[wt888]

Long story short, it worked but the results showed otherwise. Worth it if you like to work on cars, not worth it if you're expecting a Lexus LS.

When I was car shopping, I wanted a firm and responsive ride, it had to be manual, and prefer 6 cylinders to a turbo 4. I test drove the Genesis G70 sport manual, but ended up with a used M235i. The G70 is quieter, comes with the LSD, and has better steering feel, but the M235i was better in power, shifter/clutch feel, value (used car), and size. Unfortunately, I found it to have a lot more road/tire noise than I found comfortable. My car has 30k miles and 2014 dated Supersports that were giving a lot of tire noise roar on the highway that I found comfortable, and it was causing a ringing resonance in my ear that was giving me a headache. Tires are not cupped or flat spotted and I just did an alignment.

I previously added sound dampening material to the front doors and front wheel wells of my last DD, a VW Jetta, with great success. It wore 4 year old touring class all season Michelins Primacy. The weird thing is that although the soundmeter app on my phone (uncalibrated) showed slightly larger dB on the Jetta, it felt a lot quieter due to lack of tire roar and that low frequency resonance.

The M235i is my new DD and I have sensitive ears, so I wanted a quiet ride. I was inspired by Crutchfield's youtube video which showed about 2 dB reduction in cabin noise on their Ford truck per segment of roof, doors, floor, etc., for a total reduction of 9 dB, which is a LOT, https://www.crutchfield.com/S-urlo4b...ound-pt-4.html , so I decided to go all out on this one. I enjoy working on cars and had a few days off.

Before you reply "You should have bought a Lexus", refer to my shopping criteria. I used to DD a Porsche Cayman and while it was definitely the best car I've ever had in terms of driving experience, it wasn't as livable as a larger car, the stereo sucked, it was loud, worried about parking it, often scraped the front bumper on inclines, poor fuel economy, really expensive tires, and it still had a lot more depreciation left than I was willing to eat, etc.

I had identified most of the noise as tire roar, so I made sure to cover the rear wheel well area inside, and the backside of the front wheel well liners. While you can buy quieter tire models, and the age of the 4 year old tires was also a contributing factor, I wanted to save that for a later step and this stuff is my hobby.

So over 3 days, I removed the 2 front door cards, 2 rear seat side panels, headliner, seats, front carpeting, and front wheel wells. I used Nocio 80 mil (0.2 cm) thickness self-adhesive butyl mats, with Nocio green closed cell foam mats, 170 mil (0.4 cm thick). I ran out of the Nocio, so I doubled up on some old ebay soundproofing butyl mat I had. To do all this, I used roughly 50 sq. feet of butyl mat and 75 sq ft of foam, and spend roughly $130 + the leftover mat I had from the previous project (maybe worth $30?), and $30 for the factory door gap foam (the stuff on the 4 cyl and diesels, but not the M235i) https://www.2addicts.com/forums/show....php?t=1200964. You need a set of plastic trim tools to work on the car, they can be bought from harbor freight for roughly $5.

Some tips: clean everything with rubbing alcohol beforehand to make sure the self adhesive sticks. If adding soundproofing to the wheel wells, wash them first, then wipe down with rubbing alcohol. For obvious reasons, don't apply it to the inner side where it'll get blasted and reduce wheel clearance. I also didn't apply it to the chassis, instead applying it to the backside of the liners. You have to leave room to reattach the panels. Additional material turned them into an effective sound barrier to help reflect sound away. BMW made the rear section foam instead of hard plastic like the front - I just made it an even better barrier. The roof already had carpeting on it and I didn't want to remove it, so I added foam around it and to the headliner. In retrospect, I would have pulled the carpeting since it was falling off in the corners already, cleaned thoroughly since the mat will be upside down, added some butyl mat to the roof, then used new spray adhesive to reattach the carpeting.

My foam also wouldn't adhere to the backside of the headliner since it's a fibrous material, so I used some 3M 77 spray to stick it on. I also didn't feel like breaking the shifter so I worked around the center console instead of removing it completely. This led to some gaps under the console, as I only did the sides around the transmission tunnel instead of also the top. I also added the OEM foam seal between the fender and chassis, you can find details on this mod elsewhere here.

Regarding disassembly, I had trouble with was the 3 plastic expanding rivets on the outer lip of the wheel well liner at the fender. Push the middle part into the fender and the rivets will release. Then find the center plugs behind it for reuse. Mine were dirty and it was getting dark so I tried to pry them out and ended up replacing them. I also couldn't figure out how to remove the upper console on the headliner since it was different from the manual. Mine had 2 metal spring clips near the rear - use a screwdriver to simultaneously push both towards the midline of the car, then the rear will drop down.

