What is the REASON for towball weight?

[fishingrod]

Can someone explain the REASON for needing towball weight ?

Members on here will always be very quick to say how much towball weight a trailer should have, but i dont think ive even seen a explaination why. I know with a single axle too little towball weight can mean there is too much weight behind the axle and it will most likely fishtail. Ive previously towed many trailers. One was a 1500kg dual axle with only 30-50kg towball weight and it towed fine at up to 90-100km/h with no fish tailing.

I know it should typically be around 7-15% of the rigs total weight, but what is the reason for it. Is it to provide extra traction/grip to the tow car? Is it a legal requirement?

Look forward to the replies
Rod

[Roughasguts]

I guess if the tow ball weight is to light or even negative weight, and your going down hill and around a bend, and have to slam the brakes on.

Well the car is going to jack knife quite easily, but if theres some good weight there the arse end of the car is less likely to slide out. Same for towing in a turn.

[finga]

And if there is too much ball weight you end up with no steering or ineffective steering as the weight put on the rear end of the vehicle lifts the front wheels up.
You don't want that either.

[Noelm]

it would take a lot of towball weight to lift the front wheels, but the reason for the weight on the towball is to counter the effect of a balanced or rear heavy trailer that will start to sway and become almost uncontrollable at fairly modest speed, it all comes down to the simple thing that the further the wheels (of the trailer) are away from the tow point, the better it will tow, but this needs to be balanced with weight on the tow vehicle, no sense in have a great towing trailer, but the rear end of the car is dragging it's bum (like a dog with worms) and is not reasonable balanced. some of this can be offset by air bags and extra springs and so on.

[Wahoo]

also if your tow bar says max down weight is 120kg and you went over that 120kg and had an mishap insurance wont cover the car or boat

Daz

[Noelm]

I guess another way to describe the reason is to imagine a trailer off the car and perfectly balanced, if it where possible, you could give it a spin and it would just go around and around (like a toy top or a frisbee) but if it has the wheels moved back so the coupling is on the ground, try to spin it now!, I know it is a sort of bad example, but if you try really hard you might be able to imagine what I said (maybe)

[TOPAZ]

As mentioned above, the main reason is to minimise the tendency of the trailer to sway, which, if uncontrolled, can actually roll both the trailer AND the tow vehicle.
10% of the Gross Trailer Mass (includes both trailer and load), is the generally recognised rule of thumb for the MINIMUM, towball weight.

If this downward force causes the tow vehicle to sag at the rear/lift at the front, the ONLY way to properly correct this is to fit a LOAD DISTRIBUTING HITCH.


Richard.

[charleville]

I had an interesting experience 25 years ago when walking across a bridge across the Kolan river up Bundaberg way. I and a colleague were just at the end of the bridge when a station wagon towing a caravan approached the bridge at highway speed and the driver's side rear tyre on the station wagon blew out and the whole car and caravan did a 180 degree spin right in front of us, 5 - 6 metres away.

Luckily for the family in the car, the whole shebang stayed on the bridge as the bridge is a long way above the river.

My mate and I were there surveying a route for a work project adjacent to the bridge and after that incident he got such a shock and was really shaking, saying, "Ya know, the only casualties of that could have been us!" ;D That was very true - had we been a few metres further along the bridge, our only escape would have been a suicidal jump off the bridge. There were no mobile phones in those days and it was a long way from a telephone to get help.

Anyway, what I have pondered over and over for all of those years was just how a rear tyre blow-out on the tow vehicle made the whole rig spin through 180 degrees. My guess is that it happened because the driver slammed on the brakes but I have never understood the dynamics of what might have cause the spin. I often wonder if weight distribution caused it - or maybe bad brakes on the caravan - or whatever. :-/

[tunaticer]

The other reason why towball weight is important is because a trailer with near zero ball weight will be continually rocking back and forward creating lift in the rear of the car and down pressure on the other end of the swing. The suspension is designed to operate with positive downforce on the wheels to maintain traction and therefore safety.
If you have a trailerwith zero ball weight connected try towing it uphill in the wet. If the trailer is heavy enough you will not be able to get traction to move the trailer.

Jack

[Lovey80]

Imagine a trailer with negative towball weight........ ?You would have to have it hitched at all times otherwise it would sit on it's arse when it was unhitched. Prolly smack your Jaw loose too as you unhitched it. Waste of time having a jockey wheel then wouldn't it? Also the old stocko towball trailer hitch needs that weight bearing down on it to actually stay secure and turn at the hinge point. I like to have it so the trailer is liftable off the towball ie If the jockey wheel has the A frame level then it will be very easy to move without a car. In saying that my boat trailer/camper weighs 1300kg and im not lifting 130kg to lift it thats for sure and it tows fine.

Cheers Chris

[joeT]

Another reason for towball weight is, if for some reason the trailer gets disconnected from the car while travelling, the trailer would nose down and come to a stop quite quickly. Imagine with negative weight or perfectly balanced, the trailer would carry on down the road until it hit something (or someone).

[Kerry]

Gravity!!!!!!!!!!!

[fishingrod]

Thanks for the replies .... some good disscussion here.

It sounds like its probably a combination of good reasons to have the correct down weight.

But as Chris has pointed out, and i have experienced before, if its less than 10% some trailers can still tow comfortably

cheers
Rod

[Reef_fisher]

Not withstanding all of the above, if the ball and hitch become separated for any reason including not locking done properly the hitch (withsafety chain fitted!!) will drop down below the level of the back of the vehicle and not punch through the back of the tow vehicle will still remaining of the road and enable the driver to stop the vehicle with very little damage occuring to vehicle, trailer and anything else within the immediate location. Two chains are better( for balance) than one despite only one being needed by law.

