Similar to the Auto Rucksack, the Rightline Cargo Saddlebag takes your cargo off the roof and throws it on the rear-end of your car. Unlike the Auto Rucksack, a pack aimed at small cars, the Cargo Saddlebag is designed for larger vehicles like SUVs, minivans and crossovers. It's basically a backpack for your vehicle, that hauls all sorts of gear and toys.

Unless you have millions of dollars to spend on a supercar with purpose-built aero box, chances are you're going to opt for a clunky, non-aerodynamic roof box or luggage bag that eats away at your car's efficiency. According to Rightline, you can get an extra 5 miles (8 km) out of every gallon (3.8 liters) of gas, by sliding your gear from the roof to the back of the vehicle – where it won't impede airflow. Two adjustable straps lash the Cargo Saddlebag to your roof rack, while two lower straps secure it to the bumper or tow hitch. A fifth strap can be used to wrap the perimeter tighter. A sleeve on the outside of the bag lets you easily remount your license plate.

Not only is the Cargo Saddlebag more aerodynamic, but its rear-mounted design makes it easier to load and unload. The bag is low enough that you can easily unzip it to access your gear. It has two carry handles, so you can take the entire thing off and haul it wherever you're going.

The Cargo Saddlebag holds up to 14 cu ft (396 liters) and 100 lbs (45.5 kg) of gear. Its Hydrotuff material has a waterproof PVC lining and tough 600D polyester shell. To ensure that your gear stays dry, Rightline also offers a waterproof liner. Of course, the bag's soft shell won't protect from hard hits like a plastic cargo box, so be sure that you don't stop short while someone's tailgating you.

The Cargo Saddlebag retails for US$140, which is cheaper than the average rooftop cargo box and competitive with rooftop bags.

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