E39 B10 Intrusive road noise. Is there a cure?

[Andrew Bluett-Duncan]

Thinking about the width of the tyres and the noise they transmit, do you know if it's possible to swap the wheels on my 525d Touring for the Alpina ones to see if the same noises come through, will they fit ok do you happen to know? They are 235/45 17"

I think that would be a very interesting experiment Andrew and provide some excellent feedback - I've never heard of that being done before so swapping the same set of wheels and tyres onto 2 different E39s should give the same noise levels on both cars!

Thanks for the encouragement Barry, I'll report back on what I find...!
Kind regards
Andrew

[bobbly]

It manifests itself as either an almost ringing quality on certain surfaces, or an intrusive drumming sound on others, which is a disappointment as the car is otherwise very quiet on many road surfaces and gives a far more comfortable compliant ride then my touring .

Sounds very much like the tyres are transmitting the road surface (excitation) forces into the body of the car. Depending on the road surface (coarse surface giving a lower frequency force, fine surface giving a higher frequency force) the car is responding by the resonant frequencies of the various parts of the car that are tuning in to the force and resonating; which makes the noise. Noise is actually all vibration and is movement of air molecules creating sound as a result of the force. Low frequency noise and vibration carries more power and is usually more noticeable as a result. High frequency noise and vibration carries less power and is often less noticeable, but can be very annoying (think mosquito....). Note that some road surface textures can be so random they create white noise excitation, and that's an absolute nightmare on a sensitive vehicle as all resonant frequencies are excited and hence respond in kind if bushes are worn or fixings loose or missing on components (modern cars are dynamically designed to not respond to forcing which humans are sensitive too, but this changes over time and maintenance regimes)

It may be therefore that there is some loose trim or similar or even worn suspension bushes which are allowing the road noise to transmit more freely into the car structure. It may be worth a good poke around the suspension rubbers and see if a) they're in good order or b) they've been exchanged for poly bushes.

Cheers
Bobbly

[Andrew Bluett-Duncan]

Sounds very much like the tyres are transmitting the road surface (excitation) forces into the body of the car. Depending on the road surface (coarse surface giving a lower frequency force, fine surface giving a higher frequency force) the car is responding by the resonant frequencies of the various parts of the car that are tuning in to the force and resonating; which makes the noise. Noise is actually all vibration and is movement of air molecules creating sound as a result of the force. Low frequency noise and vibration carries more power and is usually more noticeable as a result. High frequency noise and vibration carries less power and is often less noticeable, but can be very annoying (think mosquito....). Note that some road surface textures can be so random they create white noise excitation, and that's an absolute nightmare on a sensitive vehicle as all resonant frequencies are excited and hence respond in kind if bushes are worn or fixings loose or missing on components (modern cars are dynamically designed to not respond to forcing which humans are sensitive too, but this changes over time and maintenance regimes)

It may be therefore that there is some loose trim or similar or even worn suspension bushes which are allowing the road noise to transmit more freely into the car structure. It may be worth a good poke around the suspension rubbers and see if a) they're in good order or b) they've been exchanged for poly bushes.

Cheers
Bobbly
[/quote]

Hello Bobbly
Thank you very much for your thoughts and explanations on sound, much of which I can relate to. When you summarise in mentioning the suspension bushes you refer to Poly Bushes? If they are poly bushes will I be able to identify them easily and do I understand therefore that they're are not to be recommended? I seem to recall reading somewhere that they are long lasting but much harder material?

Interested to hear your thoughts.
Kind regards
Andrew