Guide

Dynamic versus static roof load

The number printed on the rack box is almost never the number that decides which tent you can buy. There are three separate figures, they belong to three different companies, and the one that governs is the smallest. Here is how to find it, with the arithmetic done on real vehicles.

Unlike “four-season”, this one does have a standard

We wrote in the four-season guide that no standard anywhere defines what a tent must do before it can be called four-season. Roof racks are the opposite case. There is a real international standard, and most of the market never mentions it: ISO 11154:2023, Road vehicles — Roof load carriers, which replaced the 2006 publicly available specification and was amended again in 2025.

It covers racks for passenger cars and light commercial vehicles up to 3.5 t, and racks fitted to trailers. Magnetic and suction-mounted racks are explicitly excluded from it. The testing is not a formality:

  • Five samples are tested, in the mounting position least favourable to the user — a height-adjustable rack is tested at its highest setting.
  • A lane-change test, run on the severe obstacle-avoidance course of ISO 3888-2. In plain terms, the rack and its load are put through an emergency swerve.
  • A brake test. Both of these were added in the 2023 edition; the 2006 specification had neither.
  • Vibration resistance, with an informative annex specifying a Belgian-block cobblestone test track.
  • Crash simulation stress, corrosion and weather resistance, and lock and hinge testing on roof boxes.
  • A temperature envelope of −20 °C to +60 °C, across which the rack and its accessories must still meet the operational-safety, static-load and crash requirements.

Worth being clear about what the standard is not. ISO 11154 is a voluntary standard, not Canadian law. Unlike tents — which are regulated here under the Tents Regulations — a roof rack sold in Canada is not required to have been tested to it. So “tested to ISO 11154” is a real claim worth asking for, and its absence is not an offence.

Three numbers, three different owners

This is the part that causes the confusion, and the standard itself is clearer about it than any retailer. ISO 11154 defines separate symbols for three separate quantities, and gives over an entire annex to determining the payload from them:

SymbolWhat it isWho publishes it
mDPermissible roof load, in kgYour vehicle manufacturer
mNPermissible load-bearing capacity of the rack, in kgYour rack manufacturer
mEDead weight of the rack itself, in kgYour rack manufacturer

What you may actually put on the roof is not any of those three. It is what is left when you take the lower of the first two and subtract the third:

Tent allowance = the lower of (vehicle limit, rack limit) − the weight of the rack.

Thule states the same thing in the safety instructions packed with its roof racks and accessories: the rack’s own maximum is subordinate to the figure the car manufacturer gives, the lower of the two always applies, and the roof load is the carrier weight plus any fitted accessories plus the load itself.

Two consequences follow immediately, and between them they account for most of the disappointment in this market.

1. A big number on the rack box buys you nothing

An aftermarket platform rack advertising 250, 400 or 700 lb does not raise your vehicle’s limit by a gram. If the manual says 45 kg, the answer is 45 kg with a 700 lb rack bolted to it. While checking this we found two listings for the same rack quoting different ratings, which is a fair summary of how much weight to put on that number.

2. The weakest link is often a part you did not think about

A rack is not one rating. The bars, the feet, the fit kit and the tray can each carry their own figure, and the lowest one governs the assembly. One retailer documents a Thule setup whose load bars are rated 165 lb while the foot pack and fit kit beneath them are rated 130 lb — so the bars were never the constraint.

The sharpest version of this we found is a Toyota. The 2019–2026 RAV4 manual gives 80 kg for the roof. Toyota’s own genuine crossbar set, part PT278‑42151, is rated 45 kg. Fit the manufacturer’s own accessory to the manufacturer’s own car and your limit falls by 35 kg. This also explains a conflict we had previously recorded on the fitment page: the 100 lb figure circulating for the RAV4 is the crossbar rating, not the vehicle’s.

The arithmetic on real vehicles

Below is every vehicle on our fitment page for which we have a published driving figure, with the tent allowance worked out. We have assumed a light 7 kg aluminium aero bar pair, which is at the better end of what is available; a steel bar set or a platform rack can weigh three times that, and it comes straight off the allowance.

