Aerodynamics

Behind the car.
Not on top of it.

A roof box lifts your load up into the fastest, cleanest air the car meets. SKiiBOX sits on the tow hitch instead — inside the pocket of already-disturbed air the car drags along behind it anyway.

Roof box on roof bars 12
  • 1Roof bars lift the box about half a metre above the roof, so the frontal area grows.
  • 2The flow separates behind the box into a large, unsteady wake.

Typical roof box: 205 cm long, 42 cm tall, raised on roof bars.

SKiiBOX on the tow hitch 12
  • 1Nothing goes above the roofline, so the frontal area is unchanged.
  • 2The box sits inside the wake the car already leaves behind it.

SKIIBOX 200: 203.5 cm wide, but only 51.5 cm deep and 43 cm tall in the direction of travel.

Undisturbed flow → strongly disturbed, turbulent flow Illustration of the flow principle — not a CFD simulation

Why placement matters more than shape

Aerodynamic drag comes down to two things: how much frontal area the car has to push through the air, and how much disturbed air it leaves behind.

A roof box makes both worse. Roof bars lift it roughly half a metre above the roof, straight into the fastest, most undisturbed airflow around the vehicle. Behind it the flow separates into a large, unsteady wake the car tows along for the whole trip.

Behind the car, that wake already exists. The air back there is disturbed whether you carry anything or not — so a box that tucks into it has far less air to push out of the way. SKiiBOX is built around exactly that: wide enough to take skis across the car, but only 51.5 cm deep and 43 cm tall in the direction you are driving.

Sources: NAF & Motor — roof box electricity consumption test (2022) · Sandberg, M., Aerodynamic study of vehicle mounted cargo boxes, Chalmers University of Technology (2022).