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      09-24-2011, 10:23 PM   #23
ex10psi
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Quote:
Originally Posted by Emil View Post
i had a similar problem and could not find a solution. all components were balanced peefectly. no success. i talked to a very experienced bmw engineer and he told me something very surprising:
first of all, the m392 is very sensitive for vibrations. but in my specific case the vibes were caused by aerodynamic effects, not by misbalancing. by mounting spacers (or wider tires as in your case) the air hits a bigger part of the tires outside shoulder. now some shoulder tread profiles tend to drag the air more than others. the ps2 tires seem to be known for building up some kind of resonant peak in specific speed ranges due to a different to stock air stream. maybe that could be the reason in your case too.
i've not heard of this before... very interesting! hard to believe but hell, what do i know, i'm no engineer.

i'll be swapping rear wheels up front tmrw and will report back
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      09-24-2011, 11:50 PM   #24
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Well I think that's a possible issue. Fluid dynamics has some very interesting effects. But I can't speak for everyone's elses issues, but as for mine. A 12mm wider stance may cause some aerodynamic changes, I really doubt that at 80mph it would have that much aerodynamic force to cause the front wheels to wobble as if impallanced. What makes me think this specifically is not a factor is that while braking, the wobble is more pronounced, which is a result of a "down-vector" force being applied to the wheels. I'm not totaly discounting the aerodynamic issue, just that at 80mph, I doubt it can have that much effect on the wheels sticking out 12mm farther. If I'm wrong, I'd love to hear more or see some sort of aerodynamic data if it's out there.

For example, I wonder what speeds the front and rear spoilers like the GT spoiler starts to actually have some sort of down-force effet? I'm willing to bet it's much higher than 80mph though. Just a guess.
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      11-06-2011, 04:59 PM   #25
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Wheel balance issues!

I dont care about any of the tech talk here! I have had the same situation with slightly older car! BOTTOM LINE, your wheels need to be zeroed out. Forget about low numbers. I had my wheels balanced by the same people 4 times with no resolve then two time with another shop. At the third shop they told me that the wheels were not zeroed out and with fifteen minutes of work the cars vibration was gone and it felt like bone stock again. Dont let those over jealous jerks screw with your mind bro! KEEP GETTING THEM BALANCED BY DIFFERENT SHOPS UNTIL YOU FIND A SHOP THAT HAS A MACHINE THAT IS PERFECT AND YOUR ISSUE WILL BE GONE.

Good luck!
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      11-06-2011, 09:00 PM   #26
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Originally Posted by dvmarks13 View Post
I dont care about any of the tech talk here! I have had the same situation with slightly older car! BOTTOM LINE, your wheels need to be zeroed out. Forget about low numbers. I had my wheels balanced by the same people 4 times with no resolve then two time with another shop. At the third shop they told me that the wheels were not zeroed out and with fifteen minutes of work the cars vibration was gone and it felt like bone stock again. Dont let those over jealous jerks screw with your mind bro! KEEP GETTING THEM BALANCED BY DIFFERENT SHOPS UNTIL YOU FIND A SHOP THAT HAS A MACHINE THAT IS PERFECT AND YOUR ISSUE WILL BE GONE.

Good luck!
Thanks for the input... can you be specific about what it means to "zero out wheels"? how do you exactly do that? who finally was able to do your balance? national large chain tire shop, dealer, specialty shop??

thanks again
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