The plural form is vortices btw.
Just one interesting thing to note about driving in convoy. Take 2 identical vehicles traveling in a convoy. As the distance varies between the vehicles, so does their Cd. At some point, as the trailing vehicle gets close enough, the Cd of the leading vehicle eventually gets lower than the trailing vehicle. Which means the leading vehicle can benefit more from drafting then the trailing vehicle. This makes total sense as we know most passenger vehicles need more aero help in the back than the front.
