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DIY Vehicle Weighing

  • Fyko van der Molen
    Fyko van der Molen on

    I’m planning to move to smaller, lighter SUV in the near future. I haven’t made a final decision yet, but I’m seriously looking around.

    What I see happening is that the weight factor of the trailer is going to be a lot more important than before. If the gross of the trailer must be less than the Tare of the car then I need to know the actual of both. I want to weigh the car and I want to weigh the trailer. Not just once, but every time.

    Several posts back there’s some info about a home-based weighing device. I need something that will tell me the actual weight of my car, the actual weight of the trailer in toto, and the weight on the towball.

    Please supply more info.



    As with yourself an increasing number of fastidious motorists are concerned with the actual weight of their towing combinations.

    Since there’s no easy way to get this information, particularly when you are ready to hook on and hit the road, we did some thinking and came up with a viable (but not particularly cheap) solution.

    To save me the effort of typing it all again I’ll give the link to the complete webpage here:

    Briefly, you have one device that you can use to weigh both your vehicle and trailer axles individually. You attach the load cell to your trolley jack and lift the axles clear of the ground one at a time. This process takes about 10 minutes.

    You then have your complete car and trailer weights before you.

    The same load cell will accurately determine your towball weight, either directly under the towball, or via the jockey wheel stem with a correction applied to derive the towball weight. This takes just a little mental arithmetic.

    You can now figure out whether you are within legal (and, more importantly, prudent) weight limits. Especially whether the trailer actually weighs less than the car, and by how much.

    I won’t do any marketing here but the cost is going to be around R2.5K, depending. Availability varies but is often disappointing, I’m sorry to say.

    Dan Perkins
    Dan Perkins on

    Does this device have its own internal power source? How long is the battery life?

    Fyko van der Molen
    Fyko van der Molen on

    Providing this unit with an integrated power supply would increase its cost by up to R1000 without conferring any real benefit since it would still be tethered to the load cell by umbilical cable. Plus there would be another thing to keep charged and another battery to replace in time.

    Since it is always operated in proximity to a vehicle its a simple matter to run a trailing power cable to either:

      <li style=”text-align: left;”>The cigarette lighter plug in the car,
      <li style=”text-align: left;”>One of the 12V Hella outlets in the trailer,
      <li style=”text-align: left;”>The 50A Anderson plug at the tow ball,
      <li style=”text-align: left;”>The 50A Anderson plug at the trailer’s tow hitch,

    If none of these are available then we make a cable wired to the Tail Light connector of a trailer plug. Switching on the parking lights on the car then powers the unit through the trailer plug. All of these solutions are available for less than R50.


    Joe Mattisson
    Joe Mattisson on

    What happens if I have a 1 ton load cell and I jack up under an axle weighing more than 1000Kg?

    I have a 2-tonne jack and I think my back axle on the bakkie should be less than a ton, but I can’t be sure till I weigh it.

    Fyko van der Molen
    Fyko van der Molen on

    Load cell makers quote 2 values in their specs:

    1. Safe overload,
    2. Ultimate overload.

    They all seem to agree on Safe Overload as being 150% of FS (full scale) but Ultimate Overload varies between 200% and 300% of FS.

    To me Safe Overload means that weight readings may not be linear anymore, and Ultimate Overload means that any more weight may damage the device.

    So if your axle weighs 1500Kgs you won’t be hurting anything.

    And depending on the frame style (shear beam or pancake) there may be a direct 2000Kg replacement available, meaning you bolt it on without any other modification and just change the setup in the controller, which takes less than a minute.

    Josef Konrad
    Josef Konrad on

    Being a bit of a skeptic I cut a wooden rod to go between tow hitch and load cell.  I don’t trust this calculation on the jockey wheel weight.

    If you pull the trailer brakes there’s no tendency for tow hitch to swing away and if the load cell is not on a slippery surface it won’t skate away.


    Exactly what the calculated offset using the jockey wheel weight gives.

    And weighing the jockey takes no time at all, and involves no danger of anything falling.

    So, now I’m a believer. Just like the MONKEES when I was a youngster.


    Athol Hughes
    Athol Hughes on

    The procedure I follow is like this:

    1. Jack up the front axle and read the weight (takes 5 minutes)
    2. Jack up the rear axle and read the weight (another 5 minutes)
    3. Add the 2 for gross car weight,
    4. Read the jockey wheel weight (and reduce by 10% to correct).
    5. Hook on,
    6. Jack up the middle of the trailer axle and read the weight
    7. Add the towball weight to the trailer axle to get gross trailer weight

    I now have the gross weight of the car, the gross weight of the trailer, the actual towball weight and its ratio to gross trailer weight. All the legal and insurance requirements taken care of.

