This is a single-product review of one cargo box: the Yakima SkyBox NX 18, the flat-floor family pick in our best rooftop cargo box guide. If the shortlist already convinced you and what you need is the deep dive on this one box — its roof maths, its honest load cap, and the three boxes that beat it for some buyers — start here. The full shortlist lives in the rooftop cargo boxes archive alongside our accessories hub.
Two honesty notes before the verdict. This review covers exactly one SkyBox variant: the NX 18, part number 8007370, the variant our pillar research verified against Yakima’s own specification. Yakima has discontinued other SkyBox variants, and older boxes still circulate in listings — none is reviewed, specified or linked here, so check the part number, not just the SkyBox name, before you buy. Yakima also publishes no internal dimensions for this box — that gap is printed wherever packing is discussed, never filled in.
How we researched this guide
We reviewed 1 cargo box in depth — the Yakima SkyBox NX 18, model 8007370 — taking every specification from the maker and retailer spec tables gathered for our pillar guide, where its Amazon listing was verified against part number 8007370 and the matching UPC. We set it against 3 alternatives from the same verified pool: the Thule Force XT XL, the Thule Motion XT XXL and the INNO Shadow 16, so every comparison figure traces to a spec sheet actually read for this site.
Owner evidence is paraphrased and linked, never quoted at length: a long-term magazine review of this exact box, an expert roundup that handled it alongside its rivals, and the roof-box forum threads our pillar research collected (bar flex, rail vibration, economy and crosswind reports). We do not buy or test cargo boxes. Where Yakima publishes no figure — internal dimensions, height off crossbar — this review prints Not published. Roof limits come from vehicle makers, not the box maker.
The 30-second answer
Buy the Yakima SkyBox NX 18 if soft luggage is your real load: 18 cu ft over a flat floor once the torque knob is removed, dual-side opening, SKS locks, a published 24–40 in crossbar spread and Yakima’s limited lifetime warranty, made in the USA. Read its load figure honestly, though: Yakima caps the whole roof system at 165 lb unless your vehicle says otherwise, and at 53 lb the box itself is heavy. Skis past 195 cm? The Thule Motion XT XXL. The same Thule mounting with a lighter lift? The Thule Force XT XL. Garage height first? The INNO Shadow 16.
Reviewed Here: Best Flat Floor
Yakima SkyBox NX 18
The box under review: 18 cu ft over a flat, snag-free floor, dual-side opening, SKS one-key locks and a published fit window — at 53 lb, a heavy lift. Best if duffels and family soft luggage decide the purchase.
Alternative: The Default Thule
Thule Force XT XL
Best if you want the same 18 cu ft with an easier lift: PowerClick mounting that clicks at the correct torque, a published 21.9–35.9 in spread, and 6 lb less to carry than the SkyBox, at 47 lb.
Alternative: Longest and Largest
Thule Motion XT XXL
Best if long skis rule: 22 cu ft and a floor rated for skis to 215 cm, with SlideLock security — but at 55 lb and 91.5 in long, and with no crossbar spread published, it asks the most of your roof.
Alternative: Best Low-Profile
INNO Shadow 16
Best if garage height rules: the lowest shell here at 13.37 in tall, 42 lb, dual-side opening and skis to 182 cm — but US tables list 13 cu ft despite the 16 in its name.
Quick compare — the SkyBox NX 18 against the three alternatives on maker figures. Read the load column carefully: Yakima’s figure is a cap on the whole roof system, while the Thule and INNO figures are box ratings — the distinction decides how much gear you can honestly carry.
| Box | Capacity | Max ski length | Crossbar spread | Warranty | Check Price |
|---|---|---|---|---|---|
| Yakima SkyBox NX 18 | 18 cu ft / 500 L | 195 cm | 24–40 in | Limited lifetime | |
| Thule Force XT XL | 18 cu ft / 500 L | 195 cm | 21.9–35.9 in | Limited lifetime | |
| Thule Motion XT XXL | 22 cu ft | 215 cm | Not published | Limited lifetime | |
| INNO Shadow 16 | 13 cu ft (see review) | 182 cm | 23.5–39.25 in | Limited lifetime |
If the SkyBox is the wrong shape for your roof, the honest next step is the full comparison in our pillar cargo box guide or the head-to-head in Thule Motion vs Yakima SkyBox. The weakest-link maths is the same one our 4Runner winch guide and F-150 winch guide use: the lowest rating in the system is the rating.
