From what i got of it...
The anti roll bar has a bend in it just before the wheel arch to up and over the tracking arm i think it is.. and basically onthe uprated ones the bend is longer to isnt so close, but on the standard ones its close tight bedn around it, so when you full lock and bias the weight of the car forward, on standard ARB's it will do a knocking sound, as the ARB touches the tracking arm. This doesnt happen on the uprated ones as the bars are thicker the bar can not be bend that tight to the tracking arm so therefore the bar doesnt hit it....
Correct me if I'm wrong anyone...