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.
Typically, in a neutral chassis with double wishbone suspension up front where suspension geometry upon compression is more "predictable," that would be the case.
However, the MacPherson strut design up front actually behaves unpredictably with addition of swaybars up front, especially if the swaybars manage to reduce the "reduced camber" effect when there's too much compression. I've seen cases where additional front stiffness actually ADDED front end grip and alleviated understeer on a BMW. However, that is in combination with a ton of negative camber up front already and a moderately stiff front suspension setup without the ability to independently adjust compression. On a stock-ish suspension, I suspect if you can get up to 2.5-3º of negative camber, adding swaybar up front only may actually IMPROVE the front end grip on an M3.
But not on a car with mostly stock front camber.