I have free access to a weighbridge. I want to check my overall caravan weight and the towball weight when it's fully loaded. How do you check your towball weight? Do you:
1. Check the weight of just the car when the caravan is connected and then the weight of the car when the caravan is disconnected and subtract the two values or
2. Somehow support only the towball cap of the caravan on the weighbridge or
3. Something else?
yobarr said
07:35 PM Jun 28, 2021
Buzz Lightbulb wrote:
I have free access to a weighbridge. I want to check my overall caravan weight and the towball weight when it's fully loaded. How do you check your towball weight? Do you:
1. Check the weight of just the car when the caravan is connected and then the weight of the car when the caravan is disconnected and subtract the two values or
2. Somehow support only the towball cap of the caravan on the weighbridge or
3. Something else?
Easy way is weigh van with van wheels and jockey wheel both on weighbridge,then reconnect van to car and take weight on van wheels away from total weight.This is a VERY inaccurate way to do things,as weighbridges generally weigh in 20kg increments,but it will give you a rough idea.Towball weight is generally accepted as being 10% of total van weight.There are other,far more accurate,ways to measure towball weight,however.Cheers
Rob Driver said
10:12 AM Jun 29, 2021
Buzz,
Yobarrs method is probably the most simple way to get a close approximation.
Most weigh bridges these days use electronic load cells and there can be a discrepancy between the cells.
You are lucky to have free access to the bridge and you might want to weigh as per yobarrs suggestion and then turn your rig around on the weigh bridge and weigh it the same way but approaching from the other direction.
You may or may not get differing weights but if you do you might take the average of the difference and factor that by adding or subtracting the difference.
By general operations of most weigh bridges the load is always weighed in the same direction and as such the mechanics of that repeated action may affect the result.
The important thing is to weigh anything on a weighbridge positioned as central to the plate as possible. In other words a drawbar jockey when on one end of a plate will in most cases be inaccurate.
There are companies with mobile load cells that will weigh your van accurately but their services are not free.
Another option is watch forums and local news pages when it may happen that authorities will set up a weighing station in you area just to help caravaners achieve correct weights.
On a side note..
Many years ago I drove a truck that had load cells fitted to the prime mover and the trailer and I attracted the interest of authorities in a country town whereby they insisted that they weigh me so as to prove the accuracy of the weighing system in the truck.
They took me to a local weigh bridge and weighed me and I was half a tonne over which meant I was overweight and illegal.
I cant believe my luck that day when the senior of the two officers suggested for the exercise that I turn the rig around and weigh from the other direction and at least to my surprise the truck was now legal.
This was also a problem with the Highways Dept weigh bridge on the Dukes Highway at Keith is SA. They weighed trucks from both directions but generally favoured westbound trucks and that bridge was reported to weigh differently depending on the direction of approach.
Buzz, for general purposes the suggested method will be fine because wherever you weigh there will, at most times, be a discrepancy.
And in any case you will be a hell of a lot closer than the person who blindly assumes his weights are correct.
Regards
Rob
iana said
11:05 AM Jun 29, 2021
If you weigh the tow ball using the above method, you must make sure the caravan is at the same angle longitudinally as it was when hitched to the vehicle. Any change of angle will move the center of gravity of the van (trailer) forward or back and the tow ball weight will not be true.
Rob Driver said
11:40 AM Jun 29, 2021
iana wrote:
If you weigh the tow ball using the above method, you must make sure the caravan is at the same angle longitudinally as it was when hitched to the vehicle. Any change of angle will move the center of gravity of the van (trailer) forward or back and the tow ball weight will not be true.
A good point Iana,
The simple way is to count the number of turns of the handle on the jockey wheel to just clear the tow ball or pin then wind the leg back down that same number of turns with the vehicle removed.
