[SimHacker]

I've found that pie menus with four different directions are quite reliable (see the description I posted here of the ConnectedTV palm app, which supported buttons with four different stroke directions plus tap). Eight different directions work well with a mouse or big touch screen, in situations where you can afford to give the screen some visual attention and the consequences of making a mistake aren't deadly, but I believe four directions are reliable enough for automotive applications, as long as you require enough motion to get enough "leverage" and give decent feedback.