In general, the butyl rubber mat was not effective at blocking sound. It's for mass loading and reducing vibration of the material. If you only use butyl mat the results are going to be very disappointing. It also doesn't have to have 100% coverage, only enough to change the resonance of the material. Dynamat recommends 30% coverage but a little more is better than too little. The car has tiny square from the factory and they're really inadequate, but work. The closed cell foam blocks and absorbs noise, but it has to have 100% coverage, or as much as you can. I found much better results from the foam vs. the butyl mat. Tire/road noise is mostly low frequency, so that's what you want to target with mass loading and blocking the path of noise.

I used my soundmeter app (uncalibrated) on my phone to measure before-after results, drove with climate control/radio off, and used the same ~1 mile stretch of highway, always in dry pavement. The phone was held above the shifter. There was often up to 2 dB variation in samples. This could be from ambient temps affecting tire noise, a loud car next to me, windy day, etc.

60 mph (n=5), mean dB of 68.7
70 mph (n-6) dB=71.6
70 mph (reverse trip) (n=4) dB=70.5

after adding sound dampening material
60 mph (n=2) 69 dB
70 mph (n=1) 70.4 dB

Even though I only had a few samples, it was enough to show me that I wasn't going to see the 9 dB that Crutchfield got. I suspect their Ford F150 had much less soundproofing to begin with, and they used a lot more material. For example, their test vehicle only had thin plastic as a water barrier behind the door card. The M235i has at least some foam. I also don't know exactly what speed they had this 9 dB reduction at. How many trials did they run? Was it over the same stretch of road, under similar conditions? In driving under different roads, I found 5 dB difference in that alone. Their video showed mostly low speeds and maybe they were driving over rough road to accentuate the difference? I also ran out of nocio mat, which I found very sticky and heavy (I found it to be a good product), so I used my older ebay mat, which wasn't as sticky and dense, on the wheel wells and rear panels, but I doubled it up to try to make up for it.

However, the car feels much quieter to me, and since the resonance of the tires on the highway was greatly reduced, and it's much quieter at 40 mph, I partially accomplished my goals. It just wasn't as much as I'd hoped, especially for the amount of work put in. I think it's because the car already has decent sound dampening. If you were doing this to a Corvette or Subaru, the lack of sound insulation on those cars would be more pronounced. I felt that adding a small amount under the thick foam and carpeting of the floor didn't do much, but the rear-sides and doors did, since those areas were the most uninsulated. I just can't back up my observations with data since I took my measurements at highway speeds which is where the tire noise and resonance noise was most offensive. I suspect if I took measurements at lower speeds I may have found some evidence. Around town, it's pretty quiet with very little road noise, and I feel the most noise reduction was up to 45 mph, not the low frequency highway roar that I wanted to reduce. Also, the dB meter app doesn't show what frequencies are reduced - low frequencies are good at sneaking by gaps, so I suspect the offending noises were reduced less than other noise. The noise character definitely changed.

What I wouldn't do again:
The BMW has thick foam under the floor carpeting which is way more effective than the 0.4 cm of foam I added, so I can't say if doing the floor made much, if any difference. Pulling the seats is easy, but the center console is more difficult. I can't tell if adding foam to the headliner and roof made much difference and doing headliners is best for reducing wind noise, not the road-tire noise that I found offensive. I just had leftover foam and used it up, but also hoped that perhaps the roof was reflecting noise back down into the cabin, and that this would help, especially since the roof has such little insulation. I can't tell if it did anything. The area under the rear seats is quieter, but not by much. The rear seat foam does a good job of absorbing noise.

What I would do again: The doors made a very significant difference. I added some mat and foam to the outer skin, and added complete foam coverage to the door panel. The stock HK system sounded SO MUCH better(my center channel is unplugged). The noise from the rear cabin is much less, which I attribute to doing the rear seat sides. They're easy to access and I added mat+foam to the outer skin, the wheel well area, and the inner metal skin. There also isn't much soundproofing in that area and I definitely noticed it. This is versus the area under the rear seats, which is covered by thick foam seats.

Attached are pics showing before and afters. Some were the 1/2 way point: everything except the headliner got both butyl mat+foam. The backside of the wheel well liner had spaces where could fit mat+foam without interfering with fitment, which is why it looks so patchy.

Future plans: once the supersports are worn I'll get quieter tires. New tires are usually quieter due to fresher rubber alone, but the Michelin 4S is supposed to be better than the supersports in every way. I'm not going to use all-seasons, not worth the performance drop for me, especially since living in the northeast, need to use a separate set of winter tires. Thanks for reading!