How to choose: judging the Yakima SkyBox NX 18
A single-product review still needs the buying criteria, because the SkyBox only makes sense against them. These are the six checks we applied to it — and the same checks to run on any box in our pillar guide before you spend.
The flat floor: why it decides packing
Most boxes lose usable space to a shaped well around the mounting hardware. Yakima’s answer is a torque-limiting knob that comes out once the box is fitted, leaving a flat floor with nothing for straps to snag on. For soft luggage — the load this box is built around — that flat 18 cu ft packs closer to its paper figure than a shaped floor of the same volume. Judge every rival by whether its floor does the same.
Capacity: 18 cu ft, honestly read
At 18 cu ft (500 L) the SkyBox matches the Force XT XL and trails only the 22 cu ft Motion. Yakima frames it as gear for up to four campers, which is the right mental picture: four people’s soft bags, not four hard cases. Yakima does not publish internal dimensions for this box in the sources checked, so you cannot verify a specific suitcase against a paper figure — the 84 in shell length and the flat floor are the packing facts you actually get.
Weight and the system cap
This check catches SkyBox buyers out. The box weighs 53 lb, and Yakima’s instruction cap is 165 lb for the entire roof system — box, crossbars and contents together — unless your vehicle maker states otherwise. On that default, bars and gear share about 112 lb. A rival’s 165 lb box rating sounds identical and is not: it rates the box, not your roof. Do the subtraction in the roof table below first.
Mounting and the published spread
Fit paperwork is where the SkyBox quietly beats the biggest Thule: Yakima publishes a 24–40 in crossbar spread window, the joint widest here, and the universal clamps suit aero, square, round and most factory bars. Measure your spread, confirm it falls inside that window, and use Yakima’s fit checker before ordering, as the long-term reviewers below did. The Motion XT XXL, by contrast, publishes no spread at all in the sources checked — a verification job this box spares you.
Opening, locks and the SKS key system
The lid opens from both sides, which matters on an 84 in box: you load the far end from whichever side is parked away from traffic, and shorter users are not stretching over a tall sill from one side only. The full-metal handle carries SKS locks that secure the contents and lock the box to the vehicle, and one SKS key can run other Yakima carriers too. The Thule pair answer with One Key — your existing ecosystem is a legitimate tie-breaker.
Garage height, hatch swing and storage
The shell is 16.5 in tall on your crossbars, and Yakima publishes no height-off-crossbar figure for it, so add bar height to the shell and measure your own stack; garage regret is the most repeated owner theme our pillar research collected. The 84 in length is shaped for hatch clearance, but check the full hatch swing anyway. Off the car, the box still needs a wall, hoist or garage corner planned in advance.
Roof load limits: what the SkyBox NX 18 leaves you
Yakima frames this box’s limit as a system cap, so the table below is the review in one place: the sourced vehicle figures from our pillar research, with the gear allowance shown as simple subtraction — vehicle figure minus 53 lb of box, before bar weight — so treat every allowance as a best case.
