What Tim is saying is that our E46 already has a tendency to understeer from the factory setup. Reason being studies have shown that drivers (regular not race/track) tend to have more time to react in an understeering situation.
Adding a stiffer front bar will induce even more understeer. Hence, the ideal approach is to stiffen up the rear bar while leaving the front as it is, until you find a neutral handling setup. Ideal that is.
Also, bear in mind that a thicker bar do not necessarrily imply a stiffer setup. The material of the bar has to be taken into account. Afterall, different material has different stress/strain properties. Note that some bars are hollow as well.
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