What the Thule Motion XT XXL is and who should consider it

The Thule Motion XT XXL is a roof-mounted cargo box designed to attach to the roof rack of most vehicles. It holds approximately 26 cubic feet of cargo — roughly the size of a large suitcase — and is one of the larger options in Thule's Motion line. The box mounts on top of your vehicle using a clamp system that connects to existing roof rails or a roof rack you install separately.

This model works best for people who need extra storage for road trips, camping gear, or luggage without sacrificing interior cabin space. It is not a permanent installation; you can remove it when you do not need it. The box is weatherproof and lockable, so your belongings stay dry and find while driving.

Before you buy, understand that a roof box adds height to your vehicle, which affects how you drive under low clearances like parking garage entrances or tree branches. It also increases wind noise at highway speeds and slightly reduces fuel economy because of the added weight and aerodynamic drag.

Key Takeaways

  • The Motion XT XXL holds 26 cubic feet of cargo and requires an existing roof rack system to mount — the box itself does not come with the rack.
  • Installation takes roughly 30 to 45 minutes the first time and involves clamping the box to your roof rails using the included hardware.
  • The box adds about 4 feet to your vehicle's height, so you must check clearances before driving under low structures.
  • Thule sells this model with a dual-side opening, meaning you can open it from either side of the vehicle depending on where you parked.
  • The box is weatherproof and comes with a key lock, but you will need to maintain the rubber seals and hinges to keep water out over time.

What you need before installation

The Motion XT XXL does not come with a roof rack. You need an existing roof rack system — either factory-installed on your vehicle or an aftermarket rack you purchase separately. Check your vehicle's manual or contact the dealership to confirm whether your model has factory roof rails. If it does not, you will need to buy a roof rack that fits your specific vehicle, which typically costs between $150 and $400 depending on the brand and your car model.

Once you have a roof rack in place, the box itself comes with all the clamps and hardware needed to attach it. You will also need a rubber mallet (usually included) and basic hand tools like a wrench or socket set. Read through the instruction manual before you start; Thule provides a PDF read on their website if you have already lost the paper copy.

Check the weight limit of your roof rack before you load the box. The Motion XT XXL itself weighs about 75 pounds empty. Most roof racks have a weight capacity listed in the manual — typically 100 to 150 pounds total. This means you cannot fill the box completely on every vehicle; you need to account for the box's own weight plus the cargo inside.

How to install the Motion XT XXL on your roof

Start by positioning the box on your roof rack before you tighten anything. The box should sit centered on the rack, with equal overhang on both sides. Thule boxes are designed to work with most standard roof rails, but the exact positioning depends on your rack width.

Attach the clamps to the roof rails using the hardware provided. Thule includes a set of clamps that slide into the rails and tighten with a wrench. Tighten each clamp in a crisscross pattern — similar to tightening wheel lugs — so the box sits evenly. Do not over-tighten; you want the clamps snug enough that the box does not shift, but tight enough that you can still move it by hand with moderate force.

Once the clamps are find, open and close the lid several times to make sure it moves freely and latches properly. Check that the rubber gasket around the opening sits flush and has no gaps. If the lid does not close smoothly or the gasket is pinched, loosen the clamps slightly and reposition the box.

After installation, drive at normal highway speeds for 10 to 15 minutes, then pull over and check that all clamps are still tight. The box may shift slightly during the first drive as everything settles. Check again after a few more trips before you consider the installation complete.

Loading and weight distribution inside the box

Place heavier items toward the center and front of the box, closer to where it mounts on your roof rack. This keeps the weight balanced and reduces stress on the clamps. Avoid loading all the weight to one side or toward the rear of the box, which can cause the box to tilt or put uneven pressure on the mounting points.

Pack soft items like clothing and blankets around harder objects to prevent them from shifting during turns or sudden stops. The box has no internal dividers, so items can slide around if you brake hard or take a sharp corner. Use packing cubes or small bags to organize contents and keep them from moving.

Do not exceed the weight capacity of your roof rack. If your rack is rated for 150 pounds total and the box weighs 75 pounds, you have 75 pounds of cargo space left. Overloading puts stress on the roof, the clamps, and your vehicle's suspension, and it voids the warranty on both the box and the rack.

