Never towed a van and got scarred by snaking!

[JTQ]

Never felt the ATC come on either.

Now that in my circumstances would bug me, as I said I like to be aware it actually works.
Its sensitivity to intervene, coupled with our 1.9 tonnes, 8 metre long van on a single axle, means it does quite frequently, probably every other trip.

Stability wise the unit is excellent, it has 3.25 tonnes of towcar, but the van sways nevertheless, doing that is inevitably with the dynamics of travelling along winding routes.
Even at walking pace on an undulating rally field it can be activated, as well as the more usual disturbance exiting tight roundabouts.

 

[Jcloughie]

I don't know how you can say that the speed was not unreasonable. To make my point, take an extreme example. A snake will never occur at walking pace, no matter how badly loads are distributed. Not that I'm saying that one should tow at walking pace, but it's a sliding scale. Somewhere between walking pace and motorway speeds instability can become a issue and it's up to the driver to sense the point where things become uneasy and one needs to make sure that speed is not exceeded. The only exception that I can see where one could be caught out is if something really unexpected happens, such as a sudden bout of crosswind or a forced evasive manoeuvre. However, those would be isolated incidents and would not explain general nervous or twitchy towing.

I agree, I remember once towing down to Dover. I had two weeks of rock steady towing. So I guess my outfit and balance were fine. But on my most hated road, the M25, I got a bad snake. I imagine brought on by buffeting. Totally isolated incident. But not nice.


John

 

[ProfJohnL]

JTQ has effectively raised the question of what is a snake? each of us may have a different take on the details or how extreem the movement has to become to be called a snake. but in this case there has been an independent arbiter which has has taken some of the guesswork out of the question. The operation of the ATC.

Both Hutch and JTQ have pointed out that the ATC can operate momentarily on occasions, but the OP's report indicated the ATC had to intervene for a sustained period and it reduced the outfits speed by over 10mph. That is a very significant intervention which would only be a response to a significant snake like event.

Lutz as questioned my phrasing the OP's speed "was not unreasonable" I phrased it that way to acknowledge the OP was apparently driving sensibly before the event occured.

What is clear though, after the trigger event, the outfit was not self correcting, and that's why the ATC kicked in. This suggests the outfit must have been on the the edge of instability at normal road speed.

If Outdoorguy hadn't had ATC the situation may not have been saved.

 

[Jcloughie]

Never felt the ATC come on either.

I regularly will feel it bite, often on a round-about as the direction changes. I find it very satisfying to know it's working.

John

 

[Bluetonic]

Maybe I need to tow a bit faster then 🤷‍♀️

 

[JTQ]

how extreem the movement has to become to be called a snake. but in this case there has been an independent arbiter which has has taken some of the guesswork out of the question. The operation of the ATC.

Not a conclusion I can accept, the ATC only detects swaying, involving accelerations and possibly the number of cycles involved; not published figures I am aware of.
It does not know if that will be sustained or where it might go; so simply it intervenes as way the safest action without the "brain power" for deeper analysis of the changes. It does not even know the road speed, as discussed, a big factor.

Any number of things can set up a few cycles of sway; by my definition that is only a "snake" if the magnitudes of accelerations etc start building up, not if they are destined to naturally decay.

 

[outdoorguy]

Wow, lot of posts! Thank you for your time! I don't have much to add. The most of the things were on the axle, only 'heavy' thing in the tail was the flushing toilet - 5 liters or so.
If it was ATC, I dont know. Quick read here: https://www.ukcampsite.co.uk/chatte...ds.asp?ForumID=20&TopicID=143357&ThreadPage=1
suggest that it could be my Honda - I felt braking in the front.
I would say that my case if it was snake, it was 'dampening oscillation' - gust could hit tail of the trailer and indeed cause snake, but even without car/trailer assistance I suppose it would damp itself due to loading distribution. As per YT video several posts above.
I am quite relaxed about the incident, as it wasn't self-induced. And during rest of long journey (total of 250 miles), I havent got close to 'tail wagging'. Also, it did not felf worse than pulling toward coach, which happened several times during this trip.

As I said, I am taking loading very seriously, and there are no heavy items except flor near axle in the van when I tow.

 

[Lutz]

I'm a bit surprised at the reports of ATC cutting in quite often and quite strongly in some cases. That would suggest that the feature is a little oversensitive. It would be interesting to know what algorithms AlKo employ in the deployment of their system. I had a LEAS stabiliser on my previous caravan. It works on the same principle as AlKo's ATC and that was set to act when the lateral acceleration exceeded 2m/s² over 2 full cycles and it then applied 10% of full braking performance. I think that in the course of the 5 or 6 years that I had it, it certainly didn't deploy more than half a dozen times. I would only know that it had deployed because the LEAS system included a buzzer in the towcar to warn the driver when it operated. There was never a noticeable tug at the towbar.

