I have a M3P.
I use a sound measuring tool, and use my Apple Watch quite a bit for frequent monitoring of road noise simply out of curiosity and because I love a quiet cocoon of an interior. I also am deliberate about keeping sound safe for my ears.
The M3P with 20” wheels is not super loud car, but it’s a little louder than my work vehicles that are late model Camery but only by 1-2 dec at most of on the same surface. These work cars also have very new tires all the time, and the base model 4 cylinder motor which is super quiet unless you’re at 6000 rpm because it has no power at all, has no power band, and you have to floor it to slowly pass someone. Then it sounds like it’s going to blow up. Just cruising at 80 it’s quiet though because it’s a tiny low power motor designed to run at 1000rpm gearing wise and make 40mpg.
Now on the negative, the stereo is terrible in the Camery so to get the listening level at s point to make the music sound ok, you end up with more decibels than the M3 to have a good audio experience. Win for the M3. The stereo in the M3 is very good without having listen very loudly which means, in my opinion anecdotally, as well as with my dec meter, the M3 catches up a bit with even some of the nicer cars I’ll mention later.
I had an RS7 and a Porsche Panamera Turbo S. The Porsche was a bit quieter by 1-2 decibels, but that is a very sound dampened car. These cars with my meter are 68-74 dec depending on road surfaces, and radio. I take measurements with and without because I try to keep my radio + car sound at safe levels for me ears.
My modified GTR was 84-86 dec with the radio on, on the highway a good 10 dec or so higher than anything I’ve driven on the highway. It wasn’t fun for cruising to be honest, and I’m a danger sound for long term exposure.
There are tons of factors that contribute. Keep in mind that with sound, sound on top of sound isn’t a simple equation. Adding 10 dec to something that is 30 dec doesn’t equal 40. Direction, type, frequency, and I’m not an acoustic expert, all effect the perceived noise too.
1) The lack of engine and transmission sound is a factor and does allow for a perceived increase of other noises.
2) You hear more wind nose because of item 1, and the M3 itself has more wind noise that other cars that I’ve owned. The glass roof, and frameless door windows allow for more wind noise especially from crosswind. For me, I hate wind noise, so even if the dec inside aren’t more than say another car, my perceived noise is higher because I hate to hear wind noise. The windows need to be adjusted correctly and I’ve even added a secondary rubber seal to keep the windows sealed tight. Made a huge difference.
3) There is tire noise in the M3P but even for 20” 35 side wall sticker tires less in my ears that other cars, which is especially interesting to me because wheel well appear to have no sound dampening material at all. Now maybe that’s because I’m focused on wind noise because I hate that.
4) The stereo is very good in the M3P. This coming from an Audi and a Porsche that had upgraded stereo options. The M3P is better than the Audi Bose system and on par with B & O (or whatever it was). It’s not as good as the $8000 Bermeister in the $200,000 Panamera (2012 model) that I drove, and that car had zero wind noise. But that said, I don’t feel as if I’ve taken a huge step down. The M3 doesn’t sound as good cranked as the Bermeister, but at normal volumes is more spacious. That’s compared to a $200,000 car. The stereo in the M3P is great, has some noise cancelling and other than wind noise helps to give the perception of a quieter cabin when it’s on. It allows for great quality at lower volumes which means overall less dec when listening to music than the less expensive Camery, and some other cars I’ve tested.
5) Sticky performance tires are always louder than other types of tires. Lower sidewalls, 20” wheels, all louder for road noise. Tires brands and models can make a huge difference even a dec or two. Pilot sports are the best tire for performance and wear. They are just fantastic. I’ve used them on almost all of my fast cars. They aren’t the most quiet of tire, but they aren’t the loudest either. Also keep in mind that once tires are 30-40 % worn they will get louder. At 50% significantly louder depending on the tire make and model. If you want less road noise, find a quiet all season and put on 19” wheels with a 40 sidewall. 35-40 sidewall is a bigger jump than 40-45 sound wise in my experience.
To be honest, my guess is you could improve the M3 drastically with sound dampening in key locations. My brother did this in his corvette and it was an incredible difference. I’m not talking about vibration dampening material like dynamat that people call dampening which it is not, though that stuff helps too. You need mass to absorb sound which does mean a little weight. He used mass loaded vinyl sheets in the wheel wells and under the carpets and it made a huge difference by about 3 decibels. That doesn’t sound like a lot but it is because of how it scales, and because of where the sound is taken out.
I think id some MLV was used in the wheel wells of the Tesla, it would make a huge difference, it’s just all open and resonate in there.
Anyway long post.
