The Thule Motion XT XL is a hard-shell roof cargo box designed to mount on top of your vehicle

The Thule Motion XT XL is one of the largest roof-mounted cargo boxes on the market, built to hold luggage, sports equipment, or other gear on top of your car, truck, or SUV. It's a hard plastic shell that clamps to a roof rack system and opens from the side, giving you access to the storage space without having to unload from the top down. The XL version is the biggest in Thule's Motion XT line, holding roughly 18.7 cubic feet of cargo — enough for multiple large suitcases or a combination of smaller items.

The box itself weighs around 75 pounds empty, so installation requires either two people or a roof rack rated to handle the combined weight of the box and its contents. It comes with mounting hardware and a key lock, so you can find your belongings while parked. The shell is aerodynamic, meaning it's designed to reduce wind noise and fuel consumption drag compared to older, boxier roof boxes.

Key Takeaways

  • The Motion XT XL holds 18.7 cubic feet and weighs 75 pounds empty, so your roof rack must be rated for the total load.
  • Installation requires a roof rack system with crossbars, and you'll need to may support your vehicle's roof can support the weight before mounting.
  • The box opens from the side, not the top, which makes loading and unloading easier than traditional roof boxes.
  • Thule includes a key lock and mounting hardware, but you may need to purchase an adapter if your roof rack uses a non-standard attachment system.
  • Fuel economy typically decreases by 5 to 10 percent when a roof box is installed and loaded, depending on highway speed and box design.

Roof Rack Requirements and Weight Limits

Before you buy a Motion XT XL, you need to know your vehicle's roof weight capacity and whether you already have a roof rack installed. Your vehicle's owner manual lists the maximum roof load — this is the total weight your roof can safely support, including the box, crossbars, and everything inside. The Motion XT XL empty weighs 75 pounds, so if you plan to load it with 100 pounds of cargo, your roof rack system needs to be rated for at least 175 pounds, plus the weight of the crossbars themselves.

Most modern vehicles have a roof capacity between 75 and 150 pounds, though some larger SUVs and trucks can handle 200 pounds or more. If your vehicle doesn't have a roof rack, you'll need to purchase one separately — Thule makes racks for most vehicle models, but prices and compatibility vary. Check your vehicle's manual or contact the dealership to confirm your roof capacity before ordering the box.

Exceeding your roof's weight limit can damage the roof structure, void your warranty, and create a safety hazard at highway speeds. If your roof capacity is borderline, consider a smaller cargo box or using a hitch-mounted cargo carrier instead, which transfers weight to the frame rather than the roof.

How the Side-Opening Design Works

Unlike older roof boxes that open from the top, the Motion XT XL opens from the side, which changes how you load and unload. The lid swings open perpendicular to the vehicle, so you don't have to reach up and over the top of the box to access items at the back. This design is especially useful in tight parking spaces or garages where you can't open a top-hinged lid all the way.

The side-opening mechanism uses a gas strut (a spring-loaded arm) to hold the lid open while you're loading or unloading, so you don't have to prop it up manually. The hinge is sealed to keep water and debris out of the cargo area. When closed, the lid locks with a key, and the seal is designed to be weatherproof, though no roof box is completely waterproof — condensation can form inside during temperature changes, so it's wise to avoid storing items that are sensitive to moisture for long periods.

Installation Steps and Tools You'll Need

Installation typically takes 30 to 60 minutes with two people and basic tools. You'll need a socket wrench or adjustable wrench to tighten the mounting clamps, and the hardware is included in the box. Thule provides detailed instructions with diagrams, and video guides are available on Thule's website and YouTube.

The process involves positioning the box on your roof rack crossbars, aligning the mounting feet with the clamps, and tightening the bolts in a specific sequence to may support even pressure. Over-tightening can crack the box or damage the crossbars, so the instructions specify torque values — typically 15 to 20 foot-pounds. After installation, check the bolts after your first 100 miles of driving, as they can loosen slightly during initial use.

If your roof rack uses a non-standard attachment system (some older racks or certain vehicle brands), you may need to purchase an adapter kit separately. Thule sells these, but they add to the total cost and installation time. Before you order, confirm that your specific roof rack model is compatible with the Motion XT XL.

