Someone please explain to me

[Marakai]

So, with the downrating of the Alltrack towing capacity from the manufacturer 2200kg@8%/2000kg@12% to the flat 1800kg in Australia, I'd like to ask whether anybody is in the know as to the thought process.

Naturally my first thought is just "because Australia is a nanny state and the guvmint knows better than anybody including the makers of the car", but I'll try to give the benefit of the doubt that there is some other actual thought process involved.

Anybody?

[booba]

Maybe it has something to do with the oem towbar and the fact that we don't get that option here? i'm not familiar with the engineering specifics of tow bars so unsure.

[Umai Naa!!]

There is a science behind it, but mostly ADR-related.

A lot of it has to do with the distance from the ground to the ball, and from the ball to the rear axle line. This is where a lot of non-genuine towbars are not ADR-compliant.

[pologti18t]

How about this for a reason.

There seems to be no specific speed restrictions for towing such things as caravans in Australia (NSW).

In UK the maximum towing speed limit is 60mph (96km/h) on motorways
In Europe (Germany) the normal towing speed limit seems to be 80km/h. To tow at 100km/h you have very specific regs you have to pass. One reg is that the caravan cannot weigh more than 100% of the tow vehicle. If I am not mistaken an Alltrack is getting towards 1800kg

[Umai Naa!!]

No license requirements either, which is a worry.

Nothing stopping Ma and Pa Kettle from going out and buying the biggest caravan in existance, and hitting the open road with it behind their Corolla, without so much as even towing a box trailer previously.

[Marakai]

Hmm, I guess those are actually fair enough points. Especially the utter lack of proper licensing/training of drivers in Australia as well as the lack of speed restriction (I go white-knuckled in anger when I see some dolts do 110 on the Calder with their 2-horse loaded trailers - what is WRONG with these people?! 2 minutes on Google will bring up stomach-turning photos of accidents with trailers - and what's left of the horse afterwards ).

I can also see the weight issue to a certain points: empty weight of the Alltrack is 1700 - but that's without *everything*, driver, pax, *fuel*! Once I get in with the missus, plus gear and petrol, the thing will push over 2 tons, and we're not overweight people by any stretch of the imagination! Meaning even if you use Bobba's Law ("never tow more than your vehicle weighs"), which is a good thing, it's a bit restrictive to use the fairly imaginary pure empty weight as a baseline.

[wai]

Every state/territory has limits on what can be towed, and they are all based on the UNLADEN weight of the tow vehicle and whether it is braked or unbraked. As an aside, I worked with someone who had a daughter who rode at a local pony club. He had to get a Landcruiser because a horse is heavy, and it was the only way he could get the horse around. Engine power was not the issue. He had a V8 Commodore wagon, but weight wise, it was not allowed to tow the horse and float around.

The reason the unladen weight is used is because that is the worst case scenario for towing when it comes to braking. Yes the weight to stop is lower, but then so is the available friction force between the tyres and road surface on the tow vehicles wheels. The friction force available is prportional to the weight over the braked wheels. The lower the weight, the lower the friction force (multiplied by the non-dimensional coefficient of friction).

On speed limits when towing, I can remember there used to be a rule where the speed limit was 80 km/h when towing. I don't believe there is a limit any more.

[Marakai]

While I understand the supposed underlying principle it flies in the face of actual *physics*!

Kinetic energy if proportional to mass, but proportional to *square* of velocity. Which means that if they were really about ensuring safety they would limit the speed of towing moreso than the weight.

Thus:
1800kg going 80km/h: 5,760,000 J
1800kg going 100km/h: 9,000,000 J (!)
2000kg going 80km/h: 6,400,000 J

Isn't that what all the "speed kills" is supposed to be about? Why is it not applied here? I know, I know, most pols wouldn't understand actual science if you drew them pictures in crayons. Just that for once I'd like to at least see some consistency.

Every state/territory has limits on what can be towed, and they are all based on the UNLADEN weight of the tow vehicle and whether it is braked or unbraked. As an aside, I worked with someone who had a daughter who rode at a local pony club. He had to get a Landcruiser because a horse is heavy, and it was the only way he could get the horse around. Engine power was not the issue. He had a V8 Commodore wagon, but weight wise, it was not allowed to tow the horse and float around.

