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The way I understand it is that an Alko towball is rated 150kg. The rating of the towbar may be different. The rating of the tow ball should be equal or greater than the rating of the towbar itself. This is called the 'S' rating. I'll have to check about the hitch itself. Here is a quote from some research I did last year.
"If you have an Alko hitch then you need a Class A50-X towball with a 'D' and 'S' Value greater than or equal to that of the towbar. A Class A50-X towball is an 'Alko-type' tow ball, but does not necessarily need to be manufactured by Alko. Alko only produce a Class A50-Xtowball with a rating of D = 17KN and S = 150kg. For most cars this should be sufficient
If you have a Discovery, or maybe other large cars, the towball rating may be higher. The Witter tow bar for my Discovery is D = 15.8KN, S = 250kg, so the S rating of the Alko manufactured tow ball is insufficient (being a lower rate than the tow bar). In this, and similar cases, one would need to have a non Alko Class A50-X. These Alko-type tow balls are available at most tow bar fitters or online from companies such as this http://www.western-towing.co.uk/acatalog/Towballs.htmlhere.
The S value of a tow ball/bar refers basically to the noseweight. Your caravan may only have a maximum noseweight of 100kg or less, but as far as I can work out, if your tow bar has a higher rating then your tow ball must be at least the same as the tow bar."
This may appear complicated, but I wouldn't be surprised if many folk who tow with a 4x4 are towing with a towball (Alko) that is under-rated for their tow bar.
Post last edited on 16/05/2011 11:54:17
------------- David
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