When you lower the rear suspension (as I suspect he has) the panhard rod is no longer level - or at least nearly level - under a normal load. It will slope downward from the axle to the body mount by an amount equal to the lowering. This will impart some up or down forces when the sideways loads are vectored though that angle.

Nice auto-X car. I like 2002's, but they are all rusty beyond belief here in the midwest. Nice lightweight sheetmetal didn't mesh well with salty roads. What sort of motor is going in there? E30 M3? That would be sweet.

Many, many years ago I test drove a 'Turbo 2002'. At the time I didn't know BMW had actually produced them, or I would have scrutinized it closer seeing if it was genuine. The odds are rather low, but from what I recall this was a pretty good imitation. Had flares of the right type, the underhood stuff was pretty tidy and didn't really look home-built. It was a hoot to drive. Step on the gas and for about a 2-count not much would happen other than the increasing whine from under the hood. Then the rear end would squat and it would take off like a rocket. I think a smaller turbo would have worked wonders. However, the tatty appearance and suspect engineering combined with the asking price kept me away from it, I got a lightly used '83 318i instead.
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I'm JohnMc, and I approved this message.