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[...]
In contrast our front suspensions have positive caster (7.3°), positive mechanical trail (24 mm) and negative scrub radius (-11 mm), all of which are typical for front suspensions. Positive caster and trail result in a self-aligning torque about the kingpin axis in response to cornering forces. This is why steering effort increases with increased cornering g and why the steering wheel will tend to center itself if released in a corner. Negative scrub radius results in a toe-in torque about the kingpin axis in response to braking forces. This is a stabilizing influence under braking when combined with the unavoidable compliances in the front suspension. All these characteristics are desirable in a front suspension.
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Just to make the quick point that, according to a 2006 BMW Tech training document I have found for the e9x non-M, it says the geometry is designed to have a small positive scrub radius of 6.1 mm with 34 mm offset wheels. If that is right, then with the stock 135 offset being 49 mm for 18" wheels (15 inward) the scrub radius would be negative 9 mm. With stock offset being 47 for the 17" wheel (13 inward) the scrub radius would be negative 7. This assumes the geometry of the e9x is otherwise the same as for the e82...
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Stay tuned!
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