You need to watch the whole video Grind your teeth but watch it to the end then you should See why i watch that guy. You also know where i pick insider information up. Like that boat was to far back not incorrect laden on top of it all. can you spot how i got this information. https://www.youtube.com/watch?v=eQUt5FMPa64&t=25s
marte,
Dec 22, 3:37pm
I had a trailer overtake me & then do the towing once, when harmonics set in at 80km/h. Jack knifed 3 times alternately before doing a 180° sideways spin pivoting around the towball down the centreline of a main highway at 1am. Put put 4 pairs rubber marks on both side of the road at the same time, sideways.
s_nz,
Dec 22, 5:11pm
For those that don't feel like watching the video, the "insider info" is;
"I was one of the two tow truck drivers who recovered the boat. The boat had moved back on the trailer. (The winch support had come loose and slid back.) The owner had said every time he got close to 100km/h the car would start to wobble. The vehicle combo was also not weight balanced correctly." - Douglas Miller
That dosn't paint the driver in a good light. He / She was aware of dynamic stability issues with the rig, and not only did not investigate & resolve the issue, but also did not drive conservatively to get home. If you rig goes unstable at 100km/h, stay under that speed FFS. Definitely do not overtake multiple vehicles on downhill stretches of road.
Most here will be aware that the front / rear weight balance of car trailers is critical for stability. Need to have a decent chunk of weight as down-force on the tow bar. Heaps of youtube model car on treadmill video's to prove it.
Normally 10% of the total weight being tow ball down force is the rule of thumb (this comes from Aussie / america), but many vehicles (especially euro's, and euro market targeted run lower numbers, often between 4 -5%.
The way I understand it every towing rig has has a critical speed where it will go unstable (when disturbed by something like a road undulation nose wind from a truck). Trailer nose-weight is a big factor, but also the relative weights of the trailer to tow vehicle, distance of tow coupling from rear axle, how close the weight in the trailer is to the axle etc.
In the USA, and Aussie generally towing is done at fairly high speeds, requiring relatively high nose weights to maintain stability.
Speed limit in aussie for towing is often 100km/h, and in for example Washington state it is 60kmh (98km/h).
In Europe generally the speed limit for trailers over 750kg is generally 80km/h
NZ is kinda in between at 90km/h.
But in any area, you definitely want to avoid zero or negitive ball weight's. Very hard to save a swaying trailer if it happens on a steep downhill and you don't have the ablity to independently apply the trailer breaks.
tweake,
Dec 22, 5:44pm
how stupid do you have to be to know you have unstable load above a certain speed, the try to overtake at that speed or more.
i've had it a couple of times. one we where not going far and simply drove at 80kmh. the other was a shit hire trailer that after two attempts to fix it, just drove at 70kmh. fortunately very light traffic.
had multiple times where it got the shakes and accelerating just makes it worse. dab on the brakes to get the trailer brakes to kick in and loose some speed down to no shake speed.
Motorists drive this speed and more in other parts of the US even with the 55 limit.
intrade,
Dec 22, 7:25pm
Re #4 the same people drive like maniacs with the mazda bt 50 utes. and complain that something is weird with the tyres or suspension . Fact is that's not the tyres or suspension that's the stability control.After stability control comes the grim reaper. So that guy probably had that boat sway back and forward all the time since he tows it and nothing bad happened so it must be all normal and they just ignore things . Because the media told them they are save with airbags and stability control.
scuba,
Dec 22, 8:10pm
what it shows is the "Auto expert" spent 13 minutes in the original video wanking on about his ideas why the crash happened only to have the towie comment on his post the real reason. Boat shifted/ unbalanced load. This is the issue with "experts" making assumptions when they don't have all the facts. If this is your go to guy for auto information you may need to look further afield.
mrcat1,
Dec 22, 8:18pm
Speed is irrelevent! It comes down to the tow vehicles weight and the trailers weight, and how much weight transfer is on the towbar tongue. Youll find on most bars here there is a limit of 80-100kgs, thats fine to tow with.
intrade,
Dec 22, 8:42pm
like i said he is about 70% correct and i like the comedy he hates vw but only because vw in $hitswille dont honor the cga or AAA something in stralia. mingmoles and electric jesus is great fun to watch lol.
tweake,
Dec 22, 8:55pm
nah. higher speed requires higher towbar weight. usa is typically 15% of trailer weight due to higher speeds. there is an article around on the subject.
He hasn't got time for you tube anymore lol " ok i frequently go or did go to countrys for training in automotive diagnostics. England - gemany . australia all country i visited to take courses and my cash money comes from there. intrade (443 443 positive feedback) 10:26 am, Tue 22 Dec #9"
mrfxit,
Dec 22, 10:01pm
" He / She was aware of dynamic stability issues with the rig, and not only did not investigate & resolve the issue, but also did not drive conservatively to get home. If you rig goes unstable at 100km/h, stay under that speed FFS. Definitely do not overtake multiple vehicles on downhill stretches of road. " THAT bit ^^^ says the load/ balance & speed issue causing the crash, was actually nothing to do with "the load/ balance & speed issue". It's pure driver error. They had previous warnings but chose to ignore it & indeed decided to go faster (Not helped by passing other cars on a downhill section of road)
mrfxit,
Dec 22, 10:10pm
Downhill sways would have to be the hardest of all sways to regain control. Go faster = downhill will need extra speed AND an increasing amount for the duration of the slope. Steady speed for the slope duration (engine braking & "maybe" the slightest touch of the brakes depending on how bad it already is) & a very tight hold on the steering wheel in a straight line, should get you through it ok if it's not already too late to control it. Attempting to counter correct the sway just put's the entire rig under more stress.
