GarageCalc Why the 8 to 12 percent band exists
A caravan is stable when a modest share of its weight bears down on the car, keeping the coupling loaded and the van's nose planted. Around 10 percent of the loaded van does that job; 8 to 12 percent is the practical range Australian vans are designed around.
- Too little (under 8%): the van's mass sits behind its axles, it starts to pendulum at speed, and a gust or a passing truck can turn that into sway. This is the classic cause of caravan rollovers.
- Too much (over 12%): the car's rear squats, steering goes light, the rear axle and tyres run near their limits, and you burn car payload you needed for people and gear.
Three limits, and the lowest one wins
Ball weight has to sit under every one of these at once:
- The towbar rating, stamped on the towbar plate (commonly 250 or 350 kg).
- The vehicle manufacturer's limit, in the owner's manual, sometimes lower than the towbar.
- The car's payload and rear axle capacity, because ball weight is carried by the car and counts against GVM. Some makers publish loading tables that cut the permitted ball weight as payload rises; Nissan's Navara reaches 0 kg permitted ball weight at full GVM.
Our vehicle pages list the ball limit alongside GVM and GCM by year and variant.
How to get it right
- Load the van exactly as you tow it: water, gas, fridge, gear, bikes.
- Measure with a ball weight scale. The plate's unladen figure means nothing once packed.
- If it is under 8 percent, move heavy items forward of the van's axle; if over 12, move them rearward or into the car (mind the car's GVM).
- Re-measure after any big change in how you pack, especially water.
The caravan weight calculator shows your ball weight percentage as you change the load, and the caravan towing calculator checks it against your car's limit alongside ATM, GVM and GCM.
Frequently asked questions
What is the 10 percent rule for tow ball weight?
A widely used Australian guideline that the static download on the tow ball should be about 10 percent of the loaded caravan mass, with 8 to 12 percent as the practical band. Below that, the van can sway; above it, you overload the car's rear axle and use up its payload. It is a guideline, not law; the legal limits are the towbar and vehicle ball ratings.
How do I measure ball weight?
With the van fully loaded as you will tow it, use a purpose-made ball weight scale under the coupling, or a bathroom-scale and lever method for a rough check. The compliance plate lists an unladen ball weight, which is nearly useless once the van is packed; measure the real thing.
Does ball weight count against the car's payload?
Yes, fully. Every kilogram on the ball is carried by the car, so it counts against GVM and rear axle capacity. A 350 kg ball weight on a car with 700 kg of payload leaves 350 kg for everything and everyone else.
My towbar says 350 kg but my car's manual says less. Which wins?
The lower number, always. The towbar, the vehicle manufacturer and sometimes a loading table in the owner's manual can each set a limit, and you must stay under all of them. Nissan's Navara, for example, reduces the permitted ball weight as vehicle payload rises, all the way to zero at full GVM.