Weighbridge (in) accuracies.

[Tommo and Ca]

Decided that a visit to a weighbridge was due. Checked local area and found one in Llanelli. Off we went pretty much fully loaded.
Not going to bore you with the specific weights as not relevant to this thread.
Front axle weighed - whole vehicle weighed - rear axle weighed. Ticket printed. Result showed that we were 240kg overweight !!
I asked the operator about the bridge calibration and all was in order. He looked at the vehicle and said, 'it doesn't look that heavy, let's weigh you again'.
On I went again and this time the overall weight had reduced by 150kg, (now 90kg overweight). Obviously better but still not acceptable. With such a large discrepancy I wondered what I was actually weighing.
As we were traveling to the SW we started looking for a convenient weighbridge en-route to get a 3rd opinion.
One was found in Bath. 140 miles later we arrived and went through the same procedure - front axle, whole vehicle, rear axle.
Despite 140 miles less diesel we now weighed some 260kg overweight. 20kg more than our first weigh.
The specific weights are irrelevant to this story, the point is that in the space of about 3 hours and two (calibrated) weighbridges our total weight varied by about 170kgs (plus about 20 litres of fuel) which equals approx 190kgs variance.
Having seen many members quoting their overall weights as being close to their plated weights, how many are actually overweight? How much reliance can we motorhomers place on these weighbridges?

 

[Speve]

Not a lot by the sound of it?

 

[Sandancers]

The calibration of the weighbridge should be easily traced, see if they have a website and look on there. You'd also have to bear in mind that the weighbridge could be a max weight of say 60T which means on a 3.5T MH the % error could be in the region you quote yet still be in calibration.

 

[Tommo and Ca]

The calibration of the weighbridge should be easily traced, see if they have a website and look on there. You'd also have to bear in mind that the weighbridge could be a max weight of say 60T which means on a 3.5T MH the % error could be in the region you quote yet still be in calibration.

Calibration was checked and was fine. But you raise a very good point about % errors. How many M/H's are aware of this and how much of an effect this could have if stopped.

 

[Sandancers]

The calibration cert should tell you the max weight of the weighbridge and the % error allowed. Therefore if the bridge had a range of 0 - 100T and a 1% allowable error then 1T out would still pass the calibration. Bear in mind that it is most likely to be reading in-correctly at the lower end of the scale also.

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[funflair]

The calibration cert should tell you the max weight of the weighbridge and the % error allowed. Therefore if the bridge had a range of 0 - 100T and a 1% allowable error then 1T out would still pass the calibration. Bear in mind that it is most likely to be reading in-correctly at the lower end of the scale also.

Would it? surely the % tolerance should be linear through the range of the bridge.

Martin

 

[Sandancers]

Would it? surely the % tolerance should be linear through the range of the bridge.

Martin

Theoretically yes, but the effects of stiction and the way the load cells operate mean it is most accurate from about 1/8 scale upwards.

 

[TinaLes]

Thats not very reassuring for us MH owners, we need more accuracy at smaller weights as we are not 44 ton lorries.
It might be worth investing in buying our own scales, from memory I think they are available from Reich, but my search just now failed to show the ones I have seen other funsters use in the past.
They were used at a Fun Rally a few years back, and most funsters being "fully loaded" for the meet, were indeed overweight!. (I am talking about the vans of course, not the funsters)
The idea is that you drive each wheel up on the weighing bar/pad, it then tells you the individual weights for each wheel/axle and the the overall weight.
Hopefully someone will come along soon and tell us which scale type & price that I cannot seem to find today.
Weighbridges are as rare a rockin horse stuff round here in Surrey.
LES

 

[Brains]

Personally I find that very disturbing.

Given how easy it is to define accuracy on a weigh bridge (a 1m X 1m X 1m cube of water weighs 1,000kg) you would have thought that even a 1% range of error (10kg per tonne) could be fine tuned out.

A 1% discrepancy would mean a 40T lorry could load an extra half tonne

The percentage variation you give would equate to about a 6% variation (Approx 60kg per tonne)
Which would mean a fully loaded lorry could have a fully loaded motorhome craned on the roof and still be underweight!

