Thread: Max Tow-ball weight?

It is generally 10% of the Towing capacity or ( 250kg for 2500kg) or what the manufacturer states. (In the manual and or on the towbar plate).

In general the greater the down weight the better the stability at high speed, up to a point of course.

I don't think it is "calculated". As Andrew says, it is either an arbitrary percentage of the maximum towing weight or is the lesser of the figures given by the car or tow bar manufacturer. As a specified figure it is quite a recent number - tow bars did not require any labelling until the mid nineties or thereabouts, and the figure is not given in any of the Series owner manuals (I have 1967 and 1981) and I don't think it is given in the 1985 110 manual (its in the car and its cold out there).

The tow bar manufacturer obviously gets their figure from the structural strength of their tow bar, the vehicle manufacturer gets theirs from the lesser of chassis strength and the effects on stability (in all cases there will be a wide safety margin to cover dynamic loads).

The actual desirable download will depend on a wide variety of factors, including whether the trailer has one or more axles, the towball to centre of mass distance, the height of the centre of mass above the fore and aft pitch centre and the tow ball, and the actual gross mass of the trailer. Ideally the download will be such that under no circumstances will there be an upward load, but in the case of a single axle trailer, particularly with a high high centre of mass, this is impossible to guarantee, and is difficult even with a multiple axle trailer, particularly one with load sharing suspension. (As most trailer instructions advise, the mass should be concentrated over the axle(s) but with a bias forward)

While the amount of download is very important for safe towing, I am not as sure about the maximum figure - the motoring world did without it for the first hundred years of its existence, and of all the trailer accidents I am aware of, none could be related to excessive download (most are obviously due to driver error, with a few due to coupling failure, most of these due to the coupling not being properly secured, and a few due to inadequate download). A few accidents have resulted from failure of the trailer's drawbar, but these are almost certainly due to overloading rather than excessive download.

John

minefield.....

safe towing they say 10-12% of the overall load should be on the ball.

manufacturers seem to pull recommended figures out of their butt as well as their recommendations re load levellers etc etc

you owners handbook should say what the acceptable downforce is, multiply to suit the 10/12% rule and you have the weight you can tow :P

drive a toyota and tow anything then they recomend load levellers, even ford F series trucks have the same manufacturers recommendation.

d3 with airbag suspension lr say no levellers, toyota with airbags they say must use levellers

coroners and insurance companies are really starting to enforce manufacturers recommendations...

how do you safely use a hyland hitch with load levellers ?

its a minefield....

I agree no-one seems to really know "why" you use the ten percent rule--

I am horrified at the thought of 250 kgs PLUS on the tow bar

it seems its ok to load up the rear axle at the expense of steering and braking????