| Vehicle / roof basis | Published figure | After the 53 lb SkyBox | Honest note |
|---|---|---|---|
| Subaru Forester Wilderness (2022+) | 220 lb dynamic | 167 lb for bars + gear | The roomiest sourced case; the only row where the system cap stops being the argument |
| Typical SUV / crossover (Yakima system default) | 165 lb total system | 112 lb for bars + gear | Yakima’s own default: box, bars and contents counted together unless the vehicle states otherwise |
| Honda CR-V (4th gen, 2012-2014) | 165 lb incl. rack + luggage | 112 lb for bars + gear | Owner’s-manual figure: rack and luggage counted together, exactly as here |
| Toyota 4Runner TRD Pro (factory rack) | 110 lb roof + rack combined | 57 lb for bars + gear | The tightest sourced case; the 42 lb INNO or 47 lb Force leaves more, and even then the budget is thin |
Sources for the figures above: Subaru — Forester Wilderness roof figures and 4Runners.com — Toyota roof load reply. The same payload-first thinking governs the truck guides in our truck winch roundup and Tacoma winch guide, and the SUV-specific fit questions are worked through in our cargo boxes for SUVs guide.
Yakima SkyBox NX 18 by budget: who should step across, and to what
No prices appear in this review — listings change, and a tier table built on a stale figure misleads. The tiers below are ownership tiers instead: what each step away from the SkyBox gives up, and what it keeps.
| Tier | What you get | Example pick |
|---|---|---|
| Step across: the easier Thule lift | The same 18 cu ft with PowerClick torque-click mounting and a published spread — you give up the flat floor and the SKS system, and gain a 6 lb lighter lift at 47 lb | Thule Force XT XL |
| Step up: the long-ski buy | 22 cu ft and skis to 215 cm — you give up a published spread, accept 55 lb and a 91.5 in shell, and gain the only floor here that takes 200 cm-plus skis | Thule Motion XT XXL |
| Step down furthest: the garage fit | The lowest, lightest shell here at 42 lb — you give up 5 cu ft against the SkyBox and cap skis at 182 cm, and you accept the name-versus-spec conflict printed in its brief below | INNO Shadow 16 |
| The reviewed box: the flat-floor family buy | 18 cu ft that packs like it, dual-side SKS security and the joint widest published spread — you accept 53 lb and a system cap that must be read as a system cap | Yakima SkyBox NX 18 |
Flat-floor box, torque-click box or low box: the three shapes in this review
| Type | Pros | Cons | Best for |
|---|---|---|---|
| Flat-floor box (the SkyBox NX 18) | Soft luggage packs to the corners; nothing snags straps; published spread and a system-honest load cap | Heavy at 53 lb; internal dimensions not published; lid noted as harder to close one-handed | Families packing duffels; Yakima SKS households |
| Torque-click box (Force XT XL, Motion XT XXL) | Clamps click at the correct torque; glossy shells; the Motion adds the longest ski rating here | Shaped floors pack less honestly; the Motion publishes no spread and is the heaviest lift | Buyers who fit and remove often; long-ski households (Motion) |
| Low-profile box (INNO Shadow 16) | Lowest garage stack; lightest lift here; still takes skis to 182 cm | 13 cu ft on current US tables despite the name; 110 lb load rating is the lowest here | Garage-limited owners; shorter skis; smaller vehicles |
A soft roof bag remains the honest fourth option for twice-a-year use: it folds away, but it is not lockable or a hard shell. Our pillar guide weighs that trade, and our roof rack system guide covers the bars these boxes depend on.
Detailed review: the Yakima SkyBox NX 18
One full product block follows, in the order our reviews always use: why it earns the pick, the full spec list, fits, pros and watch-outs, owner reports, who should not buy it, and what to pair it with. The three alternatives then get shorter, buttoned briefs — their full reviews live in the pillar guide and, for the Motion, in our Thule Motion box review.
Reviewed: Yakima SkyBox NX 18
Reviewed Here — best flat floor in our pool
Why the Yakima SkyBox NX 18 is our pick
The SkyBox NX 18 earns this pick on one honest advantage: it packs like its paper volume. The removable torque knob leaves a flat floor, the nano-texture shell shrugs off scuffs, and Yakima publishes the two figures buyers most need — a 24–40 in fit window and a system load cap stated as a system cap. If your load is duffels for four and your roof figure survives the maths below, this is the family box to buy.