[Poochie]

Why would you bother doing all this; as far as I remembered the M235i is not loud inside. It's not exactly a tomb but It's definitely what I would consider subtle in comparison to say the M2.

I would argue that's it's quieter than the 228/230 because the motor doesn't have to work as hard.

Whatever makes you happy but this is overkill IMO.

[wt888]

Originally Posted by Poochie

Why would you bother doing all this; as far as I remembered the M235i is not loud inside. It's not exactly a tomb but It's definitely what I would consider subtle in comparison to say the M2.

I would argue that's it's quieter than the 228/230 because the motor doesn't have to work as hard.

Whatever makes you happy but this is overkill IMO.

Exactly, I had a few spare days and tinkering with cars is my hobby. Some people like spinning centercaps, some people like dress up carbon fiber parts that don't do jack squat, and some like modifying their cars suspension or power to levels they'll never use. I'm an enthusiast so overkill is my M-O

Also, I know my post was very long, but it explained that there is a certain resonating road noise that was ringing in my ear on the highway and I didn't feel like buying different tires yet. It's not just my car, another M235i I test drove before buying mine also had it. It was giving me ear irritation because my ears are sensitive to whatever set of frequencies this car makes. Some people cringe when fingers scratch on a blackboard, I never found it annoying. Your experience may be different, and this project greatly reduced that low frequency booming that was giving me ear irritation. On certain roads it was completely eliminated so this project partially achieved my goals, but the dB app doesn't reflect it.

[Aspen235]

Nice post, I have some of the same noico stuff and will add in when I do my speaker upgrade. I will have some left so I think I will go at the rear seat area based on your post.
I think quieter tires will be the best improvement. Too bad that lots of grip and lots of tire roar seem to go together.

[Aspen235]

Have you disabled ADS?

[wt888]

Yes, ASD disabled through coding. I will experiment with pulling the fuse but I don't hear any hissing. I would do the front doors before the rear seat side panels.

[aozer]

do you have runflats or MPSS? because when i switched from runflats to MPSS on my old 228i, the road noise was pretty much eliminated.

my 235 came with MPSS and is pretty damn quite IMO.

[msendit]

Originally Posted by wt888

Long story short...

Nice write-up, thanks for sharing!

When you had the og headliner and carpets off, did you weigh them by any chance? I've heard numbers close to 70-80 lbs thrown around for all the noise insulation, which sounds like quite a lot.

[wt888]

I have MPSS, no runflats. Roads in CT are a mix of good, acceptable, and moon crater (esp in winter-spring).

The headliner is fiberboard and very light. Almost no insulating value. This is why I added 2 layers of foam there. The foam is pretty light so it's not like it would affect center of gravity. The butyl stuff is heavy. There isn't much wind noise coming from the roof though.

The carpeting is heavy, dense foam and thick carpeting. I didn't weigh it, but for the entire car, 70-80 lbs of insulation sounds about right, if you include the rear seat bottom foam, which is doubles as noise insulation for the area below it. If I had done this project to a car w/little soundproofing like the Miata, BRZ/Scion FRS, Subaru impreza, the results would have been more dramatic.

[CP911]

This is madness. Reminds me of being in High School and Dynamat'ing my door panels when I thought aftermarket speakers and large subwoofers were worth what little money I had back then.

You must have very sensitive ears, little tolerance for white noise, or both, because these cars are already very quiet in my opinion. Like far quieter than a new WRX, Miata, etc. My bet is that your 5 year old hardened tires with 30k miles of tread wear are causing all the noise. Had you replaced them first, I think you would have gotten far better results without the need to go through all this trouble. As long as you are happy though!

[amw896]

my 235i is for sure quieter than my older is350. Cool dyi tho!

[DaleHeinz]

"I can do better in my garage than a company that spends hundreds of millions on research and development."

The car is going to sound how it sounds. I wouldn't spend the amount of time you spent writing this post to try and make my car quieter.

Really not trying to shit on this post, but all too often, we, as men, have the notion that we can do it better. Logic and reason be damned.

[Poochie]

Over in the M2 section, they snicker at how subtle the M235i sounds. It's almost an inside joke to say that your vehicle is 'quiet as a 235/240.'

There are owners who even added back all the sound deadening from the M235i to pipe down their interior drone of the M2.

Meanwhile, some folks here think the 235/240 are too loud. Humans..


Sound deadening https://f87.bimmerpost.com/forums/sh....php?t=1228618

[Sportstick]

Originally Posted by Poochie

Over in the M2 section, they snicker at how subtle the M235i sounds. It's almost an inside joke to say that your vehicle is 'quiet as a 235/240.'

