Vehicle loading
Discussion
dilbert, I think you might be onto something here....
(and awesome diagram btw - how did you post that??)
I think we're all in agreement that if this was a Physics/Statics experiment in some lab, the axle weights would add up to the total weight, but in this real life/weighbridge situation there is some other factor that causing the discrepancy. As I said in an earlier post, if all four wheels of the van had been weighed separately but at the same time, the Plod would have had a different result, and surely that's not fair!!
So, I suppose the £64,000 question is
can the charge be challenged on the grounds of this discrepancy?
p.s. Cheers all for the efforts in posting to this forum, and special thanks also to chrisgr31's wife and work collegues for putting up with his experiments!!
(and awesome diagram btw - how did you post that??)
I think we're all in agreement that if this was a Physics/Statics experiment in some lab, the axle weights would add up to the total weight, but in this real life/weighbridge situation there is some other factor that causing the discrepancy. As I said in an earlier post, if all four wheels of the van had been weighed separately but at the same time, the Plod would have had a different result, and surely that's not fair!!
So, I suppose the £64,000 question is
can the charge be challenged on the grounds of this discrepancy?
p.s. Cheers all for the efforts in posting to this forum, and special thanks also to chrisgr31's wife and work collegues for putting up with his experiments!!
I think you can kick the ramp aspect into touch.
Looking at my old Motor Patrol Officers Notes it clearly states
" Be wary of any slope at the beginning of the weighbridge. If the front wheels start to climb the slope the rear axle weight will be greater than the true weight and if it is downhill slope the weight will be less."
Two defences mentioned. It is permitted to be overweight if proceeding to the nearest available weighbridge to weigh and if overweight to the nearest available place to offload the extra. A second dfence mentioned is where the weight has increased by up to 5% but no one has added anything to the load. eg vehicle loaded with dry sand, left in heavy rain storm so that load absorbs moisture.
Finally the person directing the driver to the weighbridge and weighing - was he an authorised officer?
dvd
Looking at my old Motor Patrol Officers Notes it clearly states
" Be wary of any slope at the beginning of the weighbridge. If the front wheels start to climb the slope the rear axle weight will be greater than the true weight and if it is downhill slope the weight will be less."
Two defences mentioned. It is permitted to be overweight if proceeding to the nearest available weighbridge to weigh and if overweight to the nearest available place to offload the extra. A second dfence mentioned is where the weight has increased by up to 5% but no one has added anything to the load. eg vehicle loaded with dry sand, left in heavy rain storm so that load absorbs moisture.
Finally the person directing the driver to the weighbridge and weighing - was he an authorised officer?
dvd
cheers dvd.
Yes, although the ramp theory is correct and would explain the discrepancy, the ground was level in this instance so doesn't apply in this case.....any idea what is causing the discrepancy then?
Neither of these defences you mention apply in this case (unfortunately)
And it was a traffic cop that did all the weighing etc - I assume he was an authorised officer??
Yes, although the ramp theory is correct and would explain the discrepancy, the ground was level in this instance so doesn't apply in this case.....any idea what is causing the discrepancy then?
Neither of these defences you mention apply in this case (unfortunately)
And it was a traffic cop that did all the weighing etc - I assume he was an authorised officer??
turbo tim said:Yes.
....any idea what is causing the discrepancy then?
I have been thinking about this.
I know exactly why there is a discrepancy.
When weighing one axle, the fulcrum point is the other axle that is not on the weighbridge.
If you take into account that part of the load which is on the far side of the fulcrum point, (the axle not being weighed) that will act as a counterbalance and will reduce the weight on the axle that is being weighed.
So, if you are weighing the rear axle of the vehicle, the front axle will not be on the weighbridge and that part of the engine which is infront of the front axle will act as a counterweight, making the rear end lighter....
The sum of the weights of each axle ought to amount to LESS than the gross vehicle weight.
Your hypothetical figures posted earlier suggest that the gross vehicle weight is less than the sum of each axle weight. This is not physically possible.
But if the actual weights show the gross vehicle weight to exceed the sum of the axle weights, then there is probably nothing wrong with the weighbridge at all...
Cheers
Pat
No Pat – that seems like complete twaddle to me because the fulcrum effect on the loaded overhangs doesn’t change. So if the vehicle’s total weight is X, this has to be transmitted to the ground to through the two axles as point loads, say X/3 through the front axle and 2X/3 through the rear axle. These loads already incorporate any fulcrum effects.