Yakima SkyBox NX 18 key specs
- Model / part number: 8007370
- Capacity: 18 cu ft / 500 L
- External dimensions: 84 x 36 x 16.5 in
- Internal dimensions: Not published by Yakima in sources checked
- Load guidance: 165 lb cap on the total roof system (box + bars + contents) unless the vehicle states otherwise
- Box weight: 53 lb in US listings; 52 lb in Yakima instructions (US figure used)
- Mounting: Universal clamps with removable torque-limiting knob; flat floor once removed; integrated tie-down points
- Crossbar spread: 24–40 in
- Height off crossbar: Not published in sources checked
- Opening / locking: Dual-sided; SKS locks included, full-metal handle locks box to vehicle
- Ski / board capacity: Skis and snowboards to 195 cm; gear for up to 4 campers
- Warranty / origin: Limited lifetime; made in USA
Yakima SkyBox NX 18: fits and best for
Family SUVs and wagons first: vehicles with the roof length for an 84 in shell, a crossbar spread inside 24–40 in, and a roof figure that still leaves a working gear allowance after 53 lb of box. Best for households packing soft luggage for up to four campers and for existing Yakima owners who gain the SKS one-key benefit. On short-roof cars, hatch contact and front overhang need measuring first — the same measure-first habit our mounting guide teaches for bumper gear.
Yakima SkyBox NX 18 pros and watch-outs
Pros
Flat floor once the torque knob is removed — soft luggage packs to the corners
Published 24–40 in crossbar spread, the joint widest fit window here
Load cap stated honestly as a whole-system figure, not a box-only headline
SKS locks secure contents and box to the vehicle; one key runs other Yakima gear
Dual-sided opening helps shorter users load an 84 in box
Watch-outs
53 lb — a heavy lift for one person; plan on two
Internal dimensions not published — hard cases cannot be verified on paper
Lid noted by expert reviewers as harder to close one-handed
On a 110 lb roof figure the box and bars leave only a thin gear allowance
Yakima SkyBox NX 18: what owners report
A long-term magazine review of this exact box found the dual-side opening genuinely useful for shorter users, who can load from whichever side gives the shorter reach, and valued the SKS system because one key can run several Yakima products at once. The reviewers also used Yakima’s fit checker before purchase — the same published-spread check this review recommends. Source: POWDER — SkyBox NX 18 long-term review.
An expert roundup that handled the SkyBox NX against its rivals praised the snag-free flat floor and the dual-side access, while noting the lid is harder to close one-handed and the box feels bulkier than sleeker rivals. That pairing — best packing, less elegant closing — matches the watch-outs in this review. Source: OutdoorGearLab — cargo box roundup.
Owners running boxes on OEM rails warn that the rails themselves can feel weak under a loaded box and transmit wind vibration into the cabin — the recurring theme on 4Runner forums. On a 53 lb box under a system cap, the rail and bars are part of the rating, not an accessory. Source: 4Runners.com — boxes on OEM horizontal rails.
Two cross-box themes complete the picture: factory crossbars can flex and let a box bounce at speed — stiffer bars cured it for one GM SUV owner, per TahoeYukonForum — box bounce and the stiffer-bar fix — and long-haul owners report roughly a 5–10% fuel-economy drop plus crosswind feel with a box fitted, per TDIClub — economy and crosswind reports.
Yakima SkyBox NX 18: who should not buy
Do not buy it for a vehicle whose roof figure is 110 lb, for a load of hard suitcases you cannot verify against unpublished internal dimensions, or for skis past 195 cm. Skiers beyond that figure belong with the Thule Motion XT XXL; solo owners who fit and remove weekly will feel the 53 lb and should weigh the lighter alternatives below.
