Weight differences on ramped weighbridge

[nicholsong]

I expect to find some discrepancy on individual axle weights when the other axle is on the ramped entry/exit to the weighbridge.

Today my axle weights were 1550kg and 2060kg, giving a total of 3610kg.

The vehicle total weight came out as 3800kg, so 190kg difference. Is this the sort of discrepancy one would expect? The ramp for the front axle was about 20 degrees and for the rear about 10 degrees.

The weighbridge is in a builder's yard so may not be calibrated for official weighing.

We had full water and diesel. After we add food and Basia's 60kg we could be just over our 3850kg MPLM , but after 150km(16kg), and a shower each we should be within, even if unlike UK there is not a 5% allowance.

I am not concerned, just interested in the discrepancy. Their old weighbridge was flat.

 

[Jev88]

I have seen an extra weight taken with the other axle on the ramp to compare results.

 

[nicholsong]

I have seen an extra weight taken with the other axle on the ramp to compare results.

Sorry I do not understand that comment, please explain.

 

[Guigsy]

As the centre of gravity is above the axles, when a vehicle points uphill, it'll transfer more weight onto the rear axle. So if the weighbridge has a big step, putting the vehicle at an angle, it will affect the readings.

 

[Vic]

A sloped weighbride would be ok for an indication of gross weight, but useless for accurate individual axle weights. I would find a trading standards approved weighbridge.

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[Mixyblob]

We had our PVC weighed when we first bought it. Front axle first then the whole van. First from second gave the rear weight.
Front and rear were identical. I asked to try it again but they refused.

 

[DBK]

I think the slope will have altered the measured axle weight. If the weighbridge was above the road it will give lower figures. Assuming this was the case when the vehicle was at 20° then you need to add about 6% to the measured reading. For 10° add about 2%. If the smaller reading was your front axle then I get a combined weight of 2744Kg which isn't far off your measured total weight.

If the slope was the other way and the weighbridge was in a dip then you need to subtract the 6% and 2%.

 

[Jev88]

Sorry I do not understand that comment, please explain.

I am assuming you took total weight then drove front axle off weighbridge and weighed again to give indication of rear axle. Reverse rear axle off ramp and take front axle on its own. See if difference is still so large.

 

[nicholsong]

As the centre of gravity is above the axles, when a vehicle points uphill, it'll transfer more weight onto the rear axle. So if the weighbridge has a big step, putting the vehicle at an angle, it will affect the readings.

I thought my expectation of discrepancies showed that I knew this.

 

[nicholsong]

I am assuming you took total weight then drove front axle off weighbridge and weighed again to give indication of rear axle. Reverse rear axle off ramp and take front axle on its own. See if difference is still so large.

I drove on so that front axle was just on plate, then total on, then forward till rear axle was just on edge of plate, which is the standard way to do it I understand.

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[nicholsong]

I think the slope will have altered the measured axle weight. If the weighbridge was above the road it will give lower figures. Assuming this was the case when the vehicle was at 20° then you need to add about 6% to the measured reading. For 10° add about 2%. If the smaller reading was your front axle then I get a combined weight of 2744Kg which isn't far off your measured total weight.

If the slope was the other way and the weighbridge was in a dip then you need to subtract the 6% and 2%.

Many thanks, that was the sort of factoring for the slope that I was looking for. [I assume you meant 3744kg not 2744kg]

Of course the smaller was the front axle as on most MHs.

 

[Guigsy]

Many thanks, that was the sort of factoring for the slope that I was looking for. [I assume you meant 3744kg not 2744kg]

Of course the smaller was the front axle as on most MHs.

10° over a ~4m wheelbase will mean the front wheels are 70cm higher than the back... How big was the step?

 

[SteveRallye]

I get my M/H weighed at local quarry and it is ministry tested approx every 12 months and at its max it can weigh a lorry loaded at 59 tons with a 40 kg discrepancy so pretty accurate. The only thing I find confusing is if she comes in at 3750 all on, the total of the axles when weighed separately added together always seem to come in at approx. 100kgs less adding up to 3650.