Originally Posted by Porschefile
Someone feel free to correct me if I'm wrong here, but I think stiffer front bars cause more understeer and stiffer rear bars cause less understeer (more oversteer). I wouldn't add a front bar only, because I don't want more understeer. Sways are a fine tuning device anyway, they don't make an ill-handling car handle properly or vice versa.
I have no experience with sway bars on the e9x M3 but the e46 M3 really likes a stiffer front sway bar (relative to the rear) because it greatly improved/controlled the camber curve - stiffer bar actually reduced understeer (obviously there's an upper limit). I believe the e9x has a better camber curve and it this shows up in static camber settings - e46 requires a lot of front camber (more than neg 3-3.5 deg if using r-comps) whereas the e9x does not.
As for the Dinan front bar I think it is designed to work with their spring kit so not sure what effect - over or under steer - it would have on the handling characteristics of a stock e9x suspension?