Regards
Rob
yobarr said
01:03 PM Jun 29, 2021
iana wrote:
If you weigh the tow ball using the above method, you must make sure the caravan is at the same angle longitudinally as it was when hitched to the vehicle. Any change of angle will move the center of gravity of the van (trailer) forward or back and the tow ball weight will not be true.
Ensuring the same longitudinal angle is especially important if the van does not have load sharing suspension,as any drop in drawbar height will reduce weight on towball,while raising the drawbar increase weight on towball.The change in towball weight with load sharing suspension is to little that is very difficult to even measure.Cheers
Gundog said
03:30 PM Jul 12, 2021
Its not an overly important number towball weight, too much time is spent discussing a weight that is only applicable before connecting to the tow vehicle.
The theroetical towball weight changes with the Yaw, Pitch and Roll of the moving combination, along with the terrain.
I have free access to a weighbridge. I want to check my overall caravan weight and the towball weight when it's fully loaded. How do you check your towball weight? Do you:
1. Check the weight of just the car when the caravan is connected and then the weight of the car when the caravan is disconnected and subtract the two values or
2. Somehow support only the towball cap of the caravan on the weighbridge or
3. Something else?
Easy way is weigh van with van wheels and jockey wheel both on weighbridge,then reconnect van to car and take weight on van wheels away from total weight.This is a VERY inaccurate way to do things,as weighbridges generally weigh in 20kg increments,but it will give you a rough idea.Towball weight is generally accepted as being 10% of total van weight.There are other,far more accurate,ways to measure towball weight,however.Cheers
Yobarrs method is probably the most simple way to get a close approximation.
Most weigh bridges these days use electronic load cells and there can be a discrepancy between the cells.
You are lucky to have free access to the bridge and you might want to weigh as per yobarrs suggestion and then turn your rig around on the weigh bridge and weigh it the same way but approaching from the other direction.
You may or may not get differing weights but if you do you might take the average of the difference and factor that by adding or subtracting the difference.
By general operations of most weigh bridges the load is always weighed in the same direction and as such the mechanics of that repeated action may affect the result.
The important thing is to weigh anything on a weighbridge positioned as central to the plate as possible. In other words a drawbar jockey when on one end of a plate will in most cases be inaccurate.
There are companies with mobile load cells that will weigh your van accurately but their services are not free.
Another option is watch forums and local news pages when it may happen that authorities will set up a weighing station in you area just to help caravaners achieve correct weights.
On a side note..
Many years ago I drove a truck that had load cells fitted to the prime mover and the trailer and I attracted the interest of authorities in a country town whereby they insisted that they weigh me so as to prove the accuracy of the weighing system in the truck.
They took me to a local weigh bridge and weighed me and I was half a tonne over which meant I was overweight and illegal.
I cant believe my luck that day when the senior of the two officers suggested for the exercise that I turn the rig around and weigh from the other direction and at least to my surprise the truck was now legal.
This was also a problem with the Highways Dept weigh bridge on the Dukes Highway at Keith is SA. They weighed trucks from both directions but generally favoured westbound trucks and that bridge was reported to weigh differently depending on the direction of approach.
Buzz, for general purposes the suggested method will be fine because wherever you weigh there will, at most times, be a discrepancy.
And in any case you will be a hell of a lot closer than the person who blindly assumes his weights are correct.
Regards
Rob
A good point Iana,
The simple way is to count the number of turns of the handle on the jockey wheel to just clear the tow ball or pin then wind the leg back down that same number of turns with the vehicle removed.
Regards
Rob
Ensuring the same longitudinal angle is especially important if the van does not have load sharing suspension,as any drop in drawbar height will reduce weight on towball,while raising the drawbar increase weight on towball.The change in towball weight with load sharing suspension is to little that is very difficult to even measure.Cheers
Its not an overly important number towball weight, too much time is spent discussing a weight that is only applicable before connecting to the tow vehicle.
The theroetical towball weight changes with the Yaw, Pitch and Roll of the moving combination, along with the terrain.