 

[RandallC]

Could be an S shaped curve. You just dont know unless you see a graph of the readings when weighing the calibration weights.

Generally all calibration data is + or - X% sometimes for specific conditions it's stated which direction the error is in.

Talking general calibration not necesarily specific to weighbridges. Didn't run the contract for ours so have a bit of a gap there.

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[Kannon Fodda]

Weighbridges are as rare a rockin horse stuff round here in Surrey.

There is one at J9 M25, Leatherhead. Top Tip: It's not open to the public, and you don't want to be directed to use it. If you are overweight you won't be leaving until you've reduced the weight and you'll have a nice fine to pay too.

 

[Sandancers]

Personally I find that very disturbing.

Given how easy it is to define accuracy on a weigh bridge (a 1m X 1m X 1m cube of water weighs 1,000kg) you would have thought that even a 1% range of error (10kg per tonne) could be fine tuned out.

A 1% discrepancy would mean a 40T lorry could load an extra half tonne

The percentage variation you give would equate to about a 6% variation (Approx 60kg per tonne)
Which would mean a fully loaded lorry could have a fully loaded motorhome craned on the roof and still be underweight!

I have no idea what the accuracy of a weighbridge is, it could be 0.01 percent, I just used 1 percent as an example.

If you have a 3.5T MH then you really want to be weighing it on a 5T range weighbridge, that would certainly give you accurate figures.

 

[Dorset Diver]

Did you factor in the Breakfast - Number twos + Double burger, fries, and donuts. Also was the OH on and then off and then on the van again? Just asking .

The weighbridge I use is very accurate. Went there one day with SWMBO who's weight I know. With her on board the figure was exactly up on what it was without her in the cab.

If you have doubts best to use a local council WB they are carefully checked and calibrated.

 

[mpdcymru]

The Consolidated Code of Practice for the Enforcement Weighing of Vehicles says that a static or "plate" weighbridge must have an accuracy of 50 kgs per axle and says that for "dynamic" weighbridges the accuracy limit should be 150 kgs per axle and the concequent gross or train weight should be subjet to a variation of + or - 150kgs multiplied by the number of axles on the vehicle or vehicle combination, The COP doess allow for the inspector of the weighbridge to allocate a different limit iof accuracy if s/he sees fit.

In enforcement weighings DVSA used to allow 5% or a tonne on axle. gross and train weight before giving a graduated fixed penalty or considering prosecution - this may have changed.

 

[grumfy]

Thats not very reassuring for us MH owners, we need more accuracy at smaller weights as we are not 44 ton lorries.
It might be worth investing in buying our own scales, from memory I think they are available from Reich, but my search just now failed to show the ones I have seen other funsters use in the past.
They were used at a Fun Rally a few years back, and most funsters being "fully loaded" for the meet, were indeed overweight!. (I am talking about the vans of course, not the funsters)
The idea is that you drive each wheel up on the weighing bar/pad, it then tells you the individual weights for each wheel/axle and the the overall weight.
Hopefully someone will come along soon and tell us which scale type & price that I cannot seem to find today.
Weighbridges are as rare a rockin horse stuff round here in Surrey.
LES

I have one of those “Caravan Weight Control” devices from Reich with a max load of 1500 kg so upto 6 tonne for 4 wheels. Bought some 5 or 6 years ago and not used since as moved onto twin rear wheels and it could not cope with them. It was difficult to use as you needed a level stretch of road and it required you to drive over it slowly but not too slowly and not too fast or it would show up a fail symbol of a hare! It needs two of you to do it really, one outside shouting “hare” each time you failed. My wife refused to continue helping after the first dozen or so fails. Comformatic box not amenable to delicate control at very low speeds.
Still look to be on sale for around £180 and slightly cheaper for 1000 kg version.

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[Lenny HB]

Weighbridges are calibrated at 17-18 tonnes they are designed to weigh 44 tonne lorries.
If you look at the gov website on Weighbridge calibration the limits are for a plate Weighbridge +/- 100kg and a dynamic Weighbridge +/- 150kg per axle.

I use to use a local dynamic weighbridge depending on speed and line up I can get differences of 30-50kg. I take 3 or 4 readings and take the average.