There are owners who even added back all the sound deadening from the M235i to pipe down their interior drone of the M2.

Meanwhile, some folks here think the 235/240 are too loud. Humans..


Sound deadening https://f87.bimmerpost.com/forums/sh....php?t=1228618

Anything that doesn’t interfere with listening to Sirius or drone on the highway when modulating the accelerator is ok with me.

[albertw]

Originally Posted by DaleHeinz

"I can do better in my garage than a company that spends hundreds of millions on research and development."

Really not trying to shit on this post, but all too often, we, as men, have the notion that we can do it better. Logic and reason be damned.

People who make this type of post never seem to notice that the same criticism can be applied to every single mod they have made to their own cars.

I think it's form of cognitive dissonance, or at least related to it.

[wt888]

Originally Posted by DaleHeinz

"I can do better in my garage than a company that spends hundreds of millions on research and development."

...the notion that we can do it better. Logic and reason be damned.

Is modifying the car IN ANY WAY making it worse? Better is often a matter of taste. What's better for you may not be better for me. Is artificial exhaust noise distorting the stereo and increasing cabin noise better?

Just off the top of my head I can recall dozens of aftermarket products that address defects in German cars alone. For example, a guy in his garage started an entire mini-industry around fixing Porsche watercooled engines that Porsche never even acknowledged for over 10 years. I used to work on Volkswagen diesels for a living, and the dumpster fire that was the newer diesels also resulted in a mini industry fixing them, that started with guys tinkering in their garages, not at large engineering firms, and most definitely not at the auto manufacturer, which has since moved on. The sad thing is their diesels are now effectively orphaned in this country and those problems will be permanently ignored, making garage fixes almost necessary.

While I can't build a better car in my garage, I and most people who have modified cars, can make the argument their modified cars are now "better". The point of my post is that the change in sound wasn't reflected in the soundmeter app, which does not reflect a total failure of my project, but a shortcoming of my expectations and the testing equipment.

[Estoril6rod]

Originally Posted by wt888

Is modifying the car IN ANY WAY making it worse? Better is often a matter of taste. What's better for you may not be better for me. Is artificial exhaust noise distorting the stereo and increasing cabin noise better?

Just off the top of my head I can recall dozens of aftermarket products that address defects in German cars alone. For example, a guy in his garage started an entire mini-industry around fixing Porsche watercooled engines that Porsche never even acknowledged for over 10 years. I used to work on Volkswagen diesels for a living, and the dumpster fire that was the newer diesels also resulted in a mini industry fixing them, that started with guys tinkering in their garages, not at large engineering firms, and most definitely not at the auto manufacturer, which has since moved on. The sad thing is their diesels are now effectively orphaned in this country and those problems will be permanently ignored, making garage fixes almost necessary.

While I can't build a better car in my garage, I and most people who have modified cars, can make the argument their modified cars are now "better". The point of my post is that the change in sound wasn't reflected in the soundmeter app, which does not reflect a total failure of my project, but a shortcoming of my expectations and the testing equipment.

"Why not just get an M2?" I'm surprised no one has comes along with that classic question whenever you try to do something to improve your M235i/240i... Don't waste much time on the negatives, EVERY single owner or enthusiast has tried to do something extreme to their car, whether its making it as silent as a padded room or loud and droney like a stripped race car. I myself am looking into upgrading my suspension and its that journey of gathering info and going through different setups that makes everything worthwhile and enjoyable! Would i prefer to jump straight to an M2 Competition or a GT2RS for example? ABSOLUTELY! But that's neither a goal nor a possibility at this time and surely not a deterrent to the enjoyment of my current car!

[DaleHeinz]

Originally Posted by albertw

People who make this type of post never seem to notice that the same criticism can be applied to every single mod they have made to their own cars.

I think it's form of cognitive dissonance, or at least related to it.

Perhaps. That's why I used the word "We" when writing this post, to include myself. The responses have been a bit off the mark.

Just merely making the point that more often than not, we are not going to be able to do better in our garage that a multi billion dollar manufacturer. It's almost ingrained in most of us to think we can or at least feel the need to try to improve things, sometimes going against logic and reason.

I'm amazed that the OP spent that much time on this project. Bravo to him for sharing it though. It's useful information that we can all use to make our own thoughts and judgments on. Peer review, in a sense.

[Sportstick]

Originally Posted by DaleHeinz

Perhaps. That's why I used the word "We" when writing this post, to include myself. The responses have been a bit off the mark.