Have seen the result of negative balance no chain and separation, this bloke was tired of have to hook up and then unhook all the time on ute, kids were sitting in the back of ute. Luckily was in caravan park, at about 5kph. Damage was enough to make me cringe. Luckily the kids on the back narrowly missed getting hit by the A frame of trailer. As the A frame slid up onto back of ute the outbourd dug into the bitumen. Fishing part of holiday over!!

[Sea-Dog]

I saw an incident where a bloke was towing a chip van (you know, the vans that sell hot chips at markets etc.)

The whole tongue of his towbar came off the tow vehicle. (Safety chain still attached to the tongue of course)

I was following behind this bloke going up a bit of a hill on a 6 lane divided road.

The van in front started to slow down, and gradually changed direction.

I changed lanes to go around him and then noticed that the van was on its own.

I just stopped, dumbfounded, watching what transpired.

The van stopped, then started back downhill. It ran over the median strip, went barrelling down the other side of the road.

It hit the gutter, jumped the footpath and went crashing through a blokes front fence and demolished his little garden shed. The bloke had only left the shed seconds before the van ended up on top of it.

No cars were damaged, no people were hurt. Bloody lucky is all I can say.

Perhaps safety chains shouldn't be attached just to the tongue of a towbar, but rather to the towbar itself.

[Sea-Dog]

Gravity!!!!!!!!!!!

You mean Kerry, because the Earth sucks. :P

[mako101]

I had a bit of a unnerving towing experience years ago with a trailer full of pavers behind a suzuki stockman going down a dirt hill, hit the brakes, trailer jackknifed sideways and actually dragged the car down a hill, lucky there were no sheer dropoffs as I had no control whatsoever, I guess the same could quite easily happen with a boat in the wet going downhill or taking a corner to fast.

Where boats are concerned though I have found top name brands best, I`ve owned homemade types and they are not as safe, not balanced right, but my current brooker is steady as a rock, usually so good I forget its on there, I would never own a homemade or cheaper/little known brand name trailer again.

[tunaticer]

I lost a trailer 20 yrs ago due to the old notched nut you turn to tighten it to the towball. The little spring loaded "bent nail" dog pin to stop it undoing snapped off where it was bent as i was driving. Sometime in the next 600km of that drive the trailer came off and the hitch hit the corrugated dirt road and dug in snapping the chain and standing the trailer temporarily on its nose before careering off the side of the road into the trees. The chain was 1/2" galvanized chain so that should have held without breaking but i suppose if its yanked like that almost anything will part. there were 3 links and a 5/8" shackle still on my car and the rest of the chain bar the broken link on the trailer.

There wasnt too much damage done really got the trailer back on the ball and tightened it down and hit the threads with a hammer and cold chizel so it wouldnt come undone again. A bit of fencing wire linked thru the chain 4 times and twisted off got me home.

Jack.

[northernblue]

Tunaticer, making a play for Australian of the year with the fencing wire.....how was your radio reception?

[freefish]

I understand that it is because towbars are now rated for maximum towing weight & towball weight is a % of this. Also figured into carrying capacity of vehicle i.e. station sedan loaded to gills with camping gear would have little leeway on tow ball weight for boat. Loading camping gear into boat increases towball weight & can still go over limit. Am told NSW getting pretty savage on this. Bill

[tunaticer]

Northernblue, The radio reception was fine but the colour of the air in the cabin was pretty blue if i remember correctly. Even the dog didnt look at me for a month.

Jack

[seabug]

As mentioned above, the main reason is to minimise the tendency of the trailer to sway, which, if uncontrolled, can actually roll both the trailer AND the tow vehicle.
10% of the Gross Trailer Mass (includes both trailer and load), is the generally recognised rule of thumb for the MINIMUM, towball weight.

If this downward force causes the tow vehicle to sag at the rear/lift at the front, the ONLY way to properly correct this is to fit a LOAD DISTRIBUTING HITCH.


Richard.

And it is surprising how little weight at the back can cause trouble.

I once had to get a 7m lenght of 50mmx100mm for the farm and only had a 6ftx10ft tandem trailer to cart it.

It travelled OK for about 20km at 100kmph and then suddenly got the Valiant and trailer swaying violently all over the road.
Came very close to losing the lot.
Amazing what can happen in a couple of seconds.

Regards
seabug

[Eagle]

I tried to post this yesterday but had no success. It should work this time. My apollogies if this has already been written by someone else.

The reason for having weight on the tow-ball is that the Centre of Gravity of the trailer and boat must be forward of the axle for the rig to be stable. If the CG is behind the the axle, the trailer will commence to sway and the occilations will grow bigger each time the trailer passes from one side to the other. A dual axle trailer will also still try and sway. The dynamics for swaying are lessend because of the four tyres. A dual axle should have some load bearing on the towball for best stability. Having the CG just forward of the centre of the dual axles will give the best load balance
If the CG is behind the axle (a single axle) and you brake suddenly, the load (mass) will shift to the side and jack-knife the rig. This is why you also need good tread on your trailer tyres. As mentioned earlier, if 10% of the weight makes the rear of the car sag, then fitting Load Leveller Bars will fix the problem. These bars keep the car level and maintain the correct load on all four wheels of the car.
My father and I towed our 18 footer to Bairnsdale a long time ago and the winch pillar snaped off. The boat rolled back about four feet on the trailer and the trailer started to sway uncontrolably. The only way to stop the osscilations was to accelerate when the trailer was aligned on the certerline of the car. We were towing at 95k/h. When the swaying stopped, very gentle braking slowed us down to a safe stop. It took about 2 miles to achieve the safe stop as some acceleration was needed to again control the swaying. It was quite a hairy time.

Eagle