Maintenance and seasonal storage

After each trip, wipe down the exterior of the box with a soft cloth to remove dirt and salt spray, especially if you drove near the ocean or in winter conditions. Check the rubber gasket around the lid for cracks or hardening. If the gasket becomes brittle or no longer seals properly, Thule sells replacement gaskets that you can install yourself by removing the lid and sliding out the old gasket.

Lubricate the hinges and latch mechanism twice a year with a light machine oil or silicone spray. This keeps them moving smoothly and prevents rust. Avoid using heavy grease, which attracts dirt and can gum up the mechanism.

If you remove the box for storage, keep it in a dry location out of direct sunlight. UV exposure can fade the plastic over time and make the gasket brittle. Store the clamps and hardware in a small bag so you do not lose pieces before the next installation. If you leave the box on your roof year-round, inspect the gasket and clamps every few months, especially before winter or after heavy rain.

Fuel economy and driving considerations

A roof box increases wind resistance and adds weight, which reduces fuel economy. Most drivers report a 5 to 15 percent decrease in miles per gallon when a roof box is installed and loaded, depending on highway versus city driving and how full the box is. Highway driving shows a larger impact because aerodynamic drag increases with speed.

The box adds approximately 4 feet to your vehicle's height. Before driving, check the clearance of any low structures you plan to pass under — parking garage entrances, drive-through car washes, tree branches over driveways, and low-hanging power lines. Many people forget about the added height and damage the box or their vehicle by driving under something too low. If you are unsure about a clearance, get out and measure or find an alternate route.

Wind noise increases noticeably at speeds above 50 miles per hour, particularly if the box is not perfectly sealed or if the gasket is worn. This is normal and does not indicate a problem, but it can make highway driving louder. Some drivers find the noise bothersome; others do not notice it after a few trips.

Comparing the Motion XT XXL to other Thule boxes

Thule makes several roof box models in different sizes. The Motion XT XXL is the largest in the Motion line, holding 26 cubic feet. The Motion XT XL holds 18 cubic feet and is lighter and more aerodynamic. The Motion XT is the smallest at 15 cubic feet. If you do not need the full 26 cubic feet, a smaller box will reduce wind noise and fuel economy loss.

Thule also makes the Roof Box line, which includes models like the Touring and Touring L. These are generally less expensive than the Motion line but have a more traditional rectangular shape and may be louder at highway speeds. The Motion line has a more aerodynamic design that reduces noise and drag compared to older box styles.

If you want a permanent roof solution, Thule makes roof baskets and cargo carriers that mount directly to roof rails without a separate box. These are open-top designs that work well for bulky items like camping gear or lumber but do not protect contents from weather or theft the way a closed box does.

Frequently Asked Questions

Can I install the Motion XT XXL on a vehicle without factory roof rails?

No, you need an existing roof rack system. If your vehicle does not have factory rails, you must purchase and install an aftermarket roof rack first. The box itself only provides the clamps to attach to the rack; it does not replace the rack.

Does the box come with a roof rack?

No. The Motion XT XXL is the cargo box only. You must purchase a roof rack separately that matches your vehicle model. Thule and other manufacturers sell racks designed for specific vehicles, so check your car's year, make, and model before ordering.

How do I know if my roof can handle the weight?

Check your vehicle's owner manual for the roof weight capacity. Most vehicles can handle 150 to 200 pounds on the roof, but some smaller cars are rated lower. The Motion XT XXL weighs 75 pounds empty, so subtract that from your roof's capacity to find how much cargo you can safely load.

Can I leave the box on my car year-round?

Yes, but you should inspect the gasket and clamps every few months. Winter salt, UV exposure, and temperature changes can degrade the rubber seal over time. If you do not use the box regularly, removing it when not needed extends its lifespan and improves fuel economy.

What is the difference between the dual-side opening and a standard opening?

The dual-side opening means the lid can open from either the left or right side of your vehicle, depending on where you parked. This is convenient if you are parked close to another car or a wall. Standard boxes open from one side only, which can be inconvenient in tight parking spaces.