Car Drag Formula Varies with Speed?

Hi,

I've read in a website that the drag (air resistance) formula for a car would be different:

-> for velocities under 86 km/h
Drag = K(coefficient) * V

-> for velocities over 86 km/h and under 1200 km/h
Drag = K(coefficient) * V^2


I've researched a little bit and only one formula is generically used to describe drag, the one that considers V^2:

D = 1/2.p.V^2.C.A

D-drag
p-density of fluid
C-drag coefficient
A-area

I understand that this is only one of the accepted representations, and that it is only applicable under certain conditions. Nevertheless, I am looking to understand very simplistic if the claim that under roughly 86km/h we should use only V, and after 86km/h we should use V^2 is valid.

The truth is that I'm finding it a little bit difficult to understand why the formula would change from 86 km/h onwards. The only reason I can conceive the formula to change would be empirical/experimental testing. But even so, what could happen at roughly 86 km/s to suddenly change the drag formula to consider V^2 instead of V? Is this some sort of mystery?

* I've also heard about the velocity being 100km/s or 60mph, instead of 86 km/h, but again, I would just like to understand if the formula changes and why would that be.

Thanks