Harmonic Vibration Issue

[Tommyvee]

I’ve recently been experiencing a weird harmonic vibration that starts to resonate at about 40 mph and gets louder up to 45 mph and then disappears. I hear it more than feel it. I have the 20” 469 wheels. The car has approx. 11,000 miles. I swapped the tires/wheels for snows last winter so the tires probably have 7,000 miles on them and look good in terms of wear, so I don’t think the tires are the issue. I’ve done some non-forum searches and the one issue mentioned most is bad/worn wheel bearings. Has anyone experienced this? If so did you find a cause/solution?

[hayduke311]

Any resolution on this issue? My newly-acquired '14 X5 50i MSport is doing the exact same thing between 40 and 45 mph.

[F15GorDe]

I seriously doubt it's wheel bearings with such a low amount of miles on them.
Several hundred thousand miles and they should be replaced.
Nonetheless, they would be one thing to eliminate in the process to determine the cause of the problem.
Would be nice to know what the OP found to be the problem.

[Diper]

If got the same on my summer 20" Dunlops RFT, not on my CONTINENTAL 19" winter tires. But I've driven 49.000k at the moment of which 2/3 on the summer tires. I've forgotten when it started but could be in the same range as you mention, could be later as well. It all depends on what kind of tires you use.

[hayduke311]

I'm running Dunlop RFTs on the staggered 20" MSport rims. I'm definitely able to differentiate between road noise due to wide tires (my last 3 cars were an E46 M3 ZCP, an E60 M5, and an E90 M3) and what I'm hearing, which is a harmonic that hits between 40 and 45, particularly when decelerating with my foot off the gas and peaking at 43 mph. No vibration comes through, so although I'm going to take it in and have them do a road force balance, it's not acting like it threw a weight, but we'll see. On the bearing issue, the sound doesn't change if I turn the wheel of center, but again, I'll have them check that as well. Would love to know if somebody's already gone down this road before and figured it out so I don't have to spend too much time swilling bad coffee in the dealership's waiting room waiting for them to finish their process of elimination diagnostics.

[Diper]

What I meant to post is that it will happen as tires get older, they can start 'singing' in certain speed window. I learned to live with it but the next tires will be of a different brand.

[Alex S.]

One thing comes to mind - standing sound waves. Those you can experience in the bathroom with the tiles when singing in a low voice - at certain moment you hear the resonating noise at certain pitch. Think of the pipe players, etc.

So, as a wild ass guess:
- there is a chamber of a certain shape and resonating cavity which is a fixed variable in equation - under the fender space,
- there is a fixed size of the wheel generating sound - road noise
- and the only changing variable here is the pitch which depends on the speed and surface you are driving on.

You can go further and think of the shape of a particular tire/brand, clean or dirty car, wet or dry conditions, but the standing sound wave effect can happen in some cases anyway.

For instance, E note/pitch of 0 octave has the wave length of some 16.5 meters (roughly 53ft) and when you listen to the music in a small room this wave cannot make a full sinusoid cycle, so it gets split, duplicated, multiplied, etc., until it reaches certain point when harmonic distortion becomes obvious.

And what the sound engineers are doing when in the mastering rooms - they use some pads, standing waves absorbers, etc.

So, some people experience this effect slightly at different speed depending on the wheels, tires, driving surface, etc.

Just a wild ass guess. I've been wrong in the past

*disclaimer: putting alien objects under the fender may damage your vehicle

[Tommyvee]

Sorry that I missed the posts here. When I took it the vehicle to see my SA he claimed it was the tires and I should see if Dunlop would do anything for me. So I went to Just Tires (Dunlop dealer) to see if they would do anything. We ultimately swapped my Pirelli Scorpion winters which are on 19” wheels to see if the noise was still there or not compared to the Dunlops, we’ll the noise went away with the Pirellis on. So Just Tires filed a warranty claim with Dunlop, at this point I’m still waiting for the tires to arrive from Just Tires, they have some in stock but are having difficulty locating all four. It appears that Dunlop is willing to replace them, I just don’t have clarity from Just Tires yet if it’s at no cost to me due to any proration of use. I’ll post an update when I know more. At this point I’m patient because I have the Pirelli winters on right now.

[ajob]

Years ago I had a E70 X 50i and bought new Dunlop non-RFT tires.

I soon noticed a "droning" sound, not too loud, at 50-60 mph. The tire specialist tried himself, ruled out bearings etc, and we concluded that it was probably due to the tire's tread pattern being amplified by some resonance somewhere in the car.

These tires were otherwise so good (excellent grip, soft ride) that I learned to live with the noise - it gradually went away after some 2-3,000 miles.

[hayduke311]

Thanks, guys. The tires are relatively new (2K miles) so I'm going to see if I can get the dealership to buy them back on a pro-rated basis and replace with some non run-flats. That's plan A, and I'm not expecting it to be successful. Plan B is to monitor it and see if it changes with miles. Plan C is to dynamat parts of the wheel wells to see if that can eliminate the harmonic, but I think that's unlikely to work either. Alex, I totally understand your point (I have a Physics degree so what you are saying makes sense to me), but if I had to guess, the sound is being amplified by the mechanical components as if the vibration is at the fundamental frequency or a harmonic thereof of the axle components as opposed to the wheel well forming an acoustic chamber. But my wild ass guess is probably just as good as yours!

[hayduke311]

Update: Problem solved. Took it to the dealer and once they got it up on the rack it was quickly apparent what was going on. The aggressive camber of the wheels resulted in the inboard side of the front tires being worn down and the outside being unevenly worn. The net result was that, with a run flat tire and poor alignment, the vibration from a balding tire shot right up into the suspension. When I bought it used, it was nearly impossible to see the inside bead of the tire without getting it up on a rack, and even though I'm not thrilled at the cash outlay, the results were transformative.

I put on 4 new Continental Extreme Contact DW non-RFTs(NOT the DWS...I live in NC and have a 02 Jeep TJ with 33" mud tires for when it snows or is even remotely nasty) and the problem is solved. I had them stand the tires "straight up" but still within tolerances such that the stance is more neutral. First of all, the non-run flats make ALL the difference in the world. Quiet, no tracking in ruts/streetcar tracks, smoother ride, and traditional handling characteristics. Vibration is gone, and I couldn't be happier with the car. The Dunlop RFTs are garbage. The dealership said that they see those things getting only 10-20K of mileage WITH proper alignment, less without (obviously).

[MarineOh3]

Originally Posted by Alex S.

- there is a chamber of a certain shape and resonating cavity which is a fixed variable in equation - under the fender space,

This is what I was going to say...