Driving a convertible can be a fantastic experience, but the effect of the differing wind pressure caused by the fast moving air passing over the car can cause unpleasant turbulence inside the car as the wind speed increases.
When driving with the roof down low pressure forms inside the car, pressure builds up outside the car as the speed increases. As the high and low pressures try to equalise, turbulence forms. A well designed wind deflector reduces and controls the turbulence by disrupting this process.
The design and materials used to disrupt the turbulent air must be carefully considered. Any attempt to 'stop' rather than disrupt the equalisation process can create turbulence elsewhere.
Deflectors made from solid materials (as opposed to mesh) in an attempt to 'seal' the cabin to prevent drafts from the rear can work well at low speed (30mph or less). As speed increases the equalisation process kicks in, often causing the air to 'eddy' over the driver/ passengers' heads. As speed increases so too does the pressure on the wind deflector structure.
A poorly designed deflector will detract from your driving pleasure, increase fuel consumption and in extreme cases damage your car.
A well designed wind deflector can be a real asset for roof-down driving. SVA deflectors create a 'pleasant' effect by stabilising air flow inside the cab at speed. Using an SVA deflector the occupants can adjust the air flow inside the cab by simply opening or closing the side windows.