Just merely making the point that more often than not, we are not going to be able to do better in our garage that a multi billion dollar manufacturer. It's almost ingrained in most of us to think we can or at least feel the need to try to improve things, sometimes going against logic and reason.

I'm amazed that the OP spent that much time on this project. Bravo to him for sharing it though. It's useful information that we can all use to make our own thoughts and judgments on. Peer review, in a sense.

Having worked at one of those places, I don't think the idea is that an individual can do "better" objectively. It's that one can do "better" for themselves. The mass production solution is inevitably a compromise of cost and desired outcomes. For example, I don't think my car is "better" because I removed the original lower control arms to substitute the M3/M4 version (from Turner Motorsport). it's just more to my liking, realizing many general BMW buyers would find the car far too sensitive to steering input. I happen to like it this way. One can apply this analysis to most mods, taking the car from the moderate median of satisfaction for the range of BMW buyers to the specific recipe each of us prefers. This goes back to a debate we had long ago...no vehicle, no mod, is "better" than another...they are just different, and each of us has a personal subjective evaluation to make on whether a set of attributes is more/less desireable.

EDIT: Just thought of a great analogy...have fun with this one: When you go to a restaurant (usually among the most upscale) that will not place a salt nor pepper shaker on the table because the chef is the expert at the proper flavor profile, do you accept that? The moment you make the first shake of either dispenser, you have overruled years of culinary training to "make it your own". Is that OK?

I will say that the OP's work and post shows an incredible dedication and attention to detail that will serve well in all other future endeavors!

[DaleHeinz]

Originally Posted by Sportstick

Having worked at one of those places, I don't think the idea is that an individual can do "better" objectively. It's that one can do "better" for themselves. The mass production solution is inevitably a compromise of cost and desired outcomes. For example, I don't think my car is "better" because I removed the original lower control arms to substitute the M3/M4 version (from Turner Motorsport). it's just more to my liking, realizing many general BMW buyers would find the car far too sensitive to steering input. I happen to like it this way. One can apply this analysis to most mods, taking the car from the moderate median of satisfaction for the range of BMW buyers to the specific recipe each of us prefers. This goes back to a debate we had long ago...no vehicle, no mod, is "better" than another...they are just different, and each of us has a personal subjective evaluation to make on whether a set of attributes is more/less desireable.

I will say that the OPs work and post shows an incredible dedication and attention to detail that will serve well in all other future endeavors!

Again, the response is missing the mark a bit. Maybe I didn't write as clear as I had thought. That's on me.

I'm not talking about buying a part and modifying our cars. This isn't the old Mod Vs Mod-free car argument. I'm talking about us going into our garages and coming up with an original solution to a "problem" ourselves. In that instance, we are rarely going to be able to do better than the manufacturer. I'm not making absolute statements, but the responses have included that assumption.

The OP stated he didn't get the results he thought he would. Thus my original comment that we sometimes think, against logic and reason, that we can do better than the manufacturer. And he showed that "better" was not quantifiable in this instance.

Is he happy with his results? It seems like he somewhat is, so that's why I said I wasn't trying to shit on his post. More power to him, but i can't imagine spending that much time and effort myself for something that seems to not be noticeable to most people.

[LuvMyE92]

Thanks wt (OP) for the long but very informative post. Like you, the "white noise" bugs the crap out of me, and so I'm going to do some sound reduction to my M2. I've been doing lots of research, reading the various threads relating to this, and its information like yours that helps the rest of us decide what parts give the best band for the buck.

That's what these forums are (or should be) about; sharing knowledge, tricks, experience and results.

[sethwas]

Originally Posted by wt888

Future plans: once the supersports are worn I'll get quieter tires.

This was a good write up.

I can tell you the car is very sensitive to tire choice. If you are serious about having a quiet ride then you need to simply buy the quietest tire as the impact will be drastic - especially with the mods you made.

You are going to want to avoid a UHP or max performance tire altogether. They simply aren't optimized for noise as that's not a criteria the purchasers of those tires want.

Move down to a grand touring tire - this will be an all season but the performance is still up there. Something like a Michelin Premier A/S or even quieter the Bridgestone Serenity. Unfortunately you will lose the ability to run RFT's if that's a concern.
I know you mentioned you're concerned about it but on the street you won't see a performance hit and your ride comfort will go up. The car will 'feel' different with different shoes but that boils down to preference between brands and isn't an objective measure.
Just like BMW 'could' have made the 2 super silent but decided to save the money since they could charge the same and leave out deadening as they felt it wouldn't be desired by the customer base.

What size tire are you currently running?

Seth