Bike Racks - Drag?

[Willy Nilly]

I've seen a few bicycles on cars today being carted from one place to the next. Some are on racks on the back of the car and some on the roof. Would I be correct in assuming that this causes a load of drag quite a bit more fuel?

The ones on the roof always look like a decent side wind would have them off, breaking the car in the process.

[GroundEffect]

They probably double the drag of the car.

Even worse when the bike wheels are turning

[A900ss]

I reckon my fuel consumption increases by 25% when I have four bikes on the roof. That is motorway speed.

A and B road speed may see circa 15% increase.

Still the best place for transporting bikes in my opinion though