In practice with modern strain guages they are far more accurate.

 

[chaser]

This is the one I have, and have found it very accurate, even weighed a small lorry with it, although it wasn't anywhere near this dear.

 

[namwaldog]

This rather 'heavy' reading explains tolerances on weighbridge...

Consolidated code of practice: enforcement weighing of vehicles

www.gov.uk

It may be that these inconsistencies in weighbridge recordings result in this guidance from VOSA.....

3.6 Excess Weight Offences
When a fixed penalty notice or conditional offer is issued for an excess weight offence, the examiner will also prohibit the driving of the vehicle on a road. The prohibition is designed to stop an overweight vehicle from being used on the road and to preserve road safety.
The fixed penalty will be the preferred option for dealing with excess weight offences, unless the offence is too serious to warrant the issue of a fixed penalty or the maximum number of notices (as explained in section 3. 2) would otherwise be exceeded. Below is a
table showing the current graduated penalty levels for excess weight matters:
EXCEED WEIGHT
Severity Endorsable FP amount
0 up to but not including 10% No £60.00
10% up to but not including 15% No £120.00
15% and over No £200.00
The legislation shows that a £60.00 penalty will be levied for a 0%-9.99% overload, but VOSA examiners will allow a 5% tolerance before Fixed Penalty or Prohibition issue
unless the relevant weight has been exceeded by 1 tonne or more. It is likely that a fixed penalty would be inappropriate for serious cases of overloading (i.e. in which the vehicle is overloaded by 30% and over, or the excess weight is 5 tonnes or more) and therefore a
court summons would be issued.
If the effect of the excess weight and the manner in which the load is carried is having a significant effect on road safety, for example causing serious instability or loss of directional control, alternative construction and use or road traffic offences that will need to go to court may be appropriate, with the excess weight contributing to the offence.


This 5% tolerance on a 3500kg MH works out at 175kg

Barry

 

[SpeedyDux]

If a dynamic weighbridge has a tolerance of 150 kg per axle that doesn't necessarily mean it should average out. My take is that's up to 300 kg under/over in total for a 2 axle 3500 kg MTPLM Van. Such a van might give a false reading of 3800 kg despite not being overweight. Does that mean VOSA examiners will treat it as showing excess weight of 125 kg and issue a £60 penalty? In a marginal set of circumstances this has potential for injustice. Stay lucky and don't get pulled over on suspicion of excess weight.

 

[Lenny HB]

If a dynamic weighbridge has a tolerance of 150 kg per axle that doesn't necessarily mean it should average out. My take is that's up to 300 kg under/over in total for a 2 axle 3500 kg MTPLM Van. Such a van might give a false reading of 3800 kg despite not being overweight. Does that mean VOSA examiners will treat it as showing excess weight of 125 kg and issue a £60 penalty? In a marginal set of circumstances this has potential for injustice. Stay lucky and don't get pulled over on suspicion of excess weight.

Just play safe and make sure you have 300kg spare cover all variations, that's what I do

100kg on a 44 tonner is only 0.23% it does seem daft weighing 3.5 t vehicle on the same scales but in practice they are probably not going to be more than 50kg out worse case.

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[BusyBuilder]

WE had ours weighed and carry the certificate, if we did get stopped we would show the cert, not sure if it would have any sway, but having a cert must help ?

 

[Lenny HB]

WE had ours weighed and carry the certificate, if we did get stopped we would show the cert, not sure if it would have any sway, but having a cert must help ?

I can't see them taking any notice of it unless it was ten minutes before you were stopped.

 

[mpdcymru]

WE had ours weighed and carry the certificate, if we did get stopped we would show the cert, not sure if it would have any sway, but having a cert must help ?

A certificate of weight is only valid for the single journey during which it was given to the driver. Clearly it cannot be evidence of weight if it was issued several dyas ago as much could have changed in the vehicles load since then, An enforcement officer may take it as evidence that the driver is at least aware of the issue - how this would affect his/her decision on the day is unknown.