As the distance between the axles is a constant and the load distribution in the vehicle can be assumed to be constant, every time that the vehicle is stationary and level these loads are transmitted as a vertical reaction into the ground. If one of the axles is on a weighbridge, that doesn’t change anything, still the appropriate proportion of X will be transmitted as a point load.
For me the only explanations are:
a: Operator error in reading or recording the weights.
b: A reading distorting effect in the weighbridge mechanism due to the load not being applied in a distributed manner across the platen, as has already been suggested above. This may be linked to correction factors applied by the operator.
Either way the results as measured seem to indicate that something is wrong with them. The law may be the law but that doesn’t mean that it’s allowed to transcend the laws of physics!
Obviously this is not related to the manufacturer quoted allowable axle loads – these do not have to tally with the overall allowable weight as the allowable axle loads are derived on the basis of structural limitations for the vehicle.
As the distance between the axles is a constant and the load distribution in the vehicle can be assumed to be constant, every time that the vehicle is stationary and level these loads are transmitted as a vertical reaction into the ground. If one of the axles is on a weighbridge, that doesn’t change anything, still the appropriate proportion of X will be transmitted as a point load.
For me the only explanations are:
a: Operator error in reading or recording the weights.
b: A reading distorting effect in the weighbridge mechanism due to the load not being applied in a distributed manner across the platen, as has already been suggested above. This may be linked to correction factors applied by the operator.
Either way the results as measured seem to indicate that something is wrong with them. The law may be the law but that doesn’t mean that it’s allowed to transcend the laws of physics!
Obviously this is not related to the manufacturer quoted allowable axle loads – these do not have to tally with the overall allowable weight as the allowable axle loads are derived on the basis of structural limitations for the vehicle.
Mr E said:
More importantly, why is everyone measuring "weight" (a force) in kilograms (a unit of mass).
You're absolutely correct.......
......but that's what on the form issued by the BiB!!!
The Constabulary's form said:
PLATED WEIGHT (Kg's)
Don't think it's grounds to get the case dismissed though
esselte said:
JUst a question....are weighbridges designed to be used in this way ie 1 axle at a time
Good question......
....I think we've concluded that they obviously don't give accurate results when used in this manner, and that the only accurate way is to weigh all four wheels seperately but simultaneously.
Easy experiment to try at home: get two sets of bathroom scales - put one foot on each and shift your weight between feet - althought the two readings will constantly vary, at any given moment in time, the sum of the two readings will equal your weight.
You can even draw graphs if you like
or you could go for a blatt down your favourite 'B' road - your choice
Question:
Did you breach total load - if so then this discussion, whilst fascinating, is less relevant. The total weight is given, and the only use of the axel weights is to cast doubt on the accuracy of the weighbridge. Will a Magistrate be convinced?.
Did you breach one of the axle weights - if so then there is clear doubt about the methodology and/or equipment. A Magistrate much more likely to be impressed.
Was your excess (whichever of the above)greater than the apparant error - if not then more helpful, if so then less helpful.
Or am I missing something???
Did you breach total load - if so then this discussion, whilst fascinating, is less relevant. The total weight is given, and the only use of the axel weights is to cast doubt on the accuracy of the weighbridge. Will a Magistrate be convinced?.
Did you breach one of the axle weights - if so then there is clear doubt about the methodology and/or equipment. A Magistrate much more likely to be impressed.
Was your excess (whichever of the above)greater than the apparant error - if not then more helpful, if so then less helpful.
Or am I missing something???
Just to add to or possibly resolve, some of the confusion.....
Most folks have seen the picture of the donkey pulling the single axle trailer that is overloaded abaft the wheels that gets sent around on the office e-mails quite regularly? The picture? Donkey is suspended in midair, still in the harness with the rear of the trailer pivoting around the rear axle, touching the ground.
Where is this to the debate in hand, I hear.....
If the load overhang on the rear was a tad less, then the donkey (front axle, perchance?) would be just in contact with the ground but passing minimal weight onto the weighbridge, with the rear of the trailer now clear of the ground. You keeping pace so far?
The individual axle weights need not add together to equal the gross - it all depends on where the load is positioned.
You got a
yet??
Most folks have seen the picture of the donkey pulling the single axle trailer that is overloaded abaft the wheels that gets sent around on the office e-mails quite regularly? The picture? Donkey is suspended in midair, still in the harness with the rear of the trailer pivoting around the rear axle, touching the ground.
Where is this to the debate in hand, I hear.....
If the load overhang on the rear was a tad less, then the donkey (front axle, perchance?) would be just in contact with the ground but passing minimal weight onto the weighbridge, with the rear of the trailer now clear of the ground. You keeping pace so far?
The individual axle weights need not add together to equal the gross - it all depends on where the load is positioned.