 

[JTQ]

I regularly will feel it bite, often on a round-about as the direction changes. I find it very satisfying to know it's working.

John

That John nicely describes the effect. a momentary but still evident check; there and gone, no clamping on and maintaining for any noticeable period ground anchors.

If I recall correctly the discussions at various times in 2007/2008 with engineers at Alko [who in 2008 later installed ours], the installer aims to set things to apply 40% braking. Noticeably at x4, higher than Lutz's LEAS installation, whether I would also sense that much reduced "checking" I don't know?
Others over the years had said it has pulled the speed way down stating it needs brake warning lights. I never have anything remotely like that, as said just enough to be aware it had applied a small check. I suspect elsewhere there had been some poorly set installations.

 

[Dustydog]

In 16 years with ATC I have only ever felt a minor tug a handful of times . A moment in time. ATC is not a “OMG ATC saved my life”.

ATC constantly monitors the caravan swing and, if it detects that sideways movements are increasing rather than decreasing, it pulls the trailer brakes on briefly bringing the caravan back into line. It will not react to sudden movements that self-correct or in normal cornering.
Prof, I have to ask if you have actually experienced ATC in operation?
In my experience ATC kicks in long before a full blown snake happens. If the snake develops the driver hasn’t taken foot off the throttle or the ATC is faulty.
Any unit will drop speed rapidly if the throttle is released. It’s possible the over run brakes kicked in , not ATC.

 

[Buckman]

In 16 years with ATC I have only ever felt a minor tug a handful of times . A moment in time. ATC is not a “OMG ATC saved my life”.

ATC constantly monitors the caravan swing and, if it detects that sideways movements are increasing rather than decreasing, it pulls the trailer brakes on briefly bringing the caravan back into line. It will not react to sudden movements that self-correct or in normal cornering.
Prof, I have to ask if you have actually experienced ATC in operation?
In my experience ATC kicks in long before a full blown snake happens. If the snake develops the driver hasn’t taken foot off the throttle or the ATC is faulty.
Any unit will drop speed rapidly if the throttle is released. It’s possible the over run brakes kicked in , not ATC.

TBH I think that if you remove your foot quickly off the accelerator during a snake, it may make the snake worse as the engine is then braking the outfit. I am a believer is slacking off and then gentle acceleration to straighten the outfit. Unfortunately I speak from experience even if it was one time and the vehicle was a lot heavier than the MTPLM of the caravan.

 

[ProfJohnL]

In 16 years with ATC I have only ever felt a minor tug a handful of times . A moment in time. ATC is not a “OMG ATC saved my life”.

ATC constantly monitors the caravan swing and, if it detects that sideways movements are increasing rather than decreasing, it pulls the trailer brakes on briefly bringing the caravan back into line. It will not react to sudden movements that self-correct or in normal cornering.
Prof, I have to ask if you have actually experienced ATC in operation?
In my experience ATC kicks in long before a full blown snake happens. If the snake develops the driver hasn’t taken foot off the throttle or the ATC is faulty.
Any unit will drop speed rapidly if the throttle is released. It’s possible the over run brakes kicked in , not ATC.

Yes I have when a friend was driving, and in my opinion driving too fast. But personally never whilst I have been driving.

 

[Dustydog]

Yes I have when a friend was driving, and in my opinion driving too fast. But personally never whilst I have been driving.

No ATC application?

 

[otherclive]

Wow, lot of posts! Thank you for your time! I don't have much to add. The most of the things were on the axle, only 'heavy' thing in the tail was the flushing toilet - 5 liters or so.
If it was ATC, I dont know. Quick read here: https://www.ukcampsite.co.uk/chatte...ds.asp?ForumID=20&TopicID=143357&ThreadPage=1
suggest that it could be my Honda - I felt braking in the front.
I would say that my case if it was snake, it was 'dampening oscillation' - gust could hit tail of the trailer and indeed cause snake, but even without car/trailer assistance I suppose it would damp itself due to loading distribution. As per YT video several posts above.
I am quite relaxed about the incident, as it wasn't self-induced. And during rest of long journey (total of 250 miles), I havent got close to 'tail wagging'. Also, it did not felf worse than pulling toward coach, which happened several times during this trip.

As I said, I am taking loading very seriously, and there are no heavy items except flor near axle in the van when I tow.

It’s not a certainty that the “snake or sway” would self damp if the car did not have trailer assistance, the caravan did not have ATC. All you would have to provide a damping input is the Alko hitch stabiliser. When coaches or big trucks or even faster moving outfits come from behind it’s a good idea to move left in your lane. It reduces the sideways pull.

