[rattlsnak]

Worn tires absolutely affects the alignment settings. Your car is not sitting straight/properly/correctly if they are worn. Think of it like getting it done if the car was sitting on a cobblestone road or some kind of unlevel surface.. Yes most alignment machines hook to the wheel/rims but if that rim is leaning one way of the other because of the tire that is mounted to it, then when the alignment is done, it will be set to that incorrect setting and when the new tires go on, your alignment is off again...