You got a
yet?? Eliminator said:
Or am I missing something???
I think you're missing the earlier post from turbo tim which states that his mate is being done for
a) total weight over maximum plated weight
b) front axle ditto
c) rear axle ditto
However we don't know the actual weighings vs the plated numbers. The devil is in the detail on this one I would say.
guizer said:
Where is this to the debate in hand, I hear.....
If the load overhang on the rear was a tad less, then the donkey (front axle, perchance?) would be just in contact with the ground but passing minimal weight onto the weighbridge, with the rear of the trailer now clear of the ground. You keeping pace so far?
The individual axle weights need not add together to equal the gross - it all depends on where the load is positioned.
You got a
Nope, wrong I'm afraid, the total force acted upon the ground by both donkey and cart wheels will still equal the sum of the donkey and cart wheels separately. There is no getting around the laws of physics.
Nel's post is perfectly correct. The results show an inconsistency in the measurement, of that there can be no doubt. The only question is (or should be), does it help the OP's mate?
I'm happy to let all the physics go over my head, but my experiences of weighing vehicles are such that the figures shown do not happen.
All weighbridges I've used show gross vehicle mass as more or less the sum of the individual axle masses plus or minus 20kgs.
If this was not the case, I wouldn't use the evidence.
The only conclusion I can come to is if the ramps to the bridge were down to the bridge or up from the bridge, as the following diagrams indicate.
Clearly an adverse ramp structure could cause a higher weight reading on each individual axle.
Officers should have an 'authority to weigh' which they should show (usually in laminated card form) prior to taking you to a weigh bridge.
All weighbridges I've used show gross vehicle mass as more or less the sum of the individual axle masses plus or minus 20kgs.
If this was not the case, I wouldn't use the evidence.
The only conclusion I can come to is if the ramps to the bridge were down to the bridge or up from the bridge, as the following diagrams indicate.
Clearly an adverse ramp structure could cause a higher weight reading on each individual axle.
Officers should have an 'authority to weigh' which they should show (usually in laminated card form) prior to taking you to a weigh bridge.
nel is bang on the money.
The load on each axle can only change if the load inside the vehicle is moved/changed or there is a change on the fulcum points.
A change in the fulcrum points occurs if the distance between the axels changes - i.e. on of the axels is raised/lowered above the other - thus shortening distance between them.
My money is on Dilberts explanation, the weigh bridge is not capable of accurately weighing a non centred load.
Perhaps a more accurate reading might have been obatained by weighing each axle at the same end of the bridge, ensuring the axle was a far onto the brigde as possible.
Interestingly, if the bridge was deisgned for weighing long load trailers, this anonomoly might have been spotted by moving the van along the bridge, weighing it at three different places. Just on the bridge at one end, centred, and just on the bridge at the other end.
The load on each axle can only change if the load inside the vehicle is moved/changed or there is a change on the fulcum points.
A change in the fulcrum points occurs if the distance between the axels changes - i.e. on of the axels is raised/lowered above the other - thus shortening distance between them.
My money is on Dilberts explanation, the weigh bridge is not capable of accurately weighing a non centred load.
Perhaps a more accurate reading might have been obatained by weighing each axle at the same end of the bridge, ensuring the axle was a far onto the brigde as possible.
Interestingly, if the bridge was deisgned for weighing long load trailers, this anonomoly might have been spotted by moving the van along the bridge, weighing it at three different places. Just on the bridge at one end, centred, and just on the bridge at the other end.
Bit late to the party, but here is my 2p worth......
The weighbridge was probably faulty, not helped by being used incorrectly.
A weighbridge is most accurate when the load is positioned at the centre - hence the gross weight is probably correct.
To weigh the axles singly, the vehicle should be positioned so that the "non weighed" axle is just off the bridge, rather that the "weighed" axle being just on.
TBH the copper had it in for your mate - usually if the whole vehicle is overloaded, that will be the prosecution. Going for all 3 is a bit mean.
What was the max permitted weight of the van?
Steve
The weighbridge was probably faulty, not helped by being used incorrectly.
A weighbridge is most accurate when the load is positioned at the centre - hence the gross weight is probably correct.
To weigh the axles singly, the vehicle should be positioned so that the "non weighed" axle is just off the bridge, rather that the "weighed" axle being just on.
TBH the copper had it in for your mate - usually if the whole vehicle is overloaded, that will be the prosecution. Going for all 3 is a bit mean.
What was the max permitted weight of the van?
Steve
Gassing Station | Speed, Plod & the Law | Top of Page | What's New | My Stuff