 

[Lutz]

TBH I think that if you remove your foot quickly off the accelerator during a snake, it may make the snake worse as the engine is then braking the outfit. I am a believer is slacking off and then gentle acceleration to straighten the outfit. Unfortunately I speak from experience even if it was one time and the vehicle was a lot heavier than the MTPLM of the caravan.

ATC does no more than apply the caravan's brakes. If you don't have ATC then lifting the foot off the accelerator has the same effect. The caravan will try to push the car enough to automatically apply the overrun brake which is what the ATC would otherwise do. Both methods work except that the latter requires active intervention on the part of the driver.
Taking the foot off the accelerator doesn't make a snake worse. Only fierce application of the car's brakes could do that.

 

[JTQ]

ATC does no more than apply the caravan's brakes. If you don't have ATC then lifting the foot off the accelerator has the same effect.

Which completely misses the point that with the ATC acting the hitch is in tension, whereas to activate the over run the hitch, it is in compression, that's the principle how it functions.
With ATC it is the car dragging the caravan into line that tames the swaying. You can't drag the trailer with its coupling in compression.
Far from the "same effect".

 

[Kevin M]

Probably already been said but, with experience, you realise that the van will move about.
Our car / van match is just over 50%, still feel the odd white van passing, still feel a gusty side wind, still feel the tram lines in the road surface, keep the speeds down and relax into it.
I used to race classic bikes off road, with experience, you learn to not hold on too tight and let the bike move about under you, I view towing the same..it will move but try not to over compensate.
All comes with experience.

Kev

 

[Lutz]

Which completely misses the point that with the ATC acting the hitch is in tension, whereas to activate the over run the hitch, it is in compression, that's the principle how it functions.
With ATC it is the car dragging the caravan into line that tames the swaying. You can't drag the trailer with its coupling in compression.
Far from the "same effect".

But the overrun brake will pull the caravan straight until such time as the caravan has slowed down more than the towing vehicle. Once both have slowed down enough, the caravan will recover and return to a stable condition of its own accord without the need for any external action. If that weren't the case it would be impossible to regain control of a swaying caravan if ATC is not fitted.

 

[JTQ]

Once both have slowed down enough, the caravan will recover and return to a stable condition of its own accord without the need for any external action.

In that lies the issue, and why it is not the "same effect", the time things are unstable, so at risk. With the ATC [or LEAS] exploiting the car's pull, and the whole unit slowing, stability will be achieved more quickly.
Plus, it requires no driver involvement and thus skills.

 

[Hutch]

When the ATC activates after normally 2, Very rapid but short lateral sways, , the trailer brakes activate quickly ( within second or 2) and the trailer brings the whole unit into line and in my case reduced the speed by 10 mph.
Unless you have experienced a Sway and a potential snake. It is hard to explain the difference. The smell in the car tells the difference.

 

[Buckman]

ATC does no more than apply the caravan's brakes. If you don't have ATC then lifting the foot off the accelerator has the same effect. The caravan will try to push the car enough to automatically apply the overrun brake which is what the ATC would otherwise do. Both methods work except that the latter requires active intervention on the part of the driver.
Taking the foot off the accelerator doesn't make a snake worse. Only fierce application of the car's brakes could do that.

In this case the caravan in 2004 never had ATC.

 

[Dustydog]

Whilst this is not restricted to snakes it is interesting.
https://uk.motor1.com/news/351308/trailer-accidents-safety-uk-motorways/

 

[Buckman]

Whilst this is not restricted to snakes it is interesting.
https://uk.motor1.com/news/351308/trailer-accidents-safety-uk-motorways/

Pity there is nom breakdown of the statistics as wonder how many caravans are actually involved in mishaps. Trailers probably covers all trailers including trailers towed by HGVs.

 

[otherclive]

Pity there is nom breakdown of the statistics as wonder how many caravans are actually involved in mishaps. Trailers probably covers all trailers including trailers towed by HGVs.

I posted a breakdown of the statistics for trailer accident a while back. It came out of a comprehensive HoC report with contributions from emergency services, insurer, DVSA, Caravanning bodies etc. post #48 in the link refers.

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https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/940182/trailer-safety-statutory-report-web.pdf

 

[Buckman]

I posted a breakdown of the statistics for trailer accident a while back. It came out of a comprehensive HoC report with contributions from emergency services, insurer, DVSA, Caravanning bodies etc. post #48 in the link refers.

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https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/940182/trailer-safety-statutory-report-web.pdf

Thanks. According to those statistics for the year prior to 2019 when the report was published 158 caravans were involved in accidents where there have been 11 injuries or fatalities. . That is less than 1 a day.

Interestingly the majority of breakdown not accident incidents involved tyres.