Depending on your driving conditions, most windshield wipers provide good performance for a few months, and wear out within a year of use. Some factors that will age the metal and rubber in your wipers:

• Airborne enemies – Like many parts of your vehicle, windshield wipers can be degraded over time from exposure to engine exhaust, acid rain, and salt (from sea air or winter road de-icing).
• Ultraviolet light (UV) – UV exposure can stiffen, crack, and degrade rubber. A stiff or brittle rubber edge will not maintain smooth, quiet contact with your curved windshield.
• Temperature changes – Rubber contracts in hot weather and becomes brittle in cold weather.
• Time – Even in perfect conditions, rubber quality deteriorates over time.

Here are some best practices to keep your windshield wipers working better, longer:

• Keep your wipers clean. Clean your windshield wiper blades once a month with rubbing alcohol. You can also try running sandpaper over minor imperfections in the rubber, but once they’re damaged enough to leave streaks, replace them.
• Keep your windshield clean. Wash your windshield regularly, and always remove any visible dirt or debris before driving. Operating your wipers over an uneven surface can ruin the rubber edge. The wipers will leave streaks on your windshield until you replace them. (For the same reason, never use your wipers to help de-ice the windshield. An icy windshield is a very uneven surface.)
• Don’t make your wipers work too hard. Always clear your windshield and wipers of accumulated snow, slush, and ice before starting your vehicle. Forcing your wipers to push against extra weight can bend the blade assembly. (For the same reason, consider dedicated winter wipers if you live where it snows. Their design encourages snow and ice to slide off your wipers instead of accumulating between the metal parts. And they’re made of rubber formulated to stay supple in colder weather.)
  
  • Tip: Prevent snow and ice accumulation by lifting your wipers away from your windshield when snow or ice is in the weather forecast. This also prevents your wipers from freezing to the glass.
• Slow down rubber breakdown. Keep your vehicle in a climate-controlled shelter as much as possible. Very hot and cold temperatures can weaken the rubber wiper blades. Failing that, park in the shade whenever possible to avoid UV exposure.

Windshield wipers should be inspected at least every six months and replaced at least once a year. (Getting new wipers twice a year allows you to take advantage of dedicated winter wipers.) Between inspections, clean your wiper blades with rubbing alcohol once a month.

You can replace windshield wipers at any time, but here are two reasons to make the change in spring and fall:

• Hot summers and cold winters both take a toll on the rubber in your wiper blades. Replacing them in spring and fall lets you face each extreme with a fresh set of wipers.
• Installing new wipers in spring and fall lets you take advantage of winter wipers for the colder months. Winter windshield wipers feature a rubber shield over the blade assembly to prevent ice and snow from accumulating in the metal frame.

If both wipers were installed together, they should be replaced together because they’re wearing out at roughly the same pace. Even if one wiper appears to be in better shape, its rubber has endured the same temperature changes and driving conditions as its twin. It’ll probably show visible wear soon. And who wants to keep track of different replacement cycles for each wiper?