When should struts be replaced on 2002 Hyundai accent gl 4 door sedan?

You know when to change the struts when you are driving down the road and you hit a bump and get whip-lash. But really all you have to do is peek up under the wheel well and see if they look alright. If they are falling apart then you need to replace them...or if your car sounds like a sqeaky matress you need to go in and have them checked