Thread: Towing and ball weight

I think the 10% applies to single axle only

10% is the maximum reccomended... I personally aim for as near to perfect balance as possable. IE you should be able to easily pick up the draw bar with one hand.

-Ve loading (ie the hitch wants to lift up off of the ball by itself) is bad.

Good post Taz
Im interested in the same info for my new trailer Im building,as its strong enought to cart a tank!!!!.
YOU HAVENT SOLD THAT CAMPER TRAILER HAVE YOU!!!!
Andrew

My understanding of the 10% rule is that its applicable up to - in your case the max download allowable on your towbar of 150kg . IE a 1200kg van should be 120kg for example or 1000kg 100 download.
At the end of the day you should experiment and settle on whats most effective.
David

The 10% is a rule of thumb only. The situation is not as simple as any rule of thumb can cover. As Dave says, the thing that is really bad is a negative load on the ball, but it is not just the load that is a problem.

One critical factor is the position of the trailer's centre of gravity relative to the towing point and the wheels - it needs to be as far forward as possible without excessive download on the towbar - and definitely in front of the trailer's wheels. The ball load is simply a measure of the position of the centre of gravity. With a tandem or triple axle trailer, it is less critical as the trailer is inherently stable, although it still wants to be in front of the centre of sideways resistance of the set of axles.

Another factor is how high the centre of gravity is - and the higher it is, the further forward it needs to be, to make sure it is always forward of the wheels despite hills and bump effects. Also, the longer the distance from the towing point to the trailer wheels, the more stable the setup is, and the less lead is needed on the centre of gravity.

A separate consideration is the effect of the ball load on the towing vehicle - and the maximum this can be allowed to get depends on the vehicle mass, its suspension, and the distance the point is behind the rear wheels, and, of course, the strength of the towbar. Again, a negative ball load is not a good idea.

And a final consideration is that the traditional ball coupling is far stronger with downward force than with upward force, making another reason to avoid negative ball load, and to have enough down load that it does not become negative even on bumps - how much is needed here depends not only on the height of the centre of gravity of the trailer, but the distance between it and the coupling.

So I see in summary - 10% is a rule of thumb only; you might want to consider even increasing it for short, single axle trailers with a high centre of gravity, but significantly less would be quite OK with a long tandem or triple axle trailer with a low centre of gravity.

As a final note - yesterday near here there was a collision between a car and a B-Double killing all five in the car when it hit the fuel tank of the truck, went under it and burst into flames. The car was towing a trailer (6x4 box), which is reported to have started to snake when the driver of the car abruptly thought better of an overtaking attempt, causing the car to lose control and hit the side of the B-double travelling in the opposite direction. It would be interesting to know how much download was used on the trailer coupling, but it does emphasise the importance of the matter.

John

Hi Taz - I agree with John above
I would recommend that you get as much weight on the ball as possible (your legal limit of 150kg). When I purchased my boat (gvm 2.8t) it was set up with less than 20kg on the ball and at speeds over 80k was downright dangerous, would get side to side swaying up big time. As boat trailers are adjustable we moved the axel assembly back (only about 6 inches) resulting in just under 250kg on the ball – completely transformed the setup – very stable at 100 -110k and high side winds. As I understand it, the theory is that a balanced trailer will act as a see-saw - both up/down and side/side resulting in the trailer (which is heavier than the tow vehicle) getting a mechanical (leverage) advantage over the car. This is compounded by the short wheel base and relatively big rear overhang (compared to wheel base) on the disco.
Think of a semi. An 8t truck can tow (with excellent stability) 35t of trailer – the “ball weight” is around 40%, and no overhang (actually negative) from truck rear axle to hitch point – massive distance from tow point to trailer axel – resulting in no leverage (see-saw) advantage. There are equations that mechanical engineers use for this and it involves:- 1 distance tow point to rear car axle, 2 distance tow point to trailer axle, 3 wheel base, 4 the %trailer weight on tow point. That’s why the US is big on 5th wheel trailers – they work on 20 – 30% ball weight. I think it is pretty much also agreed that a trailer (say camper) tows much nicer with a long draw bar also fitting these equations.
You can’t do much about the relative leverage advantage distances – except stretch the draw bar, but you can improve the equation easily by getting weight on the tow vehicle – a seesaw doesn’t rock with an extra 10% weight on one end.
The 10% rule is what the engineers recommend for all trailers hitched to a tow point aft of back bumper (ie standard towbar - not 5th wheel) provided vehicle spec allow it – if not recommended is max.
6% will be much better than 0-1. If in doubt have a chat with a respected heavy tow dealer.

I keep a load on the towbar to prevent the trailer wagging. I wouldn't go over the 150kg though as the chassis will crack at the coil spring perches if you hit anything too hard. If you've got 2500kg on the back and it starts to wag, then I'd be slowing down - sadly, but from my experiences it's ok. I also generally guess ball weight judging by the rear ride height and amount of drop in the suspension.

Slunnie
Ive already cracked my chassis where the rear x member welds on BOTH sides.
YEP IVE TOWED ALOT OF HEAVY LOADS!!!!!
Thats why I have 2 Stage1s sitting in the yard waiting to build a firewood mule from!!!!
Andrew