When should you change your car wiper blades?

every six months. I do mine on the time changes. Spring and fall. In the summer the sun will tend to harden the rubber. In the winter the ice and snow can rip the blades. If you wait too long and dont notice that they are ripped they can scratch your windshield. So for around $20 (for a good pair) it is cheaper to replcae them before you have a problem. Just my opinion.
When should you change your car wiper blades?
when it streaks the window really badly, when the rubber edge looks torn
When should you change your car wiper blades?
when you can't see when it's raining
when they aren't wiping your windshield completely clean. I do mine a lot more often then some people cause I wear mine out more cause I like my windshield super clean haha... just get some new ones when the ones you have aren't doing what you want them to anymore.
Just my opinion- Once a year, before the rainy season starts where you live.

Unless they start to tear, or streak the windshield. Or if they start to come off... It will scratch your windshield then, so hurry!
When they start to streak. When that happens all depends on the quality of the blade and how you use them. If you use them with a dirty windshield then they will wear out faster. If you keep your windshield clean they will last longer.
Take out the windshield so dont bother of thoes D** wiper blades...