Noise, vibration, and harshness. (NVH)

[JRouche]

Had a friend here recently ask me if I had a problem with NVH because I use metal to metal mounts for my sway bars. Got me thinking...

I have a metal bushed sway bar at both ends, my rack and pinion steering has the rack mounted with steel bushings, my front control arms use metal bushings, my watts link uses metal heim end links as does my parallel four link.

So my answer was no, I dont feel ANY of the "road trash". Like small gaps in the road, small pot holes, any heavy lines on the freeway or any of the common road trash thats seen while driving, even small road roughness. I just dont feel it in the steering wheel, floor pan or any other part of the car. Its pretty darn smooth. Like driving on air, and I am, air springs.

So I was thinking because I have air springs if that might be a part of it.

My thinking is a car that has steel coil and leaf springs might transmit alot of the road noise to the body and driver??

It might not be all the other suspension pieces transmitting the road noise to the driver but the MAIN steel part thats suspending the car, the springs!!!

So anytime someone introduces a suspension part on the car how every small the transmission of road noise might be, it sounds and feels like you are driving a tank downtown.

I think the MAIN contributor to NVH is the steel springs. And yes, there are the rubber donuts in between the perch and spring. But anyone that has removed 20-30 year old coil springs know they are super hard and compressed, they dont do much to dampen any vibration or road noise at that point. When new they prolly do ok, depends on the design, they might be good for five years. But there is so much force and the material changes so they become useless for the original objective.

My point? It might not be the other connections of the suspension that cause alot of NVH. It might be better to look at the spring dampening pads or an air spring VS ditching the idea of using metal to metal connections for some of the other suspension parts that could benefit with a stiffer joint, like metal on metal or even some harder bushings like delrin.

I think more work is needed to remove the direct road noise from the steel springs before we ditch the idea of using stiffer joints on some of the other suspension parts. Because I think there is a large ammount of preformance gain to be had with using stiffer mounts on the other suspension parts without sacrificing with more NVH.

Just a thought... JR

[NightDiver]

I would also consider the surface of those suspension parts connected to each other. Two machined, relatively smooth metal surfaces make almost no noise when rubbed together whereas rubber, because of its porous nature, squeaks when rubbed against almost anything. While rubber is a better insulator against vibration which you can feel, it can induce more noise that you can hear in the process. For example, a good set of radial tires may do a lot to dampen vibration from the road, but step on either the accelerator or the brake too hard and think about how loud those same tires scream....

NVH is something that we will always have as long as we are driving. We can go to softer tires to avoid picking up road vibration, but they wear out faster. We can go to softer bushings, but again, they create their own noise, wear out faster, and allow more flexing and loss of responsiveness. We can install Dynamat, Second Skin, or other similar products, but then we add weight to our cars. It all comes down to personal preference. What noises can you live with, how responsive do you want the handling, and how often do you want to change the parts involved? Once someone has answered these questions, and decided which is most important to them, they can determine which parts they want to build with.

[DarkoNova]

I think it's mainly the leaf springs. Everyone I've talked to that's ditched the rear leafs for a 4 bar/link (or anything that doesn't use leaf springs, really) says the car rides much softer and doesn't transmit as much noise. Which is why I can't wait to get rid of my leaf springs.

One thing that really transmits NVH is the tranny mount. I remember putting 75D bushings everywhere in my BMW, and I never felt any more vibrations or heard anymore noise than when I was using the stock rubber bushings. Then I switched to solid steel motor mounts. Still nothing new. Then I put in a 75D tranny mount and BAM, I could feel every bump in the road, and the car would shake when I revved it. Don't ask me why that one bushing made the biggest difference, but ever since then I've told everyone to just stick with rubber for the tranny mount, unless they have a problem tearing the mount.

It was kinda cool, though. Felt like the Nova, when I revved it and the whole car moved, lol.