VehiclePublished driving limitBars counted in?Left for a tent
Jeep Wrangler JL 2018–2645.4 kgYes — the manual says so38.4 kg
Jeep Gladiator 2020–2645.4 kgYes38.4 kg
Ford Bronco hardtop 2021–2649.9 kgNot stated42.9 kg
Toyota 4Runner 2010–2454.4 kgNot stated47.4 kg
Subaru Crosstrek 2016–2668.0 kgYes61.0 kg
Subaru Outback 2020–2468.0 kgNot stated61.0 kg
Subaru Outback 2014–1974.8 kgThe factory rack is the limit — the roof is rated 80 kg, the rack 74.874.8 kg
Toyota RAV4 2019–2680 kg — but 45 kg on Toyota’s own barsThe accessory governs45 kg
Subaru Outback Wilderness 2022–2699.8 kgYes92.8 kg

Five of those nine leave under 50 kg for the tent. The two Jeeps leave 38 kg, and most hard-shell roof tents on the Canadian market weigh 55 kg or more before you add a single bar. That gap is not a detail of this business, it is the whole of it, and it is why our sourcing brief refuses to quote a two-person hard shell over 45 kg net.

Where the manufacturer publishes nothing. Ford does not state a roof figure for the F‑150, and owners checking the Tacoma manual report the same. In that case the rack’s own driving rating is the only limit you have, which makes knowing it far more important rather than less. Third-party guides quoting 150–250 lb “by trim” for these trucks cite nothing, and we do not repeat them.

Static load: the part almost everyone gets half right

The received wisdom is that the static limit — parked — is three to five times the driving limit, so the people asleep in the tent are never the constraint. That is mostly true, and the half that is missing matters.

First, ISO’s “static” is not your “static”

ISO 11154 does have a clause on static load-bearing capacity. It is a structural strength test: forces applied along the direction of travel, against it, at 20° to it, vertically and laterally, with the resulting displacement measured. The 2023 edition shortened the force application from ten minutes to one. It is not a published allowance for a parked vehicle with people in it, and the standard defines no symbol for one. An ISO-tested rack has not thereby been rated for occupancy.

Second, the uplift belongs to the roof, not to the rack

Where a vehicle manufacturer publishes both figures, the multiple is real and generous:

VehicleDrivingParkedMultiple
Ford Bronco hardtop49.9 kg204.1 kg4.1×
Subaru Outback Wilderness99.8 kg317.5 kg3.2×

Subaru is the only maker in our dataset that addresses roof tents directly, and it deserves the credit: the 2022 Outback loading section gives a total roof-rail figure that expressly includes a roof tent and its occupants and contents, then requires that occupants and cargo come off the tent before the vehicle moves. That is the dynamic-versus-static distinction written by a manufacturer rather than by a forum.

Where a rack maker publishes both, the multiple is far smaller — and sometimes there is none at all:

  • Rhino-Rack’s dealer-facing explanation puts the static figure at roughly twice the driving rating, and one Backbone listing is 370 lb driving against 660 lb parked — 1.8×, not four.
  • Many products have no static rating at all. A 220 lb heavy-duty rack was confirmed by a retailer’s technical desk as a driving figure with no parked figure published.
  • Front Runner declined to give a retailer either rating for one platform rack, pointing to the vehicle’s limit instead. Its trays are widely listed at 660 lb static.
  • Thule’s general safety instruction for its roof racks and accessories is blunter still: “Maximum load applies to driving as well as parked vehicle.”

So the honest rule is the earlier rule applied to a different column: your parked limit is the lower of the vehicle’s static figure and the rack’s static figure — and if your rack does not publish one, you do not have one to rely on. Products actually designed to carry a tent do state occupancy limits. Ask for it in writing, for your exact part number, and do not compute it from the driving figure with a multiplier you read somewhere.

The case where the occupants really are the constraint

We went looking for a counter-example to our own advice and found one on a common vehicle.

Statistics Canada’s Canadian Health Measures Survey measured — not self-reported — mean adult weights of 86.0 kg for men and 73.5 kg for women aged 40 to 59. Take a couple in that band, a 45 kg hard-shell tent and a 7 kg bar set, on a Ford Bronco:

On the roof, parkedkg
Tent45.0
Bars7.0
Two adults, 86.0 + 73.5159.5
Total211.5
Ford’s published static limit204.1
Over by7.4

An average Canadian couple in their forties, in a tent at our own sourcing ceiling, is over Ford’s published parked limit before anyone carries a sleeping bag up the ladder. Two men at that mean figure would be roughly 20 kg over. Owners also report that the Bronco’s hardtop is a structural member and visibly bows under load, which is at least consistent with a limit lower than the segment’s.

