want to learn more about why air vibrates causing nosier level, I will write another article about the law of gas in physics.
Tyre Internal Noise
Noise generated inside the tyre that will be transferred into the vehicle cabin.
Imagine you are inside an empty room say “ah”. The “ah” sound will echo throughout the room and it gets loud. High‑performance tyres are built with harder compounds for speed, and the sidewalls are stiffer as well. This rigidity causes sound waves to rebound and amplify more inside the tyre. As a result, high‑performance tyres are inevitably noisier than touring (comfort‑oriented) tyres.
When the tyre makes contact with the road, sound is generated like you speak “ah” inside an empty room. The sound gets transfer in the air inside the tyre and creates a louder noise upon knocking each other (in the air molecule).
That’s when the acoustic cotton comes in to resolve the internal noise level in the tyre.
What is acoustic cotton?
It’s a foam stick inside the tyre to block the sound from transferring in the tyre. It’s like something to cover up your mouth from saying “ah” in the empty room.
Each different brand have different types of foam. All of them claim to lower down the internal noise but with different values.
- Michelin claim to lower down the internal noise level by around 20% with its Michelin Acoustic Technology.
- Continental said its ContiSilent reduces the noise by up to 9dB.
- Pirelli states that its PNCS (Pirelli Noise Cancelling System) reduces noise by between 2 – 3 dB (already reduces the perceived noise by half).
Does it really work?
After years of customers feedback and experiment by myself previously, acoustic cotton functions work great on Electric Vehicle and European made vehicles that are good in blocking sound in the cabin.
Other conventional vehicles like Toyota Estima can’t enjoy the full functions of acoustic cotton. Afterall, I actually did an experiment some years ago by taking out the cotton from Michelin and Continental and stick it on my tyres.
Continental UC6 self-glue acoustic cotton
Pirellu p7c self-glue acoustic cotton
Acoustic cotton on the wheel?
Zeekr 7x and a few (same car brand) are probably the only one in the world that put the acoustic cotton on their original equipped rim (see image below). I have thought of this as well when I experimented the foam some years ago.
Nevertheless, this pose a problem rather than benefit on both the driver and technician.
- Technician needs to break the bead into the wheel using the blade. The blade have a possibly go deeper into the wheel and damage the acoustic cotton. The cotton on the rim is also a hinderance on dismounting the tyre.
- Acoustic cotton has weight that will add onto the rim. It will affect driving experience directly especially on hard cornering. Though, wheel balancing can still be done.
Going back to the empty room, do you think covering up your mouth is more effective than covering the wall to lower down the noise?
Noise is already generated and started to amplify in the tyre without the cotton on the tyre. When sound energy reaches the rim, the cotton on the rim can’t block all the sound. It becomes much less effective. Afterall, internal noise transmitted to the vehicle cabin not just by conduction in the rim.
Conclusion
If you want absolute low sound in your driving, acoustic cotton has to be one of the features in the tyre. Tyres like Dunlop Sport Maxx Lux, Michelin Pilot Sport EV, Bridgestone T005 EV are equipped with acoustic cotton.
It’s also important to take note that Electric Vehicle Tyre does not necessarily come with acoustic cotton.
Even if your desired tyre does not equip with acoustic cotton, you can think of self-glue acoustic cotton on your purchased tyres. However, these products may not work as these add-on technology are not tested with the tyre brand. I also came across a number of tyres with original equipped acoustic cotton actually came off halfway (image below).
Questions That You May Not Think Of:
1. How acoustic cotton came off halfway?
A: Glue loses stickiness due to heat and aging. Tyre aging also affects the glue bonding between the tyre and the cotton.
In addition, cotton may get wet before installation. If it’s not dry up before mounting the tyre, the water inside will accelerate the tyre and glue aging. Besides, water trapped inside the tyre will not evaporate.
Furthermore, tyre puncture may cause water diffuse into the tyre.
2. How does acustic cotton tyre get patched?
A: Tyre puncture in acoustic cotton can still be patched. However, the acoustic cotton has to be cut off in that area for tyre patch.
In fact, Yokohama actually advise drivers to replace the tyre if the acoustic cotton tyre is punctured. Continental also states that it never recommends tyre patch if punctured.
Tyre repair note from Continental Tyre
I will talk about the two methods of tyre patch (plug in vs internal patch) in another article.
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Other related articles:
-> Tyre Tread Pattern Explained – Asymmetric , Symmetric, Directional
-> Learn Types of Tyre – Summer, All Season, All Weather, Winter
-> Two main tyre categories – High Performance vs Touring
Other articles:
-> Tyre related information
-> Automotive Battery related information
-> Vehicle maintenance and DIY
-> Global Travel Guide
