Many cars cannot tow 750kg unbraked as that is the absolute legal maximum, many cars can only tow in the region of 450kg to 650kg unbraked so there are plenty of axels out there that have brakes even though they are rated at 750kg or less.
If you think logically a car will weigh much more than the unbaked trailer it can tow ware as an ATV will weigh much less than the trailer they are asked to tow even with the rider on it, the unbaked trailer capacity of ATV is very small if you look at the machine specs.
Lets say your ATV weighs 250kg (without rider) and is 4x4 with brakes on all wheels, on tarmac or other hard dry ground it will be good for ~75% of its weight to convert into any form of traction, thus with its brakes locked you will yield 187.5kg of holding force, on dry grass it will yield ~35% of its weight to convert into traction or 87.5kg of holding force, if it lightly rains on that grass the adhesion will drop much lower down to ~25% or ~62.5kg of holding force.
Now if you bare the above paragraph in mind and its simple concept of converting mass in to adhesion (grip) base on the factor of adhesion % that a surface will yield wile reading the paragraph below you will realise why people get into trouble with trailers and slopes especially when condition change with a little bit of rain.
As most of you know when the vehicle you are driving comes to a hill it slows down, the steeper the hill the more power you need to maintain speed and the greater the affect of slowing down is in the absence of sufficient power, slowing down happens because unlike travailing on the flat ware the effects of gravity are negated a % of gravity based on angle of incline will be working to resist you assent, a vertical incline (90deg) will yield 100% of gravity or in ATV terms relating to this thread and the above example that would be 250kg + 750kg of trailer equalling 1000kg pulling you down and because of the absurd angle (mealy for the point of illustration) non of that mass would be acting on the wheels, on a 45deg slope the effects of gravity are 50% so you have 50% of your total mass trying to pull you down hill or in other words 500kg of force, on a 22.5deg slope you have 25% of your total mass trying to pull you down hill or in other words 250kg of force and logically if you are keeping up with the above you realise that on a 11.25deg slope it is 12.5% of your mass trying to pull you down hill (125kg) and for a 5.625deg slope its 6.25% of your mass (62.5kg), so in short for each 1deg of slope you get 1.111111% of your mass acting agenised you to pull or push you down hill.
So in a situation ware you are using an unbraked trailer a modest slope on e.g. grass it can be a killer especially when conditions have changed during a working day due to a bit of light rain, if you have brakes on your trailer then any weight on the trailer generates braking force in addition to the ATV so if you look 3 paragraphs above (Lets say your ATV weighs 250kg………..) and if you work the % for a 750kg loaded braked trailer in addition the ATV it makes a marked contrast in holding force given in the example the trailer weighs 3 times more than the ATV
Just remember the calculation for holding force vs. ground factors MUST exceed gravity’s pull or you will be at its mercy.
Just in case any one wanders, the drivers of the tractors in the pictures all survived yet you can see even a ROPS’s cab can only do so much and an ATV doesn’t have a ROPS or much else and 750kg of trailer is more than enough to kill you if it runs you over or impacts you agenised a tree all for the want of some brakes!