And here is the part that changed our mind. Swap that 45 kg hard shell for a 32 kg soft shell and the same couple lands at 198.5 kg — inside the limit, with 5.6 kg spare. Tent weight is not only a driving problem. On a tightly rated roof it decides whether you are within the limit while asleep. We had been making the weight argument on the dynamic figure alone. It holds on the static figure too, and we had not noticed.

Where the standard stops at the Canadian border

Three limits stated clearly in the documents and almost never repeated in the showroom:

  • −20 °C is the floor of the standard’s temperature envelope. A rack tested to ISO 11154 has been validated down to −20 °C, not below. Compare that with our own province data: a Yellowknife or Whitehorse winter sits well under it for months, and so does a cold snap on the prairies. Leave a loaded rack on the vehicle through a Canadian winter and you are outside the envelope its plastics were demonstrated in. This is an argument for taking the tent off in November, which you wanted to do anyway.
  • 130 km/h is Thule’s absolute ceiling with a load, and it instructs 10 km/h over speed bumps. Highway limits in most provinces are 100–110 km/h, so the speed limit is doing that work for you — but the speed-bump figure is the one people break daily.
  • Off-road ratings are lower, and usually not published. Rhino-Rack applies reductions off the sealed-road figure. If your plan is a forestry road in BC or a gravel highway in the territories, the number on the box is not the number you are operating under — and the vibration testing in the standard is run on cobblestones rather than washboard.

One more, because it is free: ISO 11154 runs its tests at a bar spacing of 700 mm, and Thule asks for a minimum of 700 mm between bars wherever its instructions do not say otherwise. If your vehicle’s fixed mounting points force the bars closer together than that, you are outside both the test geometry and the instruction — and a roof tent, which spans both bars and loads them near their ends, is the least forgiving thing you can put up there.

What to do, in order

  1. Find your vehicle’s own figure, in your own manual. Not a forum, not a rack seller. Our fitment page gives what we have been able to cite and says plainly where we could not. Check whether the wording includes the bars — Jeep, Subaru and Toyota all phrase this differently.
  2. Find your rack’s driving rating, and the ratings of its feet and fit kit. The lowest of them is your rack figure.
  3. Subtract the rack’s own weight from whichever of the two is smaller. That result, and nothing else, is your tent budget.
  4. Then ask for the parked figure — from the vehicle maker and the rack maker — and add up tent plus bars plus everyone who will be up there. If either party does not publish one, treat the driving figure as the limit until someone puts a number in writing.
  5. Only now look at tents. Soft shells exist precisely for the roofs in the first half of that table; hard shells buy you setup time and cost you the thing you have least of. Bar weight is worth real tent weight, which is why we ask suppliers for a pair under 8 kg.

A correction to our own pages

Our fitment page and four-season guide both said that static load is three to five times the driving limit, so the occupants are not the constraint. On the evidence above, that is right about the vehicle’s roof and wrong about the chain: the rack may grant no uplift at all, and on a Bronco with a 45 kg tent the occupants genuinely are the constraint. We have corrected both pages to say that the lower of the two figures governs. We would rather publish the correction than quietly edit it.

Sources — ISO 11154:2023 Road vehicles — Roof load carriers (scope, symbols, clauses 6.3, 6.5, 6.11, 6.12 and annexes B and C; first edition 2023‑03, amended 2025), and the Thule safety instruction packed with its roof racks and accessories (document 501‑8420‑03, sections A.4, B.1, B.3, C.1 and C.2). Vehicle figures are the ones cited on our fitment page, each with its own source and confidence note. Rack ratings are as reported by Rhino-Rack, Front Runner and their retailers’ technical desks. Body weights are measured means from the Canadian Health Measures Survey, Cycle 2, 2009–2011, Statistics Canada — an archived table, and the most recent measured national figures we could cite rather than self-reported ones.