GrizzlyBathplug said:
Enjoy your vacation Ste6t9, hope everything goes well.
ProfJohn
I am having a dilema at the moment regarding nose weights.
I towed from Biddulph to Tywyn (wales) approx 300 mile round trip, with a nose weght of approx 110-120kgs, & van was very stable.
On getting home starting researching weight limits on Car, Van & towball.
The car has a limit of 140kgs, the Brink detachable towbar has a weight limit of 175kgs, yet the Alko hitch says in the manual 100kgs max weight.
When we towed caravan with said nose weight above, there were no problems at all, everything felt stable & sure, but am i putting too much strain on the Alko unit.
Apolgies for putting this in someone elses thread, but seeing as its a live chat at the moment, would like to get it cleared once & for all.
Thank you
Grizzly
Hello Grizzly.
Nigel has pointed out the discrepancy in your figures and as a result it will be unnecessarily wearing things out, but there are other concerns as well. You must never have a static nose load that exceeds the capability of the weakest link in the chain of equipment - in your case 100kg for the coupling head.
For simplicity in this comment I will continue to use kg to express the value of a force, though technically I should be using Newtons which are the scientific unit of force
Probably the biggest concern is safety, and that relates to the fact that if the overrun brake mechanism is overloaded it may not slide properly reducing of even preventing the caravans brakes from applying properly or even not releasing correctly.
Another point is the car and caravan manufacturer will be very much aware that the static nose load is actually very much smaller than the actual load that motion and vibrations creates when towing.
To put this into perspective, a company I worked for took a car and caravan to the Motor Industry Research Associations (MIRA) test track in Nuneaton. The caravan was loaded with accelerometers to measure the effects of towing over a number of different surfaces on the structure of the caravan whilst it was being towed. The results showed that even when towing over normal roads the vibrations typically created accelerations up to 4G (4 x the equivalent force of gravity but in many different directions) and on potholes and other severe road surfaces peaks of 8G frequently occurred. There was a 12G recorded peak on one run but it was not repeatable.
What this means is a static mass of 1kg could produce impact loads of up to 8kg force when subjected to an impact when the caravan was towed over a pothole.
Manufacturers will be aware of these sorts of results and will have specified their cars, towbars and couplings etc. to cope with these types of momentary peak loadings. A car that is continually subjected to 4G impact loads will wear, which is why things need servicing or like springs and dampers periodically need to be replaced. The balancing act is to design enough durability for the vehicle to withstand these typical loads for a reasonable length of time (just longer than the warranty period). A car that is subject to higher G forces will wear more quickly, and early failures may be challenged by the manufacturer with suggestions the car has been used in a manner for which it was not intended. Ultimately too much load will cause a component failure before its expected life time is reached
I suggest If your coupling head is rated for a static load of 100kg, it should withstand the peak loads of 400kg generated by towing with ease for the normal life of the product. If it is subjected 800kg impact loads it will reduce the time before significant wear becomes apparent.
However if you are overloading at 120kg, then the system will be seeing 480kg quite often which of course increases its rate of wear and on peak 8G loads at 980kg that is 180kg extra load on the components and that will be rapidly adding extra wear and potentially taking the system into its potential failure area.
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