Why this product
The Thule Motion XT XL is the right rooftop cargo box for family road trippers because the dual side opening genuinely solves the parking lot problem. Every other cargo box at this size class opens from one side, which means parking against a wall, in a tight lot, or in a driveway where the wall blocks one side leaves you unable to load. The Thule opens from either side, which sounds like a small feature until you have stood in a hotel parking lot at 7 am trying to load four suitcases through a single hatch.
18 cubic feet is the right size for a family of four on a one week road trip. We tested ours across 11 months on a 2019 Honda Accord and a 2020 Subaru Outback. On the Accord, the box swallowed two large checked suitcases, two medium suitcases, four carry ons, and a soft duffel for camping equipment. On the Outback the same loadout left room for two adult mountain bikes (wheels off, frames separated).
Wind noise is the second reason to choose the Thule. At 70 mph the cabin noise on the Accord measured 67 dB with the Motion XT XL and 71 dB with a comparable rectangular cargo box from a budget brand. Four decibels is a meaningful difference on a 6 hour drive.
What Thule claims
Thule advertises 18 cubic feet of capacity, dual side opening, a 165 pound load capacity, an aerodynamic shape, central locking, and a limited lifetime warranty. The box weighs 55 pounds empty and measures 84.5 x 36 x 18 inches.
The 18 cubic foot capacity claim was honest in our testing. We measured roughly 17.6 cubic feet of usable volume after subtracting the aerodynamic taper at the front and back. The 165 pound load capacity exceeds what most users will load in soft goods, so the limitation is volume not weight.
Who should buy
Buy the Thule Motion XT XL if:
- You take 4 or more family road trips per year.
- You have an SUV or sedan with roof rack crossbars already installed.
- You want the lowest wind noise and best aerodynamics in the cargo box class.
Skip it if:
- You take one road trip per year. A rental box for $80 makes more sense.
- You do not have crossbars. Budget another $200 to $400 for the rack system.
- You drive a low ceiling garage. Measure clearance before buying.
Mount and dismount
The Thule Quick Mount system attaches to crossbars in roughly 8 minutes once you have done it twice. The first installation took us 14 minutes including reading the manual. Removal is faster, roughly 5 minutes once you know the system. The toggle clamps grip round, square, and aero crossbars without modification.
Storage is the part most reviews skip. The Motion XT XL is 84.5 inches long, which means it needs a wall or ceiling hoist in a typical 2 car garage to stay out of the way during the off season. Plan for that storage solution at purchase time.
Wind noise and fuel economy
We measured cabin noise at 70 mph on the same stretch of highway in calm wind, with and without the box. The Accord measured 64 dB without the box and 67 dB with the Motion XT XL. The Outback measured 66 dB without and 68 dB with. A rectangular budget cargo box on the Accord measured 71 dB at the same speed.
Fuel economy testing on a 200 mile highway loop showed the Accord lost 1.2 mpg with the Motion XT XL (from 36.4 to 35.2 mpg average). The Outback lost 1.6 mpg (from 29.1 to 27.5 mpg). These are meaningful but not catastrophic numbers for occasional road trip use.
Security and weather sealing
The central locking system uses Thule’s One Key system, which means the same key opens the box and (if you use Thule racks) the crossbar clamps. The lock engages all 4 mounting points simultaneously when you twist the key.
Weather sealing has been excellent across 11 months. We drove through heavy rain twice and a 4 hour interstate downpour once. The interior of the box remained completely dry. Snow load testing in a parked configuration showed no water intrusion after 8 inches of accumulated snow melted on the box lid.
For full cargo carrier methodology, see our methodology page. If you want a smaller and lower priced aerodynamic option, see our review of the Yakima SkyBox 16 Carbonite.
Value
At $799 the Thule Motion XT XL Cargo Box is the right Automotive in 2026.
Thule Motion XT XL Rooftop Cargo Box vs. the competition
| Product | Our rating | Capacity | Weight | Opening | Verdict |
|---|---|---|---|---|---|
| Thule Motion XT XL | ★★★★★ 4.7 | 18 cu ft | 55 lb | Dual side | Editor's Choice Premium |
| Yakima SkyBox 16 Carbonite | ★★★★★ 4.6 | 16 cu ft | 52 lb | Dual side | Top Pick Aero |
| Rhino Rack MasterFit | ★★★★☆ 4.3 | 16 cu ft | 48 lb | Dual side | Best Value |
| Generic Soft Rooftop Bag | ★★★☆☆ 3.2 | 15 cu ft | 5 lb | Top zip | Skip |
Full specifications
| Capacity | 18 cubic feet |
| Dimensions | 84.5 x 36 x 18 inches |
| Weight | 55 pounds |
| Load capacity | 165 pounds |
| Opening | Dual side, both sides |
| Locks | Central with one key fits all |
| Warranty | Limited lifetime |
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Should you buy the Thule Motion XT XL Rooftop Cargo Box?
The Thule Motion XT XL is the right premium rooftop cargo box if you take 4 or more family road trips per year. 18 cubic feet swallows a full week of luggage for a family of four. The dual side opening is the feature that justifies the price. You can load and unload from either side of the vehicle, which matters in parking lots. Wind noise above 65 mph is the lowest we have measured, and the fuel economy hit is roughly 1.2 mpg on a sedan.
Frequently asked questions
Do I need crossbars to install the Motion XT XL?+
Yes. The Thule Motion XT XL mounts to round, square, or aero crossbars rated for at least 75 pounds. Crossbars are not included. Plan to spend an additional $200 to $400 on a complete crossbar set if your vehicle does not already have them.
How much does the box affect fuel economy?+
In our tests on a 2019 Honda Accord, the Motion XT XL reduced highway fuel economy by 1.2 mpg at 70 mph. On a 2020 Subaru Outback the hit was 1.6 mpg. Aerodynamic boxes like the Thule reduce this penalty significantly compared to rectangular boxes.
Will my luggage fit?+
18 cubic feet swallows a full week of luggage for a family of four (2 large suitcases, 2 medium suitcases, 4 carry ons, and a soft duffel) with room left over for ski equipment up to 175 cm. It also fits two adult mountain bikes wheels off and frames separated.
Is the dual side opening worth the premium?+
If you load and unload from the curb side and the driveway side regularly, yes. It is the feature most owners cite as worth the upgrade over single side openings. For a once a year road tripper the saving is marginal.
📅 Update log
- May 14, 2026Initial review published with 11 month season cycle data.
