The best roof cargo bags

The car-clip system is the point

Most rooftop cargo solutions assume you have crossbars. Plenty of cars do not, and fitting them costs more than the bag does.

Rightline's answer is a set of clips on the ends of the straps that hook into the door frame weather molding. You open the doors, hook the clips inside the frame, close the doors, and the straps are anchored to the car's structure rather than to a rack.

It works. The trade-off is one that nobody mentions in the listing: the straps now run through the door openings, so every time you open a door you are opening it past a strap, and on a four-door car that is four doors. For a road trip it is fine. For daily use it is an irritation that gets old quickly.

Waterproof and weatherproof are different words

This is the specification difference between the two Rightline bags and it is the reason for the ranking.

The Sport 2 is described as waterproof with a waterproof zipper. The Range 2 is described as weatherproof. In practice the difference shows up at the closure: a zipper is the obvious water path on any bag, and a bag that is sealed everywhere except its opening is a bag that leaks at its opening.

Neither publishes a load rating in pounds, only volume. That is a real gap on a product whose weight is the thing your roof cares about, and it means the constraining number has to come from your car's manual rather than from the bag.

The aerodynamic cost is real

A roof bag is a large, blunt object in the airflow above the most aerodynamically sensitive part of the car. Drag rises with the square of speed, so the penalty is modest around town and substantial at highway speed — which is exactly where road trips happen.

We are not going to invent a percentage, because it depends entirely on the vehicle, the bag and how fast you drive. What is worth planning for is that a long highway trip with a loaded roof bag will cost you noticeably more fuel than the same trip without one, and that driving a little slower recovers a disproportionate amount of it.

Two practical consequences: mount the bag as far forward as the roof allows so the windshield deflects air over it rather than into it, and take it off when you are not using it. A bag left on the roof between trips is a permanent fuel penalty for nothing.

Packing, which decides whether it survives

• Fill it completely. A partly-full bag flaps, and flapping is what destroys fabric and works straps loose. Pad out the space with soft items
• Soft things only. Bags, bedding, clothes. Anything with a hard corner works against the fabric from the inside for the whole journey
• Heavy at the bottom and centred. Weight high and to one side changes how the car handles more than people expect
• Protect the paint. A blanket or a mat under the bag stops grit trapped underneath from sanding the roof at every vibration
• Re-check the straps after twenty minutes of driving, and at every stop. Loads settle

Cheaper answers that are often better

A roof bag is the right answer when you genuinely need more volume than the car has. It is the wrong answer when the real problem is that the space you have is badly used.

Before adding 15 cubic feet to the roof, it is worth being honest about the trunk. A cargo net or a set of tie-downs stops things sliding and lets you stack properly rather than spreading out — see cargo nets and tie-downs. A trunk organizer does the same job with structure, covered in best trunk organizers.

And if the load is dirty or wet — camping gear, sports kit, garden waste — a cargo liner in the trunk may solve the problem you actually have, which is not space but mess. That is best cargo liners.