Weight Question

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Originally Posted by DiscoMick

The dynamics of this are very interesting, and a bit of a mystery to me, so I'm learning from this thread.
The point about semi-trailer and other trucks towing multiple times the prime mover weight certainly shows that a vehicle can tow much more than its own weight if it is set up right.
On trailers, an interesting example is that our camper trailer has, according to the manufacturer, a weight of about 1600kg and a towball of 140kg. However, they offer a extra 100 litre water tank which can be attached to the rear behind the spare tyres. They say adding that 100 litre tank reduces the towball from 140kg to 110kg. So it's interesting to see the effect of where the weight is placed.

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The semi-trailers dynamics are totally different to a car that is towing, the whole design is just so different and in reality they are not comparable.

For water tanks, I think the best place for them is over the axle and definately not behind the axle.

https://www.youtube.com/watch?v=6mW_gzdh6to

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Originally Posted by Graeme

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Just a "Turn of Phrase", Graeme. No malice intended.

If static overloading is taken into account by the manufacturers , as explained above by Blknight, then would or would not the same physics apply to the OP's query?
Like others on here, my physics rationale is somewhat lacking.[bigsmile1]

Thats just wrong Slunnie,, in so many ways.
all it is is an advertising gimmick to sell stuff, scaremongering at its worst.

in all of history nothing has ever been built where the axle is in the middle of the tow length. not even box trailers.


to give an example,, my 30 year old Golf is 4.2m from hitch to the centre of the axles,, and then only another 2.5m to the number plate.
and mine has what I consider a short A frame....


someone somewhere build a toy with those dimensions!! :soapbox::soapbox::soapbox::soapbox:

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Originally Posted by Pedro_The_Swift

Thats just wrong Slunnie,, in so many ways.
all it is is an advertising gimmick to sell stuff, scaremongering at its worst.

in all of history nothing has ever been built where the axle is in the middle of the tow length. not even box trailers.


to give an example,, my 30 year old Golf is 4.2m from hitch to the centre of the axles,, and then only another 2.5m to the number plate.
and mine has what I consider a short A frame....


someone somewhere build a toy with those dimensions!! :soapbox::soapbox::soapbox::soapbox:

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I disagree with that, it's given a really good physics demonstration there. Its not about the axle being 20% further forward or rearward, its a demonstration of how the loading will influence the stability of the trailer. If anything that design is emphasising the situation for the sake of demonstration, but the take aways from that demonstration are still exactly the same, which is not to place the load masses to the rearward extremity otherwise it will induce wagging. We all know that trailers can get the wags on, especially caravans which have long rearward overhangs with weight on the ends and this demonstration is showing what that can do.

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Originally Posted by Saitch

Just a "Turn of Phrase", Graeme. No malice intended.

If static overloading is taken into account by the manufacturers , as explained above by Blknight, then would or would not the same physics apply to the OP's query?
Like others on here, my physics rationale is somewhat lacking.[bigsmile1]

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I'm not familiar with the phrase so didn't and still don't know what you meant.

Momentary or cyclic extra load on the tow-bar due to forward/aft rocking on undulating surfaces is not static load and therefore doesn't breach a static load limit, even though I think it is unlikely that LR tested extreme possibilities of vans on badly undulating surfaces and therefore damage to the tow vehicle could occur. Long tow couplings, such as the one that I use on my L322 to clear the bumper, could be a legal issue because LR's maximum ball weight specifications include the maximum distance of the ball from the retaining pin.

its actually a really bad physics demo,, it has NOTHING to do with the real world.

as stated. Its design premise was to SELL stuff,, ( I saw this demo 30 years ago at the Brisbane Ekka, at an aftermarket/accessory display)
its designed to actually SCARE people into buying goods.

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Originally Posted by Pedro_The_Swift

its actually a really bad physics demo,, it has NOTHING to do with the real world.

as stated. Its design premise was to SELL stuff,, ( I saw this demo 30 years ago at the Brisbane Ekka, at an aftermarket/accessory display)
its designed to actually SCARE people into buying goods.

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The machines axle line can be moved, I’ve seen the display also, and they moved it around.

Still an excellent display of the physics in action.

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Originally Posted by dirvine

On another web site, it is claimed that when you put a towball weight on your car (does not matter what the weight is) weight comes off the front of the car and as such more than the tow ball weight is added to the rear axle load. The quote is much like the fulcum on a see saw. What has been quoted is that a ball weight of 350kg means about 500kg is loaded onto the rear axle. I failed physics so I am unsure if this is correct. If this is the case then I question if any car could tow a 3.5T van with a notional ball weight of 350kg. Can any of you gurus here answer my question in simple terms. I dont know how you can accurately guess the tare weight on a rear axle unless you drive over a weigh bridge, so just halving the Tare weight would not give an accurate figure, or so i would deduce as I would think more weight would be biased to the front due to the engine and gearbox being more located to the front of the vehicle.Thanks David

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Hi David

if you know your ball weight then this simple calculation will tell you what weight will be added to your rear axle.


To calculate the actual ball weight affect on the rear axle; multiply the ball weight by the (vehicle wheelbase plus the rear overhang) and then divide the answer by the wheelbase.
cheers
David

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Originally Posted by Tombie

The machines axle line can be moved, I’ve seen the display also, and they moved it around.

Still an excellent display of the physics in action.

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Sometimes when you're trying to find the subtle cause of a cascading problem or you're pressed for time to get to the root cause of an issue it is very helpful to go to an extreme to see what happens.

I don't see that vid as even being close to extreme. It just shows a cause and effect very simply.

DL

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Originally Posted by dirvine

On another web site, it is claimed that when you put a towball weight on your car (does not matter what the weight is) weight comes off the front of the car and as such more than the tow ball weight is added to the rear axle load. The quote is much like the fulcum on a see saw. What has been quoted is that a ball weight of 350kg means about 500kg is loaded onto the rear axle. I failed physics so I am unsure if this is correct. If this is the case then I question if any car could tow a 3.5T van with a notional ball weight of 350kg. Can any of you gurus here answer my question in simple terms. I dont know how you can accurately guess the tare weight on a rear axle unless you drive over a weigh bridge, so just halving the Tare weight would not give an accurate figure, or so i would deduce as I would think more weight would be biased to the front due to the engine and gearbox being more located to the front of the vehicle.Thanks David

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David I cannot see the logic in a statement that putting 350 kgs on the towball means adding 500kgs added to your vehicles weight! Some manufacturers place load carrying reductions greater that the added towball weight when attaching a trailer but I have not seen any similar statement on this by Landrover so I am sure it does not apply in your case. All weights added to a vehicle have to take into account your vehicle GVM, axle loads front and rear and the important GCM of vehicle and trailer combined. GVM means Gross Vehicle Mass or total weight you vehicle can carry legally with front and rear axle loads equal this weight. GCM meaning total weight of the vehicle and trailer be as a maximum weight to be legal on Australian roads.