Windshields serve a variety of purposes, including warding off -- you guessed it -- the wind on chilly nights and directing the airflow around the driver to minimize aerodynamic drag. In the summer, a shorter windshield can direct some of the breeze onto the rider so he doesn't cook in the still air. There are also adjustable windshields that mount on a set of movable brackets, allowing the rider to change the angle manually [source: MadStad Engineering]. Some motorcycles allow adjusting the windshield with a push of a button on the handlebars.
In addition, Honda Goldwing motorcycle owners can choose to install Air Wings, a set of adjustable fins that are mounted on either side of the bike, to increase or decrease airflow as desired. The fins can also be angled to deflect heat from the motorcycle's engine and radiator [source: Baker Built Air Wings Inc.].