    It took 15 minutes, I did it in my driveway, and it cost me nothing (aside from the R2600 initial purchase). Hard to beat.

    PS. I was in my last year of high school when that song came out.


    Fyko van der Molen
    Fyko van der Molen on

    It’s nice if you have 2 live axles on your car and a beam axle under your trailer – you find the centre of weight and lift it.

    With vehicles that have wishbones at the front you can normally find a chassis member between the front wheels that’s as good as a live axle for lifting on the axis of the front footprints.

    Independent suspension at the back can be a bit problematic because there’s often a fuel tank between the wheel centres. In this case you need to get as close to the footprint as possible, and accept that there will still be a small degree of error.

    Trailers with single rubber or beam axles are similarly very convenient but swing arms create a the same situation as you have with the car – you need to get as close to the footprint as possible. In the past we’ve produced a variety of drive-on plates with the load cell centralised below; none of them particularly easy to use since you need to raise the wheel onto the plate, either by driving on or lifting and lowering.

    Tandem axles pose another problem – lifting on the front axle will overread on the scale, and lifting the back axle will underread. The best is to lift both the front and back axles, one after the other, add the 2 readings together and divide the sum by 2.

    Note that you need a 2000Kg load cell to do this with accuracy. They don’t cost anymore than their 1000Kg brothers, but they need a more robust mounting frame.

    Fyko van der Molen
    Fyko van der Molen on

    Now also available in an all-white enclosure

    Simon Tasman
    Simon Tasman on

    What sets a Jimny apart is that any trailer heavier than 350kg MUST be braked.

    It can handle a trailer gross weight up to 1350kg max, but the usual 750kg limit for unbraked doesn’t apply. It’s 350kg.

    And 75kg max on the towball.

    So having the means to weigh your vehicles at home helps a lot. I hate to think what I was loading before.  At Clarens I saw a lot of guys getting it very wrong.

    Atholl Hughes
    Atholl Hughes on

    Realistically with a Jimny you’ll never be towing an unbraked trailer, since it’s difficult to imagine a trailer that weighs less than 350kgs being at all useful.

    While the max trailer capacity of 150kgs seems very generous for such a small SUV it comes with a major caveat: The towball weight may be no more than 5kg – which is 5% of gross trailer weight.

    To not exceed the 75kg towball weight limit (and I’ve seen first hand the consequence of doing so) requires lots of very careful positioning of the load. The way we do this is raise the towbar to towball height with the load cell under the jockey wheel and Anne calls out the adjusted weight (being a woman she can do mental arithmetic) as I shift things about.

    When the readout says 77kg, which is 70kg plus 10%, we lock everything down and hook on.

    We can also measure the gross weight of the trailer but we don’t need to do this every time because we know it won’t go much above 1250kg with what we load into it, but it’s nice to make sure occasionally.


    Dan Perkins
    Dan Perkins on

    It’s unfortunate that there’s a 6 week delivery delay though.

    Nothing available this year.

    Fyko van der Molen
    Fyko van der Molen on

    We support quite a wide variety of load cells, and can keep only a limited stock of each.

    If we have the unit you want then delivery is virtually immediate, if we have to get it in the delay is a few days to a couple of weeks, depending on where it’s coming from.

    So 6 weeks is more than twice as long as anyone has had to wait. I have before me a list of clients we’ve made happy, and another list of those that dithered until it was too late.

    Fyko van der Molen
    Fyko van der Molen on

    There’s been a few requests from people who would like to read the tow ball weight while they’re inside the caravan moving stuff about so as to get the nose weight within an acceptable range. This is not possible with the LCD unit tied to the vicinity of the tow hitch, and you need someone there calling out the weight as it changes – not 100% convenient.

    We now offer an optional (low-cost) Bluetooth extension that communicates via our standard cell phone app (which is free). This app allows you to read whatever is measured by the load cell on your phone, so you can move some weight inside the caravan, move to stand over the axle, and read the exact weight that the tow ball will carry once you hook on.

    The same app allows you to enter the gross weight of the caravan so that the towball weight can be presented as a percentage of gross. Preference of this ratio vary but it’s mostly between 7% and 10%.

    The background colour will also change from green to red when the towball weight moves out of the regulation 20kg to 100kg bracket, as specified in the law.

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