Window deflector

Deflectors can be supplied as official accessories, generally branded, or as third-party components.^[3] They are plastic elements of various shapes and sizes that can be installed in a fixed, movable or adjustable way depending on the type of application.

Openings of passenger compartments, such as windows, sunroofs and some convertible roof systems, when fitted with air deflectors provide improved comfort thanks to noise reduction of up to 11–12 decibels with windows open and 5 decibels with windows closed.^[4] Moreover, according to experimental tests performed on scaled models, lateral deflectors such as those applied to the window frame allow a reduction of the aerodynamic drag coefficient by 4–6%.^[5]

In vehicles with overhangs, such as some articulated trucks or trucks with tall cargo bodies, the air deflector may be present on the top of the cab (possibly of the collapsible type to adapt to different overhangs, but also for driving without a semi-trailer) or also on the sides; it improves the shape factor and reduces aerodynamic drag (impact with air), especially at high speed, making it possible to reduce fuel consumption.^[6][7][8]

Deflectors designed for windows allow air exchange without weather elements (rain, wind or sun) entering the vehicle, as well as preventing the windows from fogging up on rainy or hot days. In most cases they are appendages external to the passenger compartment, but some internal versions also exist, such as in the Lancia Fulvia of the 1960s. In the latter case the deflector is not placed in the front and upper part of the window but in the rear and upper part. Some of these systems also extend to a second element placed on the rear windows, mainly to provide protection from rain.

The air deflector was also used in competitive motorsport, as in the case of the Alfa Romeo 155 V6 TI, which introduced the solution disguising it as an accessory rear-view mirror.^[9] Other sports vehicles that have used air deflectors include the Alfa Romeo 75 "Turbo Evoluzione".

Sunroofs with different air deflector solutions

An air deflector is also applied to other components that connect the passenger compartment with the outside, such as the sunroof, which may be equipped with an automatic system that causes the anti-turbulence deflector to rise when the roof is opened, since the glass no longer exerting force on the lever system allows the springs to lift the deflector.

With regard to vehicles with convertible roofs, a wind blocker is generally used, which consists of a vertical mesh element (similar to coarse fabric mesh) positioned behind the headrests of the driver and front passenger seats. This element may be combined with or composed of a second horizontal element covering the rear part of the passenger compartment. However, there are also solutions based on deflectors (which may assume various shapes and designs), as in the case of the Ferrari Roma Spider, where the deflector partially closes the rear part of the passenger compartment (losing the possibility of using the rear seats) and prevents air from entering the lower part of the compartment.^[10]

The use of air deflectors is widely employed in commercial vehicles, particularly on tractors, especially when fitted with semi-trailers. Their use is also present on trucks equipped with cargo compartments higher than the cab. The use of an air deflector allows reduction of aerodynamic drag, particularly at high speed, enabling lower transport costs because fuel consumption is reduced, which also allows a reduction in pollutant emissions.^[11]
In some cases their use is also extended to the rear part of the trailer or cargo compartment, allowing further improvement in aerodynamic performance.^[12]

Based on the way wind deflectors are installed, they may be classified as follows:

• Vehicle window
• Side skirt
• Recreational vehicle