Fuel Economy and Wind Noise Impact

Adding a roof box increases aerodynamic drag, which reduces fuel economy. Studies and manufacturer data show that a loaded roof box typically decreases fuel economy by 5 to 10 percent on highway driving, with the impact varying based on vehicle shape, box design, speed, and load weight. A boxy SUV with a full roof box may see a larger drop than a streamlined sedan with a partially loaded box.

Wind noise also increases, especially at highway speeds above 60 miles per hour. The Motion XT XL is designed to be quieter than older, less aerodynamic boxes, but you'll still notice more road and wind sound than you would without it. Some drivers report that the noise becomes less noticeable after a few hours of driving, as they adjust to it.

If fuel economy is a concern, consider using the roof box only for longer trips and removing it when you don't need the extra storage. Thule boxes are designed to be removable — you can leave the crossbars on your roof rack and detach the box itself in under five minutes.

Maintenance, Cleaning, and Longevity

The Motion XT XL shell is made of durable plastic that resists UV damage and weathering, but it still requires occasional cleaning to prevent dirt buildup and maintain its appearance. Wash it with mild soap and water, and avoid abrasive scrubbers that can scratch the finish. The hinges and seals should be checked annually and cleaned of debris to may support smooth operation and a tight seal.

The mounting hardware should be inspected before each trip, especially if you remove and reinstall the box frequently. Bolts can loosen over time, and a loose box can rattle or shift at highway speeds. Thule recommends checking the bolts every few months if you leave the box installed year-round.

The box itself typically lasts 10 to 15 years with normal use, though the exact lifespan depends on climate, storage conditions, and how often you use it. Storing the box indoors during winter or when not in use extends its life. If you live in a region with harsh winters, salt, or intense sun, inspect the box more frequently for cracks or seal degradation.

Comparing the Motion XT XL to Other Roof Box Options

Thule makes several other roof boxes in different sizes and price ranges. The Motion XT (non-XL) holds 16 cubic feet and weighs about 65 pounds, making it a lighter option if your roof capacity is limited. The Thule Force XT is a different line with a more angular design and slightly different mounting system. Other brands like Yakima, Rhino-Rack, and Sportrack offer competing models at various price points.

The Motion XT XL is positioned as a premium option — it costs more than smaller boxes or budget alternatives, but the side-opening design, aerodynamic shape, and Thule's reputation for durability justify the price for many buyers. If you need maximum cargo space and don't mind the cost, the XL is the largest option in Thule's Motion line. If you want to save money or have a lower roof weight capacity, a smaller box or a hitch-mounted carrier may be a better fit.

Frequently Asked Questions

Can I install the Motion XT XL on a vehicle that doesn't have a roof rack?

No, you need a roof rack with crossbars to mount the box. If your vehicle doesn't have one, you'll need to purchase a rack system first. Thule makes racks for most vehicles, and installation typically takes 1 to 2 hours. Alternatively, consider a hitch-mounted cargo carrier if your vehicle has a trailer hitch.

Will the roof box fit in my garage?

The Motion XT XL is 79 inches long, 31 inches wide, and 16 inches tall when mounted on the roof. Measure your garage height and the clearance above your vehicle to confirm it fits. If your garage is too low, you can remove the box and store it separately, or park outside and remove it only when traveling.

Is the Motion XT XL waterproof?

The box is weather-resistant and designed to keep most water out, but it is not completely waterproof. Condensation can form inside during temperature changes, and water may seep in if seals are damaged or bolts loosen. Avoid storing items sensitive to moisture for extended periods, and inspect seals annually.

How much does the Motion XT XL cost?

Prices vary by retailer and region, typically ranging from $500 to $700 for the box alone. Roof rack systems cost an additional $200 to $500 depending on your vehicle. Check multiple retailers and compare prices, as sales and discounts are common.

Can I use the Motion XT XL on a rental car?

Most rental car agreements prohibit roof-mounted equipment because it requires drilling or clamping to the roof. Check your rental agreement or contact the rental company before attempting to install a roof box. Hitch-mounted carriers are sometimes permitted, but confirm first.