Interesting question
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As I understand it, bump steer is a product of the disparity
between steering arm and suspension arm geometry. Therefore, the only way that
the arm itself could affect bump steer would be if the relative positions of the centre
of the inner fixing bolt and the ball joint pivot centre were changed. If the arms have
the same centre distance as a stock AE86 LCA, this is not the issue.
Looking at your pic I would not be certain that those arms are made from OEM AE86
arms. So the attachment point for the tension rods could be different, and this might
have changed your caster angle ? I don't know if caster affects bump steer, so maybe
not an issue either.
Cheers... jondee86