Yakima SkyBox NX 18: pair it with
Pair it with soft duffels rather than hard cases: the flat floor rewards luggage that fills corners, and the tie-down points keep the load from shifting against the lid. Pack long items along the floor first, then bags into the nose and tail. Keep the rated recovery kit in the cabin, not the box — the safety section lists the pool-verified kit, and our recovery kit guide explains the ratings. No cargo accessory button is printed here, because no cargo accessory ASIN sits in our verified pool.
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Before the first trip, load the box in the driveway and close the lid from both sides with your real bags inside. The flat floor packs honestly, but a lid forced shut over a proud bag is how seals and locks get strained; more pre-drive checks live in our maintenance checklist.
The alternatives, briefly
Each alternative below is a pillar-pool pick with its own verified listing. Each gets its spec snapshot, the honest reason to choose it over the SkyBox, and its own button.
Thule Force XT XL — Best Overall in the pillar guide
Best Overall in the pillar guide
- Capacity: 18 cu ft / 500 L
- External: 82.75 x 33.75 x 17.25 in
- Weight / load: 47 lb / 165 lb box rating
- Spread: 21.9–35.9 in (published)
- Max ski: 195 cm
- Locking: CentralLock, One Key compatible
Choose the Force if the lift matters more than the floor. You keep 18 cu ft and dual-side opening, gain PowerClick clamps that click at the correct torque and a 6 lb lighter carry, and give up the flat floor and the SKS key system. Its owner evidence is the strongest in the pool: a long-term review covering over a year and close to 20,000 miles, through winter cold and summer heat, via Halfway Anywhere — Force XT XL long-term review.
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Thule Motion XT XXL — Longest and largest in the pillar guide
Longest and largest in the pillar guide
- Capacity: 22 cu ft
- External: 91.5 x 37.5 x 18 in
- Weight / load: 55 lb / 165 lb box rating
- Spread: Not published
- Max ski: 215 cm
- Locking: SlideLock, One Key compatible
Choose the Motion only if the SkyBox cannot do the job: skis past 195 cm, or a load that overflows 18 cu ft. You gain 4 cu ft and the longest ski rating here, and accept the heaviest lift at 55 lb, a 91.5 in shell needing hatch and garage checks, and a crossbar spread Thule does not publish — verify it against part 629906 before ordering. Family owner video coverage centres on its simple mounting; see Motion XT family owner review (YouTube).
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INNO Shadow 16 — Best low-profile in the pillar guide
Best low-profile in the pillar guide
- Capacity: 13 cu ft on current US tables (name says 16)
- External: 78.75 x 31.87 x 13.37 in
- Weight / load: 42 lb / 110 lb
- Spread: 23.5–39.25 in (published)
- Max ski: 182 cm
- Locking: Safety Lock — key removable only when locked
Choose the INNO if garage height or a low roof figure is the deciding number: at 13.37 in tall and 42 lb, it is the lowest and lightest shell here, and its Memory Mount fits aero, square, round and most factory bars. The trades are printed, not hidden: current US tables list 13 cu ft despite the 16 in its name, its 110 lb load rating is the lowest here, and owner coverage is thin — retailer Q&A rather than long-term reviews, per etrailer — INNO manufacturer page and Q&A.
