Low Frequency Road Noise Hunting.

[BourbonNcigars]

Yesterday in someone else's thread asking about getting an improvement in their sound system, I posted the graph below as an example of how one noise can overpower others. The measurement was taken yesterday in an effort to have some data and a starting point on why my ears ring after even taking a short drive in my 2010. Experience in audio has taught me what various frequencies sound and feel like, and the measurement confirmed my suspicion. I have a lot of LF information being produced by the vehicle. I suffer from tinnitus so I'm especially sensitive to noise. The red line indicates the max level, so the average would be slightly lower. Still bad, though (for my particular ears). This is at 70mph:




At idle the truck is plenty quiet.

So now I'm trying to determine what path to take in order to find a solution. First, I need a root cause. Obviously the problem comes up only when the vehicle is in motion. So that tells me to start with tires and suspension. (outside wind noise isn't at these frequencies). What I don't want to do is go at it without a plan. That's how costs creep up.

I do have some clues to start with and maybe some of you fine folks who know more about this particular SUV can help:

1. The truck is an SSV that originally had 17"s. The PO put on the factory 20"s.
2. The tires are half worn Goodyear LS2's in the rear, new Ironman(?) tires up front.
3. There is a slight vibration when driving. Can be felt a little but is noticeable watching the back of the passenger seat move.
4. All the suspension appears to be original (114K miles on it).
5. The truck does ride a little rougher on certain surfaces that I think it should.

Wildcard: Other Tahoes may measure exactly like mine. I have a plan with my wife's BF to drive and measure her 2011 LT and will grab her RPO's to see what suspension she has.

On the tires, I have not done anything with them in the 3 months I've had the truck. I drive mostly very short distances so I haven't pushed the issue of finding a solution to this problem until now, after taking a short road trip recently. It's possible new tires would fix the issue (or greatly improve it). It's also possible a simple balance and alignment would too. Found this on the Michelin site which was interesting given my current problem:



Could this issue be exacerbated by worn shocks or bushings?

The fact that it's an SSV may make many think it's a lack of insulation issue, but I don't believe that's the case. In pics and videos it doesn't appear that the upscale models really have that much more insulation anywhere. Removing a door panel looks the same as an LTZ panel. Maybe there's something in the body cavities? It has carpet and padding, though not factory so it lacks any backing that the factory carpet may have. But, low frequencies aren't going to be stopped by even large amounts of aftermarket sound dampening/blocking. They'll blow right through it. As an FYI, the cargo area is lines with a butyl backed material (Noico, a dynamat competitor). No CCF or MLV is on top as of yet. Just foam and carpet.

Haven't said all that, the first step seems to be to make sure the tires are balanced and the alignment is good. I see no odd tread patterns on them. But, with the somewhat worn LS2's on the rear and the dealership (or PO) putting on the cheapest possible front tires they could find, I'm hesitant to spend time and money on this. But it may be a bite the bullet scenario to see if it even partially remedies things.

I'll still list that as step 1.

What about the suspension? Is there anything wrong with putting 20's on a Tahoe that originally came with 17's?

Shocks/struts...could they be the problem at their age (114K)? I wouldn't think so, but it's possible. Are there any other bushings down there that may get worn and transfer vibration to the body?

Any help on this or theories you may have is appreciated. If I can't solve it, I have to get rid of it.

 

[Wolfbraid]

You might want to try and experiment with the tire pressures, upping them to +5 +10 or dropping them -5 -10 just to see if the noise levels change. I know on our road trips I up my PSI helps with fuel economy, and road noise and ride does change.

Also running 20's vs 17's you will have a difference in ride quality, generally speaking a 17 will ride nicer/softer than a 20. if you are using the same tire model on both. That being said I imagine there are some really $$ quiet riding 20's out there, Michelin probably being one of them.

Shocks and struts shouldn't produce any high pitch sounds, so I wouldn't guess those are related.

One last thing to inspect would be front wheel bearings, I just recently replaced mine, and they were obviously loud. I cursory inspection wouldn't hurt.

 

[iamdub]

In short, I concur with Eric.

To directly answer your questions with my opinions:

There's nothing wrong with 20s versus 17s. The overall diameter is what matters and they're very close to each other, assuming stock tire specs for each are held. Maybe the shorter sidewall of the 20s contribute to a difference in sound from the 17s. It certainly contributes to a difference in feel. Different brands and style of tires, their composition, age, amount of wear and especially the tread design have more to do with their road noise than anything.

