MTPLM / MAM — the mass the van must never exceed, total or per axle.
01 / THE NUMBER
Where 370 kg comes from.
Every UK campervan carries a legal ceiling: the MTPLM (maximum technically permissible laden mass — also called MAM). For the Nebuchadnezzar, a Swift Trekker X Automatic, that ceiling is 3,500 kg — the limit that keeps it drivable on a standard category B licence and out of goods-vehicle rules.
From that ceiling, subtract what the van weighs before you load it: the MRO (mass in running order). Convention matters here, because MRO isn't an empty van — it typically already includes essential fluids, a 90% fuel tank and a nominal 75 kg driver. On the Trekker X Automatic's published figures that leaves a quoted user payload of 370 kg.
Three hundred and seventy kilograms sounds generous. It is not. It's everything and everyone the van will ever carry beyond that nominal driver — and the automatic gearbox, worth having in every other way, already cost payload against the manual before the first bag went in.
Derived MRO — including fluids, ~90% fuel and a 75 kg nominal driver.
Quoted user payload — crew, dog, water, gas, food, kit, toys, all of it.
02 / THE ARITHMETIC
Watch it disappear.
Illustrative round numbers — your crew and kit will differ, which is exactly why the calculator is editable. The pattern, though, is universal.
The humans
A 75 kg driver is already counted — anything above it is payload. An 80 kg driver adds 5 kg; a second adult at 65 kg is all payload; an infant plus child seat, call it 15 kg. Running total: ~85 kg.
The dog and his crate
A medium dog plus a crash-tested crate anchored on the activity deck — illustrate it at 25 kg. Highway Code rule 57 makes the restraint non-negotiable; physics makes it payload. Running total: ~110 kg.
Water is a kilogram a litre
Touring with 20 L fresh (of the 65 L tank) is 20 kg; a gas bottle at ~11 kg gross rides along; waste travels empty if you're disciplined. Running total: ~141 kg.
Kit, food, everything soft
Bedding, clothes for four seasons, the galley box, food and drink, chairs, tools, hoses, cables, buggy, toys, boots. Families are routinely astonished this alone clears 100–150 kg. Running total: ~260–290 kg.
What's actually left
From 370 kg, perhaps 80–110 kg of headroom remains — before the awning, the bikes and rack, the paddleboard, the second gas bottle or the "just in case" box. The big-ticket accessories arrive precisely when the margin has already gone.
Quoted figures hide choices
Published payloads lean on the 90% fuel and 75 kg driver conventions, and factory options fitted to a real van can quietly reduce them further. The calculator surfaces every assumption and lets you edit each one.
03 / WHY IT BITES
Overweight isn't a rounding error.
Running past the MTPLM is an offence for the driver, and enforcement weigh-checks happen. It can also bite through the axle limits — a van can be legal on total mass yet overloaded on the rear axle because the garage, the water and the bikes all live behind the wheels. Total and per-axle both have to clear.
Beyond the law: braking distances stretch, the rear sits down, crosswind manners deteriorate, tyres and suspension work outside their design case, and an insurer confronted with a claim has an obvious question to ask. None of this is scaremongering — it's just what mass does.
And the everyday cost is subtler: an overweight habit means every ferry booking, every weighbridge ticket and every "shall we take it?" decision carries a background anxiety the trip doesn't need. The families who weigh once, properly, tour lighter in both senses.
04 / THE DOCTRINE
The weighbridge ritual.
The same check card appears on all eight expedition files, because it's the one that matters most.
Pack the real trip
Not a guess, not "mostly loaded" — crew, Percy, water at touring level, gas, food, every bag, exactly as you'd roll out of the drive.
Visit a public weighbridge
Get total mass and, where the bridge allows, each axle. Keep the ticket — it's the ground truth every estimate answers to.
Feed the calculator
Compare the ticket with the tool's estimate, adjust the inputs until they agree, and you now own a model of your van you can trust between weighings.
Cut before you carry
If the margin's thin: travel with less fresh water and fill on arrival, empty waste religiously, audit the "just in case" box, and question every accessory that lives aboard full-time.
05 / RUN THE TOOL
Preloaded with the Landship. Editable for yours.
The Payload Core on the Tools deck runs from a shared vehicle profile — the Trekker X Automatic's 3,500 / 3,130 / 370 figures are the factory baseline, and every number is editable for any similar van. Adjust crew, liquids, gas and kit; it shows the live remainder and flags the red zone before the weighbridge does.
It saves locally in your browser, needs no account, and pairs with the Off-grid Core — because the two questions every touring plan must answer are can we carry it? and can we power it?