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Spec comparison: SkyBox NX 18 vs the alternatives
| Spec | Yakima SkyBox NX 18 | Thule Force XT XL | Thule Motion XT XXL | INNO Shadow 16 |
|---|---|---|---|---|
| Model / part | 8007370 | 6358B / 635801 | 629906 | BRA1210 / BRA1210BK |
| Capacity | 18 cu ft / 500 L | 18 cu ft / 500 L | 22 cu ft | 13 cu ft (US tables; name says 16) |
| External dimensions | 84 x 36 x 16.5 in | 82.75 x 33.75 x 17.25 in | 91.5 x 37.5 x 18 in | 78.75 x 31.87 x 13.37 in |
| Internal dimensions | Not published | 77.5 x 29.5 x 15.25 in | 84.5 x 33 x 16 in | 72 x 25.62 x 11 in |
| Box weight | 53 lb (52 lb in instructions) | 47 lb | 55 lb | 42 lb |
| Load figure | 165 lb total system cap | 165 lb box rating | 165 lb box rating | 110 lb box rating |
| Crossbar spread | 24–40 in | 21.9–35.9 in | Not published | 23.5–39.25 in |
| Mounting | Universal clamps, removable torque knob | PowerClick, torque click | PowerClick, torque click | Memory Mount, universal |
| Opening | Dual side | Dual side | Dual side | Dual side |
| Locking | SKS locks included | CentralLock, One Key compatible | SlideLock, One Key compatible | Safety Lock, key captive until locked |
| Max ski length | 195 cm | 195 cm | 215 cm | 182 cm |
| Warranty | Limited lifetime | Limited lifetime | Limited lifetime | Limited lifetime |
| Check Price |
No score row is printed: we do not test boxes, so there is no measured basis for a number. The load row needs its note — Yakima’s 165 lb caps the whole roof system, while the Thule and INNO figures rate the box alone; your vehicle figure overrides all four, as the roof table shows.
Fitment & installation: getting the SkyBox NX 18 on and right
Start on paper: measure your crossbar spread, confirm it sits inside the published 24–40 in window, and run the vehicle through Yakima’s fit checker, as the long-term reviewers in the owners section did. Fitting is a clamp job: set the box on the bars, centre it, and work the universal clamps down evenly, alternating sides; once they are set, remove the torque-limiting knob and stow it, and the floor is flat for packing. Three checks remain. Open the hatch through its full swing and confirm clearance; measure the fitted stack — vehicle, bars and the 16.5 in shell — against your garage header, because Yakima publishes no height-off-crossbar figure to borrow; and recheck clamp tightness after the first loaded drive and at fuel stops on day one. The method matches how we fit any roof or bumper load in our truck installation guide and receiver mount guide: fit, drive, recheck.
Safety essentials
Roof box safety — six rules
1. The vehicle roof figure is the ceiling: box, bars and gear together, never the box rating alone.
2. Centre the load between the bars and put the heaviest bags low and between the clamps, never cantilevered at the nose or tail; use the tie-down points.
3. Recheck clamp tightness after the first loaded drive, then at fuel stops; a settled clamp is still your job to catch.
4. Lock the SKS handle and confirm it from both sides before driving; the key check is part of the walk-around, not an afterthought.
5. Know your fitted height and write it on the visor; garages, ferries and car parks are where tall loads get struck.
6. Slow down for crosswinds and truck bow-wake: owners report a real push with a box fitted, and a long shell gives the wind more to hold.
The rated vehicle kit that travels with roof gear on our trips — recovery gear rides in the cabin, each item with its own verified button:
WARN Epic snatch block — the rated pulley for a doubled winch line.
GearAmerica tree saver — the wide, low-stretch trunk protector for anchor points.
AMBULL shackles — rated connection points for the recovery kit.
The guides behind that kit: best snatch block for winching, best tree saver strap, best D-ring shackles for recovery and the full essential winching accessories list.