I doubt the shocks and struts themselves have much of anything to do with this. If anything, I'd think the shocks and struts would absorb and isolate some of the vibrations. I don't see low frequencies traveling through a rod, then gas or oil (whatever style of shock you have), through a rubber mount, another bolt(s), the frame, body mounts, the body, etc. A more direct conductor would be the control arms, the rubber bushings, frame frame mounts, then body. But, still, I don't see low freqs traveling all that and still being strong enough for you to detect. I like the Eric's idea on the hubs/bearings.

I'd have to say the primary suspects are the tires and the body itself. That big ass length of sheet metal over your head could easily act as a transducer. Actually, I thought it was found to be the cause of the buffeting on the K2xx cars. It may not move enough to be seen (how would you see it anyway?), but something that large wouldn't need to move much to create waves.

 

[BourbonNcigars]

Thanks, guys. Data does point to the tires, but I haven't totally ruled out stiff suspension components. Going over small bumps at slow speeds excites whatever chain of events is causing this pressure wave I feel.

To Eric - I have tried changing the tire pressures. No measurable difference. Hadn't really considered hubs/bearings at this point since I don't really "hear" anything, as much as I feel it.

To Chris - The roof does make me suspicious. All I've done at this point is stuffed some stiff foam between the headliner and sheet metal to try and stop any possible movement/resonance there. Again, no measurable difference in LF info being produced.

It's not he buffeting experienced by the 2015+ owners, but rather similar to putting your head against a subwoofer playing a 20hz sine wave. Can't really hear it but you can feel it. Would be funny to find out Ironman tires are the worlds ********* tires and the source of my current inability to enjoy driving right now. No shit...I have one tab open on Amazon researching reusable ear plugs, and another tab open on local cars for sale. Never experienced anything like this in a vehicle before.

 

[PG01]

Try rotating tires for a week. Backs on front etc, then balance, theh alignment... but I doubt you need an alignment. Rotation is free and balancing is relatively cheap. Hubs can def be bad without you feeling them. They will make a high pitched squeal... 2 cents here and no book written....

 

[thompsoj22]

consider it being resonate to the vehicle cabin acoustics. you are riding between the tines of a tuning fork, try cracking an aft window slightly to subtly disrupt the frequency, a set of bridgestone turanza serenity plus tires will make an enoumouse difference, we ran these exclusively on our last MB and without a doubt they are "silent" on the road.

 

[iamdub]

To Chris - The roof does make me suspicious. All I've done at this point is stuffed some stiff foam between the headliner and sheet metal to try and stop any possible movement/resonance there. Again, no measurable difference in LF info being produced.

It's not he buffeting experienced by the 2015+ owners, but rather similar to putting your head against a subwoofer playing a 20hz sine wave. Can't really hear it but you can feel it. Would be funny to find out Ironman tires are the worlds ********* tires and the source of my current inability to enjoy driving right now. No shit...I have one tab open on Amazon researching reusable ear plugs, and another tab open on local cars for sale. Never experienced anything like this in a vehicle before.

I'm sure it's not the same buffeting and I'm more suspect of the tires. But, going back to the roof, there are structural differences between the two generations. Now that I think of it, not all of them come with the cross bars for the roof rack. This has been a complaint of some people that have bought them. This is just me speculating with my pessimistic/realistic perspective of stealerships, but it's like they come from the factory with them not installed, maybe in a box inside the vehicle, and the dealer stockpiles them to sell as an "option" to make a couple hundred bucks extra. I'm sure lots of people don't even know they don't have the cross bars. Anyway, I'm wondering if the buffeting is more common on those without the bars. Yours, being an SSV, means it doesn't have a roof rack. I wonder if that rack provides extra reinforcement and the newer generation is more sensitive to the lack of the extra reinforcement.

About the Ironman tires, they're nothing special. Just cheap Chinese rubber bladders to hold air and I doubt they have any real engineering involved. It's one of the brand names people get when they spend $2500 on new 24s and don't want to invest nearly that same amount in Pirellis or Toyos or whatever other highly regarded brand that carries quality low-profile large tires. Like many other Chinese knock-off items, they're probably made with the molds of top name brand tires after the patents have expired. They just change the sidewall stamps for the branding. They may have the same or nearly the same tread pattern and shape as the name brands, but the rubber composition and insides (belts, etc.) may be totally different which could lead to a noisier tire, among other quality deficiencies.

