Windshields for motorcycles are made from either polycarbonate (Lexan) or acrylic (Plexiglas). Each type of plastic has advantages and disadvantages.
Polycarbonate is an extremely strong plastic. Polycarbonate is about as transparent as glass. Polycarbonate cuts and forms easily at both room temperature and at higher temperatures. For machining purposes, you can work with polycarbonate pretty much the same as you would aluminum. Polycarbonate has a major drawback for windshield use: polycarbonate picks up water from the air. The water eventually makes the polycarbonate cloudy. This water will form bubbles if you heat the polycarbonate to forming temperatures. So, before you can form polycarbonate, first you have to place it in a drying oven at about 200° for about 12 hours. Because of this, only companies that manufacture polycarbonate make windshields. Polycarbonate is sensitive to ammonia, so glass cleaners like Windex should not be used on polycarbonate. Polycarbonate windshields need a coating to protect them from chemicals and prevent them from absorbing water from the air. This optical coating is difficult to apply uniformly, resulting in optical distortion. It also scratches and cannot be repaired with plastic polish.
Acrylic is only about 3% as impact resistant as polycarbonate. Normal acrylic shatters upon impact, and therefore is considered an unsafe material for windshields. Acrylic is very chemically resistant, and is more transparent than glass – glass absorbs about half again as much light as acrylic does. Acrylic forms easily at high temperatures, about 300°. However, machining acrylic at room temperature is difficult. It’s not very easy to cut acrylic with a saw or drill holes in acrylic without shattering or weakening the material.
Polycarbonate is a DOT approved material for making windshields; normal acrylic is not. Some states require DOT approved windshields, and therefore in these states a normal acrylic windshield is actually illegal, however these laws are rarely enforced. Normal acrylic can be shattered by an impact from a rock moving at speeds as low as 15mph.
A special high cost acrylic called Impact Modified Acrylic is available. This form of acrylic is DOT approved for windshields. We use only DOT certified impact resistant plastics to make Calsci windshields. Our windshields will not shatter if hit by a rock. We test our windshields by shooting them with a .22 caliber rifle and verifying that the windshield maintains its basic integrity without shedding small pieces that could impact your face or eyes. No windshield can protect you against everything, but we do our best to make certain that our windshields protect you against the small rocks frequently thrown up by other vehicle’s tires.
Even though Calsci windshields are designed so that you look over them, not through them, we use only optically correct shapes that will not distort your vision if you do look through the shield. If you look through one of our shields at a dividing line on the highway, you’ll see essentially no bending of the straight line. You’ll never get a headache from looking through one of our shields.
Nearly all of our windshields have vents. These vents are part of the aerodynamic design of the shield, to reduce turbulence and noise. They are not there to make a flow of air on the rider. When you’re riding on the highway, any windshield is pushing air away from the rider. This leaves a low-pressure pocket between the windshield and the rider. The air flowing past the motorcycle wants to drop into this low pressure area. If the outside air is allowed to spill into the area between the windshield and the rider, the result is turbulence, noise, and drafts. When outside air spills into the rider area, it almost always falls in a curved path, causing spinning vortices of air. These vortices are noisy and can cause the battering and hammering on your helmet reported by some riders. Our windshields and vents are designed to funnel air into the rider region to relieve this low pressure area and greatly reduce the tendency of outside air to spill in. The vents are designed so that the air coming through them is quickly dispersed, leaving almost no detectable air flow at the rider. Our goal is to produce almost completely still air on the rider with no back pressure.
Windshields with reverse flips and non-fair shapes will often generate semi-periodic chaotic swirls of turbulent air, called Von Karman vortices, after Theodore Von Karman. These vortices, or pockets of turbulence, grow as they move away from your windshield. If you feel your head being rocked or even slammed side to side or front to back as you ride, this is Von Karman vortices at work. Some manufacturers, to my own astonishment, actually claim to produce these vortices on purpose, apparently with the idea that some turbulence is “good” and will somehow perhaps cancel out the “bad turbulence.” We work very hard with the design of the shape of our windshields and the location and size of the vents to eliminate all Von Karman vortices.
Von Karman Vortices – the source of countless headaches.
Theodore Von Karman emmigrated from his native Hungary to the US in 1930 to become the director of the aerodynamics laboratory at Caltech. Mark of Calsci learned his aerodynamics in Von Karman labs at Caltech. Calsci windshields are designed using aerodynamic engineering principles that guarantee our shields do not generate turbulence. These are the same shapes that minimize drag and maximize fuel mileage.
All our shields are laid out on a computer and cut with an industrial cutting laser. Our shields are symmetric to within a thousandth of an inch (.025mm). All mounting holes are also drilled with the laser, guarantying an excellent fit to your bike. This precision is necessary to be certain your riding experience will be precisely the same as all our other customers, and precisely what we engineered for your bike.
Calsci windshields are designed by Mark Lawrence and Carl Porter. Carl has a Bachelor’s degree and a Master’s degree in engineering from Ohio State University. Mark has a Bachelor’s degree in engineering from the California Institute of Technology, and is currently working on a PhD in physics at the University of Southern California. Mark has a bit more than 500,000 miles of motorcycle experience. It takes about 6 weeks, eight to twelve prototypes, and typically several thousand miles to finalize a windshield design. Calsci windshields are not just a stock windshield made a bit wider and taller. We build and modify our prototypes until the resulting windshield is quiet, comfortable, and attractive.