Troubleshooting
| Symptom | Likely cause | Fix |
|---|---|---|
| Box bounces or vibrates at freeway speed | Factory crossbars flexing under the load (the most reported cause in owner threads) | Confirm clamp tightness first; if the bounce stays, fit stiffer aftermarket bars — the fix that worked for the owners in the reports above |
| Whistle or rising wind noise | A clamp or bar end sitting in the airflow, or the box mounted too far forward | Slide the box back within its mount range, centre it, and check bar end caps; some noise with any box is normal |
| Lid is hard to close one-handed | Load pressing up against the lid, or the known two-hand close this box asks for | Repack flatter between the bars using the tie-down points, and close with two hands, pressing both sides evenly before locking |
| Water inside after rain | Lid closed over a strap, bag corner or debris breaking the seal line | Clear the full seal line, close and lock, then check the contents are not forcing the lid up |
| Hatch touches the box | Box mounted too far back for an 84 in shell on a shorter roof | Slide the box forward within its mount range and re-test the full hatch swing before loading |
| Key will not turn or handle will not lock | Lid not fully seated on one side, so the lock cannot engage | Press both sides down evenly, clear anything fouling the seal line, then lock; never force the SKS handle |
Who should NOT buy the Yakima SkyBox NX 18
Low roof-limit owners. On a 110 lb roof figure, a 53 lb box leaves 57 lb for bars and gear combined — the purchase nearly defeats itself. The lighter alternatives above, or the roof maths in our Wrangler guide’s payload sections, come first.
Hard-case packers. Yakima does not publish internal dimensions for this box, so a specific suitcase or case cannot be verified on paper. If your load is rigid and measured, the Force or the Motion publishes its internals — or start from the full comparison in our pillar guide.
Long-ski households. The SkyBox caps skis and boards at 195 cm. Past that figure there is exactly one honest buy in this pool, the Thule Motion XT XXL, and no packing trick changes a floor length.
Thule One Key households. The SKS benefit only pays if your other carriers are Yakima. If your bike and ski carriers already run on one Thule key, the Force XT XL or the Motion XT XXL keeps you on one key instead.
Solo lifters with no storage plan. At 53 lb and seven feet long, this box wants two people and a wall, hoist or corner off the car. If neither exists, a smaller box you can handle — or the soft-bag route in the pillar guide — serves you better; our under-budget cargo box guide shows the lighter end of the pool.
Final verdict
Reviewed → Yakima SkyBox NX 18 — the flat-floor family buy, with a published spread and an honest system cap. Check its price.
Alternative: the easier lift → Thule Force XT XL — same volume, PowerClick mounting, 6 lb lighter. Check its price.
Alternative: the long-ski buy → Thule Motion XT XXL — 22 cu ft and skis to 215 cm, with an unpublished spread to verify. Check its price.
Alternative: the garage fit → INNO Shadow 16 — lowest and lightest, with the name-versus-spec conflict printed. Check its price.
Buy the SkyBox when soft luggage for up to four is the real load and your roof figure survives the subtraction above. The same roof-weight discipline runs through our portable gear guide and car trailer winch guide.
FAQ
Is the Yakima SkyBox NX 18 worth it over the Thule Force XT XL?
For soft luggage, yes; for everything else, it is close. Both boxes hold 18 cu ft and open from both sides, and both cap skis at 195 cm. The SkyBox packs that volume over a flat floor, publishes the wider spread window (24 to 40 in against 21.9 to 35.9 in) and states its load limit as a whole-system cap. The Force mounts with a torque click, weighs 6 lb less and publishes internal dimensions the SkyBox does not. Duffels decide it for the Yakima; the lift and the paperwork decide it for the Thule.
How much weight can I actually carry in the SkyBox NX 18?
Less than a box-only rating would suggest, because Yakima states the limit differently: 165 lb for the total roof system — the 53 lb box, your crossbars and the contents together — unless your vehicle maker states another figure. On that default, bars and gear share about 112 lb, so realistic gear lands under 100 lb once bars are counted. On a 110 lb vehicle figure, such as the 4Runner TRD Pro factory rack, bars and gear share about 57 lb. The vehicle figure always wins.
What crossbar spread does the SkyBox NX 18 fit?
Yakima publishes a 24 to 40 in crossbar spread window for the NX 18: the Force publishes 21.9 to 35.9 in and the INNO 23.5 to 39.25 in, while the Motion XT XXL publishes no spread in the sources checked. Measure the distance between your crossbars, confirm it falls inside 24 to 40 in, and run your vehicle through Yakima’s fit checker before ordering, as the long-term reviewers cited in this review did.
