Are towbar motorbike carriers safe?
QUESTION
Hi John,
I have a question and need to know how to make sense of towball weight limits.
Reason being I'm looking for a SUV style vehicle and it must be able to carry on the towball at least 160kg. I'm not towing a van or trailer, I'm going to be carrying a dirtbike on a carrier. The info I have found says the ball weight is approximately 10% of braked towing capacity, so if I go with something like 2000kg braked I should be ok, right?
Dirtbike is 116kg (dry weight) and the carrier unit is 25kg, plus fuel of 20kg.
This youtube link will explain what I'm talking about, as in the carrier unit: https://youtu.be/4fiJzljfimg
Then I found this on the Nissan Pathfinder Ti and got totally confused. How is it variable? Weight is weight, unless it's not!
It has a GVM of 2715kg, a towing capacity of 750kg (unbraked), and a towball download limit listed as 100kg (if loaded vehicle mass is 120kg below GVM), 150kg (if loaded vehicle mass is 210kg below GVM), or 200kg (if loaded vehicle mass is 300kg below GVM).
I'm hoping this will appeal to the engineering head on your shoulders.
Kind regards,
Paul
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ANSWER
Paul,
I’m not exactly a free consultant mechanical engineer for punters - mainly because I’m not insured for it, not because I don’t want to be helpful. But I am alspo philosophically opposed to applying my training for free, one-on-one. I’m sure you understand.
The following comments are therefore general in nature, and definitely not advice.
Weight isn’t weight, frankly. A towball download limit is a limit ONLY in the context of towing a trailer. Download helps with trailer straight-line stability.
Trailers impose particular kinds of dynamic loads on vehicles. The loads pivot on a ball. They don’t transmit very much torque.
A dirt bike hung off a towbar has the capacity to impose very different loads - especially transverse horizontal bending moments, which, frankly, towbars might be inadequate to restrain. It’s a lot of torque when you go over a bump, dude. How to bend your ute: The truth about chassis snapping >>
Your information about 10% of tow capacity is wrong. For many vehicles it’s five per cent.
Frankly I think you re a nut if you do this. You could easily damage the vehicle and/or the towbar. And kill someone. Apart from that, great idea.
Buy a trailer. A nice, light 6x4 jobbie will be fine.
JC
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