The reason the unladen weight is used is because that is the worst case scenario for towing when it comes to braking. Yes the weight to stop is lower, but then so is the available friction force between the tyres and road surface on the tow vehicles wheels. The friction force available is prportional to the weight over the braked wheels. The lower the weight, the lower the friction force (multiplied by the non-dimensional coefficient of friction).

On speed limits when towing, I can remember there used to be a rule where the speed limit was 80 km/h when towing. I don't believe there is a limit any more.

[Amalgam]

Ooooh Science !!!!!

[wai]

Yes, but then you would never ever allow any truck on the road either. Just look at the energy of a 38 tonne semi travelling at 100 km/h! Don't even think about looking at the energy in a B-Double ir a B-Tripple.

But friction is not just related to stopping, although the information from the authorities do allow a higher trailer weight if brakes are fitted. It is controlability that is also an issue. Even negotiating a corner is an issue as without sufficient weight in the tow vehicle can see the trailer push the tow vehicle wherever it wants to.

On the speed kills campaign, this is purely political. They show the dramatic consequences of travelling at 65 km/h instead of 60 km/h. But look at the difference between 40 km/h and 50 km/h. Speaking of 40 km/h, it amuses me when I see a bus with the lights flashing but doing 60 km/h. I am supposed to slow to 40 km/h while the bus carries on at 60 km/h. Other quirks are where you can have route busses travelling full with seated and standing passengers (no seat belts) at speeds of up to 100 km/h, or the inconsistent speed restrictions on learners and P platers, and minimum driving age.

So, there is a lot of politics involved, however there are compelling reasons to relate the trailer weight to the tow vehicle weight, and to require trailer brakes over a specified weight. There is also a compelling argument to limit the speed of a vehicle when towing to say 90 km/h, but can you imagine the outcry if that were to happen?

[Marakai]

Well it's not about NEVER EVER, but rather it's about an acceptable speed. I don't subscribe to the Speed Kills nonsense, which you rightly ascribe to politics, as thinking that government logic to the end would see us all going back to early 20th century "the human body was not made for speed above 25km/h". Of course the nanny state won't be happy until we're all coddled in swaddling, as my wife likes to say.

Meaning, maybe trucks *should* be limited to 80! (and banned from the passing lanes, but that's just a personal peeve of mine). So should towing vehicles! Especially if transporting live animals.

You're also right about controlability, but that isn't just a function of physics, that's also a function of training and adaptive driving. Which admittedly are sorely lacking in Australia. (Having driven extensively over decades on 4 continents, I'm sad to state categorically that at the least Melburnians are amongst the worst drivers I've ever shared the road with ) Common sense is also absent - I just reamed a P-plater on a horse forum about wanting to know what SUV she should drive to tow her horses. A *P Plater*!

My point being that these vehicles quite obviously can safely tow according to the manufacturer's specifications in countries with higher speed limits but also with higher levels of training. So, it's as if the government recognises that Australians are horrid drivers and the only weapon they have in their arsenal is to muck about with the maker's ratings, as they either feel they have already lowered speed limits to what society will accept or can't be bothered to have a tiered system.

Oh well.

Yes, but then you would never ever allow any truck on the road either. Just look at the energy of a 38 tonne semi travelling at 100 km/h! Don't even think about looking at the energy in a B-Double ir a B-Tripple.

But friction is not just related to stopping, although the information from the authorities do allow a higher trailer weight if brakes are fitted. It is controlability that is also an issue. Even negotiating a corner is an issue as without sufficient weight in the tow vehicle can see the trailer push the tow vehicle wherever it wants to.

On the speed kills campaign, this is purely political. They show the dramatic consequences of travelling at 65 km/h instead of 60 km/h. But look at the difference between 40 km/h and 50 km/h. Speaking of 40 km/h, it amuses me when I see a bus with the lights flashing but doing 60 km/h. I am supposed to slow to 40 km/h while the bus carries on at 60 km/h. Other quirks are where you can have route busses travelling full with seated and standing passengers (no seat belts) at speeds of up to 100 km/h, or the inconsistent speed restrictions on learners and P platers, and minimum driving age.

So, there is a lot of politics involved, however there are compelling reasons to relate the trailer weight to the tow vehicle weight, and to require trailer brakes over a specified weight. There is also a compelling argument to limit the speed of a vehicle when towing to say 90 km/h, but can you imagine the outcry if that were to happen?