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, Wed, 31 May 2006 21:17:10
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I don’t think anyone on the BB has made this distinction before. True cupping is generally related to the tire not making even contact with the road surface. I suspect that once the suspension geometry reaches a certain position, the dampers cannot keep the wheels firmly on the ground due to either the dampers being weak against the load, odd geometry, or some combination. [I haven’t calculated it, but I would guess that a damper and the entire suspension for that matter would have to be pretty beefy to handle the dynamic loads of a fully loaded 9-5 at speed, being driven hard, fighting the negative camber angles which are already worsened by the loaded static condition.] The wheel is also out of balance as it rotates off its center axis. Since the camber is negative on the rear of the 9-5, the tires cup on the inner edge of the tire. If the alignment is correct and the suspension is new, there is a nominal amount of inner edge wear that can be dealt with by regular rotation. The cupping that I think most people are referring too cannot be avoided by regular rotation (I guess it could if you rotated very frequently and never loaded the car up.). Certainly I know mine couldn’t have because about 3K after a rotation a perfectly good tire rotated from the front was not only cupped, but the inner edge was worn right off the tire (hence the blowout). In a loaded state tires are far more prone to cupping. I think some companies make elaborate active wheel balance devices for semi tractors.
Others have suggested that the inner wear pattern is toe related. I don’t see how this can be. Too much toe means the tires would be dragging slightly as you drive and would get scrubbed into a sawtooth wear pattern. The inner edge wear I have seen is where the tire surface is smooth, but the inner shoulder is either worn more than the center and outer shoulder or worn more and cupped.
posted by 69.113.12...
, Wed, 31 May 2006 21:17:10
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