Craig - Usually front arm sweep will increase steering responce getting the car into the corner better - Sometimes it will make the car "twitchy" or hard to drive on the straights if you have too much. Usually though, once the car has set into the corner, I think it actually makes the car understeer a little more than straight pins. I've never been a big fan of this so I usually run only a small amount where EJ runs more than I do (always) but complains at times about his car going straight...lol...
