Cargo racks on your van’s roof generate noise as a result of the interaction between the airflow and the profiles of the roof rack. Cross bars in particular generate a series of overlapping vortices known as a “Karman vortex street” after the scientist who discovered the phenomenon in 1911.  When a roundish body is invested by a fluid flow – in our case when the cross bars of a roof rack are invested by an air flow – a wake of vortices (a “vortex street”) forms. This causes the air pressure around the body to fluctuate, generating vibration and noise when the air flow reaches a certain speed.  The phenomenon is amplified by the passage of air between the cross bar and the van roof. Air passing through this gap is compressed and accelerated, increasing vibration and noise inside the vehicle.  Syncro System engineers have finally developed a solution to this problem. The ULTRASILENT ridged profile is designed for application underneath the first cross bar in the roof rack and prevents or dramatically reduces the formation of vortices along with the noise that accompanies them.  The ridges on the underside of the profile break up the air flow that passes between the cross bar and the roof without interfering in any way with the normal use of the roof rack. The result is a dramatic reduction in vortex formation and therefore in perceived noise. The new profile is extremely light and is positioned where it does not take up useful space or interfere with the use of ropes and straps to secure cargo.  Remember that even before this latest innovation, Syncro roof racks were very silent thanks to the ULTRASILENT profile of the aluminium cross bars. Now, with the addition of this new noise-reducing ridged profile, noise has been reduced by a further 50%, allowing you to enjoy a quieter drive even at motorway speeds and above.  Yet another success for the Syncro engineering team who, since 1996, have been developing new ways to make van users’ work more efficient and more enjoyable too!