Reduce, Reuse, Recycle: Deadening a Daihatsu Mira Cocoa Part 3 - Road Noise Deadening: Things We Take for Granted

This is a story about swapping cars with my child and improving that car, a Daihatsu Mira Cocoa, in my own way. This is my first experience owning a kei car.

I am constantly impressed.

I have added MT-10 friction-reducing additive to the engine oil and the same additive to the CVT oil to maximize power performance, and I have addressed noise at its source.

I also performed bulkhead deadening by adding sound insulation and sound-absorbing materials.

I also performed engine room deadening.

I carried these out.

Recently, I often take long trips, for example from the Kanto region to the Kinki or Chugoku regions, so I have set the tire pressure higher for highway driving. As a result, road noise on rough road surfaces became very noticeable.
Due to the repair shop's circumstances, I couldn't get Bridgestone tires and was restricted to Yokohama tires, so I am using a tire called dB (decibel), which is equivalent to the quietest version of the Regnos that Bridgestone developed jointly with the University of Tokyo. However, because the interior of the car became so quiet, road noise became the primary source of noise by comparison. That is how dramatically quiet it had become.

Applying sound-absorbing and sound-insulating materials to the tire housing is an option, but first, I wanted to suppress the generation of noise from the tires themselves.

As a physicist, I start from the source...

Since they are already quiet tires, what should I do? I thought that if the tire pressure had increased and the tires had become hard, I should soften the tire rubber. I decided to use KURE Engineering's Rubber Protectant, which I already use to prevent rubber deterioration, to increase the flexibility of the rubber.

Specifically, I chose a week with a warm weather forecast where the applied Rubber Protectant would not be washed away by rain, and where temperatures were high, to begin the application. In the evening, right after returning from an outing and with no plans to use the car afterward, while the tires were still warm, I sprayed plenty of Rubber Protectant on the sidewalls and especially on the tread surfaces. I was careful to move the car back and forth a little to ensure there were no missed spots. Of course, I also made sure the Rubber Protectant soaked well into the small grooves.

Then, I let it sit overnight. The next day, when I used the car, the road noise had changed drastically. Even on permeable pavement roads and rough road surfaces, there was almost no road noise. What surprised me most was a road with continuous curves and orange bumps on the road surface for speed control. It absorbed the vibrations supplely and the shaking was drastically reduced; of course, the road noise was also drastically reduced.

It was moving.
(To express it in modern terms, maybe it's "insane" (lol))

It was so dramatic that I couldn't believe it changed this much just from the Rubber Protectant treatment.

It is simple, inexpensive, and extremely effective, so I introduced it. Please give it a try.

Postscript
Once you have done this much work, you can enjoy classical music even in a kei car. Especially when driving at the speed limit on the highway, the delicate expressions of pianissimo are no longer lost to noise. Of course, it is also fine on mountain roads with continuous speed-control bumps.

Extra Postscript
I have no choice but to report this to KURE Engineering and thank them (lol)