Will the SkyBox NX 18 fit in my garage?
Measure before assuming. The shell is 16.5 in tall, and Yakima does not publish a height-off-crossbar figure for it in the sources checked, so add your roof height and bar height to the shell and compare the total with your garage header, leaving room for the door mechanism. Garage regret is the most repeated theme in the owner forums our research collected. If the stack does not clear, the INNO Shadow 16 at 13.37 in tall is the lowest alternative here.
Can I open the SkyBox NX 18 from both sides?
Yes. The lid opens from either side, which the long-term reviewers of this box singled out as a real help for shorter users: load the far end of the 84 in floor from whichever side gives the shorter reach, and work from the kerb side in most parking. Pack long items along the floor first, use the integrated tie-down points so the load cannot shift, and keep nothing pressing up against the lid line before you lock.
Does the SkyBox NX 18 lock, and can one key run it?
Yes on both counts. SKS locks are included, and the full-metal handle locks the contents and secures the box itself to the vehicle. Because the cylinders are SKS, one key can be set to run this box alongside other Yakima carriers you own — the benefit the long-term review valued most after the dual-side opening. Thule’s alternatives use the rival One Key system to the same end, so the ecosystem already on your roof is a fair tie-breaker.
How heavy is the SkyBox NX 18 to fit and remove?
The box weighs 53 lb in US listings — Yakima’s own instructions list 52 lb, a 1 lb paperwork variance this review prints rather than hides — and at 84 in long it is an awkward one-person lift even for someone strong: the weight is manageable, the span is not. Plan on two people for fitting and removal, and plan where it lives off the car before it arrives. The Force XT XL at 47 lb and the INNO at 42 lb are meaningfully easier for solo owners.
Which SkyBox should I buy — and are older SkyBox models still sold?
Buy on the part number, not the name. This review covers one variant only: the SkyBox NX 18, part 8007370, the variant verified against Yakima’s specification in our research. Yakima has discontinued other SkyBox variants, and discontinued boxes still appear in marketplace listings wearing the same SkyBox name with different sizes and hardware. If a listing does not state part 8007370, treat it as a different product, verify its figures on Yakima’s own pages, and do not carry this review’s specs across to it.
Will a roof box like the SkyBox NX 18 hurt fuel economy?
Owners consistently report that it does. Long-haul owner reports collected in our pillar research — including reports from owners running a Yakima box — put the drop at roughly 5 to 10 percent with a box fitted, alongside a noticeable feel in crosswinds and in the bow-wake of passing trucks. Treat that as an owner-reported range, not a measured figure for this box: your vehicle, speed and load decide the real number. Removing the box between trips is the only complete fix.
Sources & changelog
Manufacturer and retailer specification sources: SkyBox NX 18 listing (8007370); evo — SkyBox NX 18 specifications; Backcountry North — SkyBox NX 18 specifications; Force XT XL listing (6358B); Hub Cycle — Force XT XL specifications; Backcountry — Motion XT dimensions; CARiD — INNO Shadow 16 specifications; RackWarehouse — INNO Shadow specifications.
Owner and vehicle-limit sources: POWDER — SkyBox NX 18 long-term review; OutdoorGearLab — cargo box roundup; Halfway Anywhere — Force XT XL long-term review; YouTube — Motion XT family owner review; etrailer — INNO Q&A; TahoeYukonForum — box bounce fix; 4Runners.com — boxes on OEM rails; TDIClub — economy and crosswind reports; Subaru — Forester Wilderness roof figures; 4Runners.com — Toyota roof load reply.
Changelog — October 18, 2026: guide first published.
By Leo, Founder, WinchInsider
Leo runs WinchInsider’s research desk: maker spec sheets read line by line, owner reports weighed for and against, and no product recommended without a verified way to buy it. More on about us and how recommendations are funded in our affiliate disclosure.
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