WEIGHBRIDGE CELIBRATION

[Brian Kirby]

Now you're at it as well, Mel!!  Some silly sod at VOSA dreadfully confused poor Bas, and I explained it as clearly, and gently, as I could.  The simple answer, as Clive says, is that all the rest is codswallop, including, I regret to say, your contribution above.  :-)

I'll try again.  If the approach to a weighbridge, or the departure from it, is not level, then the vehicle (especially a short wheelbase vehicle) will change angle as it arrives, or leaves.  To weigh just the front axle, the rear axle must be off the weighbridge.  If the rear axle is not then at the same level as the front, due to the aforementioned incline, there will be some small shift in the centre of gravity of the van, and that will affect the load registered on the weighbridge.  In practise, that shift will be very small, and probably below the sensitivity of the weighbridge to register, since most only record 10Kg increments.  Nevertheless, it will be there.  Now, if the vehicle is driven fully onto the weighbridge any loss (or gain) at therear will be recovered, and the ALW will be correctly recorded, although the front axle load may have been slightly under, or over, recorded.  Rear axle load will then be ALW minus (under, over, or correctly) recorded front axle load.  This is the safe, safe cancelling, foolproof method.

If, however, in order to record the rear axle load, the van is then driven forward so that the front axle is now off the other end of the weighbridge, and so possibly on another incline, the inaccuracy will be repeated and the rear axle load will become distorted.  Again, it is extremely unlikely the inaccuracy would be within the range of sensitivity of a weighbridge designed to weigh vehicles up to 40+ tonnes!  However, if this method is employed, unless both approach and exit are dead level, this is what will happen.  So, in the worst case, at a guess, if both axles slightly under (or over) record due to incline, there could be a discrepancy in ALW, compared to what would be obtained by standing the van level with all four wheels centred on the platform.  Moral, weigh one axle, then the whole van, and get the second axle load by deducting 'tother from which.

All this stuff about bikes and moments is completely irrelevant to weighing the vehicle: it is only relevant to calculating the additional load a bike (or scooter) would impart to the rear axle of a van.  Even then, the corresponding load subtracts from that on the front axle, since the weight of the whole must be equal to the sum of the weights of its parts.

So, to (over) quote Clive, all else is total and unmitigated codswallop!  :-D

[Mel B]

Calm down Brian ... you've pretty much said what I've said, but just used a load more words! I'm on word rationing ... :D (lol)

[Tony Jones]

Just a small cat among the pigeons:

Clive, in your OP you said part of your van's diet involved building a trailer for the bikes: is your GTW (Gross Train Weight) still OK?

[Mel B]

Tony ... that was Clive's previous motorhome (Autotrail), he's now got his gin palace (Concorde) with tonnes of payload to spare ... nearly enough to stick a coachbuilt motorhome on top ... or your van!!!! :D

[Harvey]

Clive - 2010-04-14 4:10 PM

 

Well this afternoon with everything loaded, that both motorbikes in the garage, two complete commercial gazebos, full water tank etc, oh and the Mrs, we still have 180 KG spare capacity overall and both axles are well within ratings!!

 

 

Having read all the following posts ...... :'( .... I have just one important question.

 

Where, near Basingstoke, did you find a weighbridge Clive?

 

Harvey

[lennyhb]

Doesn't matter which way you look at it at the end of the day if you get stopped at a roadside check they will check the axle weights & if you are over your nicked.

 

 

[Homenaway]

Hi,

 

Just taken our Adria Twin to our local weighbridge and although not in full touring trim but both of us in it and the water tank empty we have 240Kg to spare :-D

 

They weighed the front axle 1620Kg (1750 max) and total weight 3060Kg (3300 MGW) giving 1440Kg (1900 max) on the rear axle.

 

Any weighing device is going to have a minimum weighing threshhold and and resolution eg 20 or 40Kg interval as well as a permissible error against a reference standard.

 

Now just got to workout the best tyre pressures for these weights!

 

Steve

 

 

[Tony Jones]

We visited one near us for the first time on our way out to Plymouth on Friday. Never bothered before as I've always assumed there wasn't room in a panel van to overload it, but thought I'd check - especially as we're taking two passengers to Warwick in the summer for a church camp, while towing someone else's caravan!

 

Anyway, our max is 2800kg and we came in at 2720 with just the two of us, but with a full (70ltr) water tank. So since our proposed passengers aren't big people, travelling with an empty tank should see us right. But I was surprised how close it was. Incidentally, the axles were exactly even at 1360 each - both well within limits.

 

Now comes the tricky bit - caravans are a closed book to me. My "Gross Train" figure is 3500kg, so assuming I'm running close to the van limit I'll only have 700kg to tow. Is that realistic for a (rather old and basic) caravan? Do they have a weight-plate on them, to which you can add any extras inside, or do you just have to trundle off to the weighbridge with the whole caboodle?

[Brian Kirby]

It will have a plate, Tony (probably on the side of the A frame) which, unless it is very old, will give the MAM and the max permissible axle load.  Nothing will tell you its unladen weight.  As you have said it is old, it is likely to be quite heavy, and the best clue to unladen weight will be MAM.  Caravans generally do not have very high payloads but, as with your van, the only way to know for sure is a weighbridge.  However, 700Kg laden would be a very light caravan, so if much larger than 3 berth I think you may struggle.  (Even those dinky little Eriba Puck vans are 700Kg MAM - they were originally 500Kg, but with virtually zero payload!)  Old vans tend to have old tyres, and caravan tyres work surprisingly hard.  Look hard at them and treat with great suspicion if over 7 years old.  Would be wise to check spare situation as well.

Final thought.  You need to get about 7% of the actual laden weight of the van as downforce on the towball.  Much less, and you risk the caravan becoming unsteady, especially if windy, or downhill.  A 700Kg laden caravan will therefore put another 50Kg onto the actual laden weight of your van!  Unless you can lighten your van, or can travel with the caravan unladen, therefore, I think you're going to have to do some ingenious juggling, and that you'll need a weighbridge to hand while you do it!  Maybe fill the caravan with helium balloons?  :-D 

[Tony Jones]

Thanks Brian, this is what I was afraid of.

 

Last time we went to the same event, I towed a borrowed trailer, which carried various people's camping gear (since we'd filled all available cars with people!).

One of those (former) camping families now has this old caravan (but as yet no towcar), and others are looking greedily at the space inside it with a view to getting their tents etc transported. That, it seems, just ain't gonna happen, even if I can take the caravan!

We've got a few spare seats in cars this year, so maybe we'll need to get one of the car drivers to take a hired van instead, and lighten everyone's load - mine included!

 

Any other comments from anyone?

[Clive]

Tony,

Small old caravans were not light. If you want a light weight caravan then it needs to be NEW and small. The old Sprite Alpine for example was a heavy old beast.

C.

 

[Harvey]

Clive,

 

Would you answer this please ........

 

"Where, near Basingstoke, did you find a weighbridge Clive?"

 

Ah! I have found GB Foot. Did you use them or somewhere more convenient?

 

Thanks in adavance

 

Harvey