My OCD won't allow me to have two different brands and models of tires so I'd be getting a new set just to satisfy that.

After you test your wife's friend's LT, is there any chance she'd let you try her wheels and tires on your SSV? I realize swapping a full set of wheels is a bit of a pain. But it would be a thorough and "free" way to test. Especially if you put your wheels on her LT and retest it.

Lots of potential info here on which to get high...

 

[BourbonNcigars]

I'm sure it's not the same buffeting and I'm more suspect of the tires. But, going back to the roof, there are structural differences between the two generations. Now that I think of it, not all of them come with the cross bars for the roof rack. This has been a complaint of some people that have bought them. This is just me speculating with my pessimistic/realistic perspective of stealerships, but it's like they come from the factory with them not installed, maybe in a box inside the vehicle, and the dealer stockpiles them to sell as an "option" to make a couple hundred bucks extra. I'm sure lots of people don't even know they don't have the cross bars. Anyway, I'm wondering if the buffeting is more common on those without the bars. Yours, being an SSV, means it doesn't have a roof rack. I wonder if that rack provides extra reinforcement and the newer generation is more sensitive to the lack of the extra reinforcement.

About the Ironman tires, they're nothing special. Just cheap Chinese rubber bladders to hold air and I doubt they have any real engineering involved. It's one of the brand names people get when they spend $2500 on new 24s and don't want to invest nearly that same amount in Pirellis or Toyos or whatever other highly regarded brand that carries quality low-profile large tires. Like many other Chinese knock-off items, they're probably made with the molds of top name brand tires after the patents have expired. They just change the sidewall stamps for the branding. They may have the same or nearly the same tread pattern and shape as the name brands, but the rubber composition and insides (belts, etc.) may be totally different which could lead to a noisier tire, among other quality deficiencies.

My OCD won't allow me to have two different brands and models of tires so I'd be getting a new set just to satisfy that.

After you test your wife's friend's LT, is there any chance she'd let you try her wheels and tires on your SSV? I realize swapping a full set of wheels is a bit of a pain. But it would be a thorough and "free" way to test. Especially if you put your wheels on her LT and retest it.

Lots of potential info here on which to get high...

Figured as much on the Ironman tires. And actually, according to Tirerack anyway, the LS2's don't get stellar reviews when it comes to noise and comfort (and mine are over halfway through their tread) . Of course that'll vary from car to car. I think @Doubeleive said in another thread that he liked his LS2's. My OSD is the same...tearing me up having two different sets of tires. And crappy front tires at that. I could never do that on my own.

Once I get to drive the other Tahoe (and measure it), I'll know a lot more. Worst case is that it measures very similar and it's simply a Tahoe/me problem. Assuming it measures better, well....you know the saying...if you can measure it you can improve it. Well, as long as the improvement is cheap. I don't count tires as an added expense. Just a part of ownership that has to happen. But...

If it's not the tires, and I drop $1k on a set only to find out the problem is still there, then I'll be pissed. Makes an excellent case for trading wheels with her Tahoe. Would be an unfun DIY project but I have the impact and jack stands to do it. Just not sure how she'd feel about it. Down to earth gal, but that's kind of a weird request.

On a related note, I did visit the tractor supply store last night and picked up some rubber 1/4" stall mat material. Going to cut it and use it as you would regular MLV to block sound over the wheel wells and run some more noise measurements to see what happens. If it works, I can prove that it's a much cheaper alternative to MLV. If it doesn't, then I'm only out $36...but I have some 1/4" thick rubber.

 

[Doubeleive]

I think the poor reviews on the ls2's are from people with lightweight sedans, these tires work really well on these trucks, I had them on my nbs also probably wont ever change to another tire, but too each there own....

 

[iamdub]

It is a bit of a weird request. But, she's bound to be due for a tire rotation at some point. If that point is near, offer to hook her up.

I'm a cheap ass so I try to find new truck take-offs and get nearly-new tires AND wheels for about the same price new tires alone would cost. They're all over craigslist with people swapping the factory wheels and tires on their new trucks with aftermarket wheels. I know a lot of the newer ones are available with Continental all-season tires. The tread on them looks like it'd be quiet.