Weighbridge accuracy?

Jul 18, 2017
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Is there much point in taking a caravan onto any weighbridge to weigh it to check whether you are within the MTPLM of the caravan? I think the guideline for weighbridges is that they can have up to a 5% tolerance as generally they would be weighing vehicles in the many tons.

If a caravan has an MTPLM of 1800kg if the weighbridge is just within tolerance at 5% this is 90kg either over or under. At 2% tolerance this is still 36kg either way. You could be 50kg over your MTPLM but weigh bridge gives you a reading of 1760kg so you think you are safe.

With us we emptied the caravan completed except for battery which weighed 27kg. The MIRO was supposed to be something like 1690kg. We then weighed everything as we put it into the caravan and weight should have been under 1800kg. We then took it to a weighbridge and it was reading at just under 1900kg. We knew that we had added in less than 100kg taking into account the weight of the battery. No water in caravan and it had blown air heating.

With this in mind although we are confident our current caravan is under the 2000kg MTPLM we have no wish to take it to a weigh bridge that may give us an inaccurate result and resulting in a stressful situation especially if the reading is well over our MTPLM. Not sure how to get around this to get a reading that is within a few kgs i.e. 20kgs.
 
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May 7, 2012
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It is very unlikely that the weighbridge tolerance would be anywhere near 5%. If newly tested it should be very near accurate, so if you are worried you could check with them when it was last tested or the test is due. I appreciate what you say about possible inaccuracies but a weighbridge is the best you can get and you get a ticket showing the results which can be produced if their is a problem later.
You might also look at the weighbridges you have around you. Some take 44 tonne lorries but others only smaller vehicles. The ones that take smaller vehicles are the ones that you will get best results from.
 

JTQ

May 7, 2005
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Possibly the easiest to "lower the unknown" is to take it from one to another weighbridge, or even a trip via three?
If any comes up with a likeable result pay for a ticket from that one, as "proof".

I suspect few will know the accuracy at your weight level, at best their full scale accuracy, anyone know what the authorised tolerance system, for vehicle weighbridges is?

The Reich pads ( 1000 & 1500 kg per wheel versions) come with a plus or minus 3%, so does not greatly alter the precision, and requires careful technique to use with "repeatable" results.
 
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Mar 14, 2005
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As with speeding , weight limits are limits not targets with accepted tolerances there are absolute limits. There is no law that puts tolerances on speed or weight limits.

The tolerances we do see, do not come from the law, but from the organisations that are responsible for monitoring and prosecuting offences. They have to take a pragmatic view based on the practical capabilities and execution of the measurement they use -The need to be confident the margin of error in the measurement is too small to be able to be used as a legal technicality.

There are minimum standards of accuracy required for public weighbridges as described in this document

.

Every weighbridge must have an individual statement that details its limits of resolution and accuracy. For you to be certain you are within your permitted weight limit you must subtract the capability of the weigh bridge form your limit and use that value as your maximum limit figure for this weigh bridge.

This document has some interesting information about alternative weighing systems


but it also includes this :-

The Road Traffic Act of 1988 clearly states it’s the duty of “vehicle users” never to transport an illegal weight.

And this applies to domestic drivers as much as commercial ones.

You should never try to use the uncertainty of measurement as an excuse for overloading.
 
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Jul 18, 2017
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It is very unlikely that the weighbridge tolerance would be anywhere near 5%. If newly tested it should be very near accurate, so if you are worried you could check with them when it was last tested or the test is due. I appreciate what you say about possible inaccuracies but a weighbridge is the best you can get and you get a ticket showing the results which can be produced if their is a problem later.
You might also look at the weighbridges you have around you. Some take 44 tonne lorries but others only smaller vehicles. The ones that take smaller vehicles are the ones that you will get best results from.
Unfortunately there are no weigh bridges for light vehicles near us. There is a weighbridge at the HGV MOT station about 20 miles away.
However the main thrust of my OP was the tolerances allowed on fixed weigh bridge which now appears to be about approximately 20kg.
I would like to also mention that due to misgivings about the accuracy of the weigh bridge we used we bought a Reich weigh scale, but it was a terrible faff to use on a twin axle. Strangely it showed that the caravan was within the 1800kg?
 
May 7, 2012
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I accept that it is not possible to be sure of total accuracy on a weighbridge, but any one used by the police would have the same problem but they will allow at least 5%, so your 2% figure should be safe. They are looking for seriously overloaded vehicles and not minor innocent ones. One solicitor did say to me that he did ask the Police why his clients were always the ones seriously wrong on motoring offences, the answer was they can get all they need where there was no doubt and did not want to get involved off lesser ones.
 
Mar 27, 2011
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Weighing the caravan is very much like home baking, if you make a sponge cake at home you won’t find a label stating any calories so obviously there’s isn’t any, if you don’t weigh the caravan then the weight printed on the plate by the door is obviously spot on, job done.

BP
 
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I accept that it is not possible to be sure of total accuracy on a weighbridge, but any one used by the police would have the same problem but they will allow at least 5%
Every weighbridge that operates in the public sector has to be regularly calibrated and recertified. To be useable it has to operate within the limits tested by Trading standards, but that does not stop it being more accurate than that.

The actual calibrated accuracy should be available to users. There is no legal requirement for the police or any one else to allow 5%. The margin of tolerance will be dependant on the equipment they use. - But its very unlikely they would prosecute for small variations that fall within the

 
Jul 18, 2017
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If we were stopped and found to be over weight for some reason, easy to remove spare wheel and place inside vehicle, That is at least 14kg. I doubt very much if we would be in the naughty zone though as we have roof box and carry odds and ends in it!
 
Jun 16, 2020
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Off topic a bit, sorry, but I took a trailer to a suppliers yard once and they tried to charge me for 1.5 tonnes. I refused to pay as I only had a small trailer which could take 250 kg tops. That logic they refused to accept despite the trailer being in front of them. They tried to take me to court. They totally ignored my explanation, including the weigh ticket not being completed with my car reg. They insisted in trying to prove to me that their weighbridge was recently calibrated at great expense and copied copious amounts of paperwork to me. What had happened is the operator had tried to charge me for someone else’s load.

It did not get to court being thrown out beforehand.

John
 
May 7, 2012
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Weighing the caravan is very much like home baking, if you make a sponge cake at home you won’t find a label stating any calories so obviously there’s isn’t any, if you don’t weigh the caravan then the weight printed on the plate by the door is obviously spot on, job done.

BP
Unfortunately the figure printed on the door may not be accurate as it is the figure produced by weighing one of the original models. As production progresses this can be affected by minor changes in components and bits added to help the production procedure. You will also often find extras added after the sale, movers for example and these can add a serious sum to the unladen weight. A good weighbridge is probably the only accurate way of finding out the true weight of yours.
A wrong weight given by the builder will help in defending an overloading charge, but it will not prevent it.
 

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