HymerVan Posted April 27, 2017 Share Posted April 27, 2017 i recently went to a local (very helpful) private weigh-bridge to weight my new van in "touring condition". No unpleasant shocks and plenty residual payload I put whole van on weigh-bridge then reversed off partially leaving the front axle on the weigh-bridge. This gave me two weights :- Whole vehicle Front axle The rear axle load can be calculated (by subtraction). Actually the load on each axle is close to being the same. However I am now questioning this methodology because my knowledge of "O' Level physics (levers) is long forgotten. Does it make a difference how much of the van is on the weigh-bridge so long as one axle is on and one off ? If the answer is yes how do you position the vehicle ? My van has almost a wheel at each corner but others will not be so symmetrical and may have a long overhang behind the rear axle. Link to comment Share on other sites More sharing options...
Agaric Posted April 27, 2017 Share Posted April 27, 2017 Must pay more attention in class, write this out 50 times and see me after. The method on the weighbridge was correct. Link to comment Share on other sites More sharing options...
crocs Posted April 27, 2017 Share Posted April 27, 2017 That's the way (see what I did there? *-) ) I've always done it. Link to comment Share on other sites More sharing options...
Barryd999 Posted April 27, 2017 Share Posted April 27, 2017 When I have weighed mine I have done the whole van then the van half off forward and half off back for the rear and front axles. The weights on the print out of each axle added up to the weight for the full van so I guess it works. I was approximately half off for each axle. Link to comment Share on other sites More sharing options...
colin Posted April 27, 2017 Share Posted April 27, 2017 The only time it would make a difference is if it had a slope on/off, and even then it would have to be quite a slope to make an appreciable difference. Link to comment Share on other sites More sharing options...
ron. Posted April 27, 2017 Share Posted April 27, 2017 I did read somewhere that for optimum weighbridge accuracy you should position your vehicle, or individual axle, as near to the centre of the plate as possible - not the edge. Link to comment Share on other sites More sharing options...
Robbo Posted April 27, 2017 Share Posted April 27, 2017 I visited a weighbridge with a fairly significant ramp both ends. Whole vehicle weight 3880Kg. Weighed both axles individually and when added together it gave 3860Kg. So, only 20Kg between individual axle weights and whole. However, the weighbridge only seemed to measure to the nearest 20Kg anyway. Probably best, when weighing individual axles, is to get the axle being weighed as far on the weighbridge as possible. My reasoning for this is, that the weighbridge will probably give more accurate readings when loaded as close as possible to the midway point. Link to comment Share on other sites More sharing options...
plwsm2000 Posted April 27, 2017 Share Posted April 27, 2017 Laurence, Just to add that when you subtract the two readings, the result could give double the measurement error. To attempt to explain, lets say your true weights were 1499kg on the front and 1501kg on the rear (3000kg total). If the weighbridge accuracy/resolution is 20kg, the total reading could be 3020kg which is still be within its accuracy specification. If you then weighed the front, it could read 1480kg (still within the 20kg error spec.). When you do the subtraction 3020-1480, the rear would appear to be 1540kg (not 1501kg). Obviously this is the worst case condition, but could occur. My suggestion is that if you know you are quite close to the limit on one axle, always measure that axle rather than calculate it from the total. As others have said, it is quite important that the van is at the same level each time you take a reading. If not, the loads will transfer onto the other axle and depending on the vans centre of gravity, you could get a noticable error (fuel, water and any other liquids will also move around a bit). I am usually closer to the front axle limit than the rear so this is what I normally do (if I am allowed to!). 1) Drive forward and get the OH to signal me to stop when the rear wheels are just a few inches from the weighbridge (i.e still on firm ground). If there is a bit of a ramp onto the weighbridge, then I try to stop as close to the top of the ramp as possible (this is where you need some cooperation from the OH) 2) Switch off the engine and with the OH back in the passenger seat, signal to the weighbridge operator to take a reading (front axle weight) 3) Drive forward roughly about half the length of the vans wheel base. There are two reasons why I do this - a) the total van load is roughly spread around the same point as the front axles were measured (my van is usually about the same weight front-rear) and b) it prevents lorry drivers with some sort of grudge against motorhomers from driving onto the weighbridge behind you! (from personal experience :-( ) 4) Switch off engine and signal to operator to take the second reading (total weight) 5) Subtract front from total weight to get rear weight. Step 3 is not critical and you should be ok as long as all your wheels are a reasonable distance (>1mtr?) from the edge of the weighbridge. Phil Link to comment Share on other sites More sharing options...
crocs Posted April 27, 2017 Share Posted April 27, 2017 Why switch the engine off? Link to comment Share on other sites More sharing options...
plwsm2000 Posted April 27, 2017 Share Posted April 27, 2017 crocs - 2017-04-27 9:32 PM Why switch the engine off? Just being pedantic - it is to stop any vibration affecting the measurement. Weighbridges don't measure mass directly - they measure the force due to the object (in Newtons) and then calculate the mass (in kg) using Force = mass * acceleration (Newtons second law of motion). Acceleration being due to earth's gravity but any vibration will add to this. As I say, just being pedantic - I cannot say if the engine running would cause a measurable error, but it easy to switch off. Link to comment Share on other sites More sharing options...
keninpalamos Posted April 28, 2017 Share Posted April 28, 2017 Barryd999 - 2017-04-27 1:00 PM When I have weighed mine I have done the whole van then the van half off forward and half off back for the rear and front axles. The weights on the print out of each axle added up to the weight for the full van so I guess it works. I was approximately half off for each axle. when weighing an individual axle it won't make any difference where it is on the weight bridge as the axle weighs what it weighs. It's like saying if I pick it up over there will it be lighter than here, which put like that sounds very silly. As long as the vehicle is level and not moving and the weigh bridge is reasonably accurate. Link to comment Share on other sites More sharing options...
keninpalamos Posted April 28, 2017 Share Posted April 28, 2017 plwsm2000 - 2017-04-27 10:05 PM crocs - 2017-04-27 9:32 PM Why switch the engine off? Just being pedantic - it is to stop any vibration affecting the measurement. Weighbridges don't measure mass directly - they measure the force due to the object (in Newtons) and then calculate the mass (in kg) using Force = mass * acceleration (Newtons second law of motion). Acceleration being due to earth's gravity but any vibration will add to this. As I say, just being pedantic - I cannot say if the engine running would cause a measurable error, but it easy to switch off. excellent! Couldn't have put it better myself....what about an earth quake? :D Link to comment Share on other sites More sharing options...
crocs Posted April 28, 2017 Share Posted April 28, 2017 plwsm2000 - 2017-04-27 10:05 PM crocs - 2017-04-27 9:32 PM Why switch the engine off? Just being pedantic - it is to stop any vibration affecting the measurement. Weighbridges don't measure mass directly - they measure the force due to the object (in Newtons) and then calculate the mass (in kg) using Force = mass * acceleration (Newtons second law of motion). Acceleration being due to earth's gravity but any vibration will add to this. As I say, just being pedantic - I cannot say if the engine running would cause a measurable error, but it easy to switch off. Great explanation. And while there's no harm in being a pedant, you can get treatment. :-D Link to comment Share on other sites More sharing options...
HymerVan Posted April 30, 2017 Author Share Posted April 30, 2017 Thanks everybody for your helpful contributions. The actual weights recommended by Conti (who incidently replied with lightning speed and in a most detailed manner) are FR 48 and rear 51 Link to comment Share on other sites More sharing options...
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