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Old 06-10-2009, 07:40 PM   #1
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Join Date: Jun 2009
Location: NoVA
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My Ride: '01 325i
Another Cupping Question (sorry...)

Ok - So this is my first post.. I have been lurking and researching but never posted.. (special thanks for the DIY for Rotors / Pads and valve cover gasket!)

I have an 01 325i, sport package. About 15k miles ago (about 75k) I replaced all 4 tires with Pirelli p6's, now all 4 tires are cupped on the inside, as you can imagine, horrible noise.

The alignment "seems" to be ok, there is no pulling and on an open road, car keeps straight. braking is fine..

I ordered the P6's from delivered to a local bmw (German Car Specialist) mechanic and had them mounted. He also replaced the bushings on the front at that time. He does not have an alignment rack so he took it to the neighboring car care place for the alignment..

I have since taken it to another mechanic who mentioned that the wheels may be bent....

Any ideas about what could be causing this?? My neighbor with a 99 328i said he had the same issue with nero zero's and had a rear bearing replaced as well as tires and alignment..

Thanks in advance for any advice!

Last edited by shardt; 06-10-2009 at 07:41 PM. Reason: edit
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Old 06-10-2009, 08:25 PM   #2
Penguin Koolaid
Join Date: Feb 2004
Location: Chitown
Posts: 6,701
My Ride: Inline Six
Dial in more positive camber and decrease the toe in a bit. The stock sports suspension has enough negative camber to create cupping, especially with softer tires.
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Old 06-13-2009, 03:38 PM   #3
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Join Date: Apr 2007
Location: So Cal - 310
Posts: 991
My Ride: 04 330Ci ZHP
If they're truly cupped, the first most likely culprit is worn shocks/struts.

When the shock wears out, it's ability to dampen the bouncy action of the spring is lessened. If the shock is completely toast, this manifests itself as the chassis bouncing up and down. However, the shock wear is progressive and a long time before it's so weak that the car bounces all over the place, the shock loses it's ability to keep the car's weight steady and even on the wheel.

So what happens is there's a constant, rhythmic fluctuation in the pressure in the contact patch. At the edge of the tire, both because of camber and because of the load on the edges when the car turns, this fluttering in the pressure causes uneven wear that we call cupping. The leading edge of the tread block will be worn down more than the trailing edge.

At 75,000 miles, it's possible that your shocks and struts are done.

The thing that makes me wary of diagnosing your problem as shocks/struts is that usually you'll get this wear on 1 or 2 corners first and you mention it happening on all 4 at once. That's kinda funky. So it may be that PK is correct about the alignment settings.

A good mechanic is the only one that can give you a definitive answer, but hopefully this info helps.

When you get it figured out, come back and post the resolution to assist future readers with similar issues.
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