Flat road swaying is a lot easier to sort out. Same for uphill swaying. Accelerating out of a sway & succeeding, MUST be followed by a major reduction in speed.
s_nz,
Dec 22, 10:28pm
Yes nose weight is important, but speed is very relevant to trailer stability. More nose-weight simply increases the speed at which the rig will go unstable.
If you want to see some experimental data, take a look at page 477 here:
They built a trailer to simulate a caravan with adjustable nose weight, with the properties to replicate a 880kg caravan, and towed it with a mondeo.
As you can see the damping ratio declines in a roughly linear manor as speed increases. As such the authors were able to extrapolate the data and determine the speed where there would be zero damping. Anything above this speed any disturbance will cause problematically increasing sway.
In their experiment they estimated the trailer with -0.84% nose weight went unstable at 90km/h, with 3.7% nose weight went unstable at 100km/h, and with 10.5% nose weight went unstable at 108km/h.
Note that this experiment would have different results with different to rigs. A heavy tow vehicle with wide tires and a short rear overhang like a land cruiser 200 would increase the damping, as would a trailer with the mass near the axle, rather than the ends.
With that particular tow rig, one could get away with the (far to low) -0.85% nose weight), if traveled comfortably under 90km/h (say at 85km/h). But if speed exceeded 90km/h we would likely see what happened in the video.
I think it's wrong to say that most bars have an 80 - 100kg downforce limits. My SUV has a 150kg limit, and most of the thai built utes have 350kg down-force limits on dealer supplied bars.
That said, those limits are common on on euro vehicles, and others. For example the mazda cx-5 petrol has a 80kg downforce limit, and a 1800kg tow limit (4.4%).
You are right that these limits are fine to tow with, but only under the basis that the heavy trailers are carefully loaded to near max towbar downforce, and that the rig does not speed (especially downhills). Using the data from the experiment above, the nose wight percentage of the cx-5 would go unstable at just over 100km/h. Quite fine if one sticks to the legal limit of 90km/h.
Note that much of the low nose-weight setups for sale in NZ are tested in the euro market where 750kg+ towing speed-limits generally max out at 80km/h. Also note that many cars (Ford Falcon, Ford territory, all Subaru's) in aussie at least have a 80km/h max towing speed in their manuals when towing their limit.
mrcat1,
Dec 22, 11:55pm
You still have it wrong! You are concentrating on drawbar load and speed, that is only two element's to keep a trailer on the road.
mrfxit,
Dec 23, 7:05am
Out of all this information, there are only two mistakes that count in this specific video.
Excess speed for the load conditions (not specifically critical) Passing other vehicles on a downhill road section (Critical mistake)
mrfxit,
Dec 23, 7:20am
The problem with debating what was the likely specific's of this accident, is that every combo of trailer/caravan/boat load & tow vehicle has it's own issues. You can narrow down a few specific's if you compartmentalize the possible combo's to examples like . . Trailer/caravan/ boat size Tow vehicle suspension type Load balance on the trailer/caravan/boat Overall combo length Tow vehicle weight FWD verses RWD
Then comes in potential speed for starting a sway.
At an educated guess, sways would normally start at about 60kph for a seriously bad combo & upwards from there. An average sway speed for most combo's would be about 80kph for the average domestic driver unexpected sway & upwards in speed from there.
john1623,
Dec 23, 8:43am
How would the towy know that the boat had slipped back prior to the crash. Think about it.
mrfxit,
Dec 23, 9:20am
Possibly because he's seen the same exact problem many times before. Still an assumption but a likely cause
s_nz,
Dec 23, 9:38am
Experimental data i quoted above had the rig going unstable at 90- 108km/h. While things like a heavier trailer could have an impact, I would hope that most tow rigs are set up so their sway speed is 100km/h+, comfortably above our towing speed limit of 90km/h.
I havn't run the numbers, but I suspect the most common heavy load in NZ (boats) have a longer axle to draw-bar distance and lesser rotational yaw inertia which should have the sitauation a little better than a caravan.
amasser,
Dec 23, 12:52pm
Mrs. Gump said it.
laurelanne,
Dec 23, 1:02pm
I remember reading an article with Peter Brock being interviewed, when he was asked about his scariest moment on the track. He said it was actually towing a race car back from Bathurst on night. Coming down a long hill the trailer started to sway. By the time he got to the bottom he was using all four lanes to hang on to it. Just shows, it can happen to the best of them.
tweake,
Dec 23, 2:51pm
however what throws a spanner in the works is in nz manufacture ratings are not legally binding. its recommended you follow the manufactures specs but your not legally required to do so.
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