 

[Kannon Fodda]

Enforcement chap is more likely to take a previous cert that you know you have to comply so why didn't you this time. If previously you had plenty of headroom, why have you crammed so much on you are now negligent by being overweight. If you knew before you were close to the limit then again why weren't you being careful not to put more weight on board. I'd be hiding that certificate before it contributes to your demise.

 

[GWAYGWAY]

Drive enthusiastically onto the weighbridge and shake it a bit, lorries are more able go get it working gently as they are 10 times your weight. The stiction for you is higher.
my first weighing showed the van at 4200kgs empty and it was meant to be 3500kgs, the front wheels just on and rear wheel just on and I was lifting the weighbridge like a see saw the next time at another site I drove on so the rear wheels were just off and the same at the other end front wheel just off and the weight was 3200kgs empty. The first one panicked me as the £80000 van was heavy and empty. I though tI was done for. It did uprated to 4200kgs for a huge carrying capacity before the accessories were fitted.

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[SteveRallye]

Had my M/H uprated to 4000kg from 3800 as I was just overweight. a paper excercise with SVTEC as I had already had air susension fitted at same time as the towbar,this was due to the fact that a lot of M/H are now coming with long overhang as mine did. When I visited the local Quarry weighbridge the weights and measures were there with an artic loaded with massive weights and a forktruck placing them on. They asked me to come back in 30 minutes which I did . The owner operator said they were tested every 12 mths at this time of year and they were accurate to within 40 kg. So I felt quite happy with the outcome.

 

[Rapido925M]

I always check the readings from the rolling road brake test as part of the MOT.
I write it in my MHF Yearbook and accept it as reasonably accurate, giving guidance for how much I can add

Gordon

 

[poppycamper]

WE had ours weighed and carry the certificate, if we did get stopped we would show the cert, not sure if it would have any sway, but having a cert must help ?

G

WE had ours weighed and carry the certificate, if we did get stopped we would show the cert, not sure if it would have any sway, but having a cert must help ?

WE had ours weighed and carry the certificate, if we did get stopped we would show the cert, not sure if it would have any sway, but having a cert must help ?

But listening to comments on here how do you know the certificate you religiously carry around with you is accurate.
Pretty sure if stopped and weighed the authorities would go by what their scales say and not what a certificate you have that could be from anywhere!!!

 

[poppycamper]

I have one of those “Caravan Weight Control” devices from Reich with a max load of 1500 kg so upto 6 tonne for 4 wheels. Bought some 5 or 6 years ago and not used since as moved onto twin rear wheels and it could not cope with them. It was difficult to use as you needed a level stretch of road and it required you to drive over it slowly but not too slowly and not too fast or it would show up a fail symbol of a hare! It needs two of you to do it really, one outside shouting “hare” each time you failed. My wife refused to continue helping after the first dozen or so fails. Comformatic box not amenable to delicate control at very low speeds.
Still look to be on sale for around £180 and slightly cheaper for 1000 kg version.

Interesting comment.. I presume when you say twin rear wheel you mean dual wheels and not tag axle.. I ask because I thought about one of these but could not decide if it would take my dual rear wheels... So by what you say it won't.. thanks.

 

[PeteH]

Weighbridge scales, are prime examples of heavy engineering structures subjected to much abuse, and whilst a good guide to the loaded condition of any vehicle using them. Their accuracy on any given day can and will IMV vary?. i.e. Hot day?, Cold Day? We have one locally, more than capable of weighing tri-axle LGV`s, at the farm behind where I built my House in the 90`s. I still go and periodically run the `Van over it just to check that SWMBO is not sneaking more "crap" into the lockers and throwing my beer out!. All joking apart the last 3 "tickets" (Matthew, just gives me the weights, not an official document) have had discrepancies due to fuel mostly I would think, but have been within a reasonable ball park IMV. My understanding BTW is that a 5% tolerance is accepted by VOSA (or whatever they are called this week?). Which on my GVW would be just short of 200kg.

I considered the purchase of a Reich type Device, and I suppose like all similar devices whilst it`s accuracy under non ideal condition might be "iffy", it could conceivably form the basis of (legal) dispute if the "ministry" device showed excess?. (Obviously on the same day and same time-frame)

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