Understanding the dynamics of towing: Nose weight

ByRV DailyJuly 20, 2020
5 MINUTE READ
Understanding the dynamics of towing: Nose weight

In parts one and two of Understanding the Dynamics of Towing, we have established that the nose weight of your trailer plays a crucial role, here we discuss nose weight in detail.*

It does not matter if you have a single axle or twin-axle caravan, there are four things that need to be checked:-

  • The manufacturer of your vehicle will have specified a maximum nose weight that can be applied to any towing hitch installed on the vehicle.
  • The manufacturer of the towing hitch will have specified a maximum nose weight that can be applied to the towbar.
  • The manufacturer of the hitch fitted to your caravan will have specified a maximum nose weight that can be applied through the hitch.
  • The manufacturer of your caravan will have specified the maximum nose weight that can be applied.

For some vehicles, the recommended nose weight loading will be the same as the towbar loading as they are usually manufactured as OEM parts for the vehicle manufacturer. Sometimes though, the towbar might have been an aftermarket fitting, but might have a different nose weight loading to the original equipment fitted towbar. It is essential therefore you check both.

It is imperative that you check the limitations of the vehicle, towbar, hitch and caravan, before going any further. Write your figures in the following table:-

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In the examples, I will use typical figures, these may not be suitable for your vehicle and caravan combination! Once you have obtained the four values, you can now work out what is the maximum nose weight limit you can use. Here is an example:

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In this case, the maximum nose weight that can be used is 85kg. It is always the lowest weight in the table!

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With the caravan perfectly loaded and all the weight in the middle, it should balance on its main wheels… But this is not an ideal situation. The caravan is not stable and the slightest force acting on it will tip it one way or another. To stop this happening, an offset in the Centre of Gravity (CoG) is used, simply by loading the caravan with the weight slightly forward. For single-axle caravans, this is already done to some extent by the manufacturer when it designs the caravan. It will have been designed with a slightly forward Centre of Gravity.

We can calculate where to put the load inside the caravan to obtain the correct nose weight, but in practice, it is easier to just simply weigh the caravan at the point of the hitch. There are special gauges/towball scales to do this, but simply using a pair of bathroom scales and a short piece of wood placed between these and the tow-hitch can achieve the same results.

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Measuring the nose weight on any caravan or trailer should always be done on level ground. First, we need to ensure the tow hitch on the caravan is the same height as the towball on the towing vehicle to be used. This is achieved by simply adjusting the jockey wheel up or down. Make sure the caravan handbrake is ON!

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Next, we want to measure the height between the top of the bathroom scales and the underside of the caravan tow hitch. Measure from the scales to the underside of the hitch. If you intend using a section of broom handle so it fits inside the hitch, don’t forget to allow for this measurement.

Once you have the length, cut a piece of wood 50mm x 50mm section to length. It is now a simple case of standing the piece of wood on to the bathroom scales and slowly lowering the hitch on to it by winding the jockey wheel up. Don’t forget, you MUST chock the wheels first to stop the caravan moving and then release the handbrake BEFORE starting to lower the hitch onto the wood. “Why?” I hear you ask, well, if the handbrake remains on, the pivot point isn’t actually the axle, it is the point where the tyre touches the road surface and with the handbrake on all you will be doing is turning the wheel slightly to let the nose come down, it’s not actually pivoting and, if you chocked the wheels, it will not roll forward slightly and you will not get the correct reading on the scales.

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Once the jockey wheel is clear of the ground, you can now simply check the nose weight by reading what is on the bathroom scales. If the reading is higher than you want, lower the jockey wheel, apply the handbrake and adjust the load in the caravan by moving something forward of the axle back a little towards the rear.

Now let’s think about that for a moment. What could happen if, to get the correct nose weight, you have to move a lot of stuff to the rear, in fact too much stuff too far to the rear; what are the effects of this?

When being towed, all caravans have a tendency to sway from side to side, either due to undulations in the road, the effects of crosswinds, or more likely the effects of lorries and large vehicles overtaking.

Read more about: the effects of being overtaken by trucks

If there is a lot of weight at the rear of the caravan and the nose weight is correct, there is a fair chance there is nearly as much weight at the front of the caravan too! Having extreme weight at the front and rear is commonly known as the dumbbell effect, the correct term is Yaw Inertia. As the two areas of mass are further away from the pivot point, it has a tendency to increase in oscillation rather than be damped by the force of the towing vehicle.

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In order to reduce the dumbbell effect, it is essential to keep the mass towards the centre of the pivot point. It may mean just lying the awning on the floor directly above the axle, but in some cases, it might mean removing heavy items from the front locker and stowing them in the caravan or in the boot of the car. Moving any weight from the caravan to the towing vehicle is always a good idea. As a general rule, the heavier the towing vehicle and the lighter the caravan the easier it is to tow.

What nose weight should I use?

There isn’t a simple hard and fast answer to this. Nearly all the European motoring organisations, caravanning clubs and towing associations recommend the nose weight should be between 5% and 7% of the loaded trailer weight. Again, with some combinations of caravan and towing vehicle, the maximum nose weight specified by the vehicle could be less than the recommended 5% to 7%. (This is usually with a light car and a heavy caravan, but be careful, there are some 4X4’s that have a surprisingly low nose weight limit.) However, in Australia (and America) manufacturers prefer to follow the 10% of the trailer’s gross mass.

We aren’t going to debate that difference in opinion on this occasion, but that you follow the recommendations given by your vehicle and trailer manufacturer with regard to nose weight. The safety and stability of your set-up really are governed by not exceeding any limits and ensuring a balanced load following the principles we’ve outlined.

You may ask: Can I just load up to the maximum nose weight my car and caravan allow?

Yes, you can… but hang on a minute, let’s think about this. Remember back at the start we went through some of the forces acting on the towing vehicle. In the braking example, we decided that towing slightly nose down was the best option, and we discovered that under braking forces, the caravan imparted a downward force on the rear of the vehicle, well this will increase the nose weight and if you are loaded to the maximum nose weight permitted for your combination, the act of braking will take your nose weight over this limit. Most of the components are engineered to take more than the specified limits, but to continually exceed this under braking will contribute to increased fatigue on all the components, in addition, the over-run system will be subject to increased lateral forces and may not work as efficiently or as smoothly as the manufacturer intended. So be careful if you are loading close to the nose weight limit.

In the final part of Understanding the Dynamics of Towing, we look at other nose-weight-related handling issues you may encounter. Click here to read it.

*Note, as the article was written in the UK, the weight examples used are lower than typical in Australia. However, the laws of physics are universal…

This article was written by and reproduced with the permission of Simon Barlow at the Caravan Chronicles.