Car towing capability

UK legislation calls it "kerbside weight", and that is most definitely defined, but I think it is safe to assume that this is the same as the kerbweight that we are all talking about. The legal definition ties up with item 2 above. A written definition in line with item 1 does not exist. However, few if any manufacturers specify kerbweight figures according to the legal definition. It is far more common for them to quote mass in running order, even if they call it kerbweight. By virtue of the differences in definition, mass in running order is invariably somewhat less than kerbweight.

Perhaps you could provide evidence that my comments should be accompanied by a health warning. Not following a recommendation doesn't automatically imply that it is dangerous not to follow it. It just means that one must be aware that more due care than usual must be taken.

On the level and uphill gradients, I would agree.   The problem becomes more apparent on long down hill gradients where the trailed vehicle becomes the dominate force in the combo.

Usually this causes fish-tailing, which is unpleasant at best, and lethal at worst.  There is little space for manover on most motorways if this starts to happen, and the motoring public are ignorant of what can happen when this action starts.  I have seen white vans over taking, not useful as the bow wave makes matters worse, to Lorries  backing off in anticipation on what could happen.

A number of vehicles are plated up to tow 3 to 4 tons.  But they are work vehicles used on private roads or areas of work.  If used commercially on public roads, different obligations lay with the driver, owner and insurance company, small groundwork contractors pulling excavators on trailers come to mind. 

Towing 3 tons at 60 mph with Defender, Jeep, (other makes are available) would be heading for a polite enquiry from traffic plod.  Assuming there is one working in the county, rather than sitting watching NPR read outs.

Rgds

Lornalou's argument was based on the stopping, i.e. braking, ability of the caravan which remains regardless of whether it is on the level, uphill or downhill. Your comment is centred more around the stability of an outfit going downhill. There is no doubt that stability suffers when going downhill, especially when crosswind is experienced at the same time. In particular the French have shown appreciation of this fact by applying speed limits for vehicles towing trailers on many downhill stretches of their motorways. So long as this is understood and drivers act accordingly by slowing down to suit prevailing conditions, there is no reason why manufacturers' towing limits can't be used to the full, even if these limits exceed 100% of the car's kerbweight. After all, unless they specify further restrictions to the contrary, such as for commercial use mentioned above, the limits that they specify apply just as much to the use on public roads as they do to private ones. There is no reason why the plod should question the driver of a Defender towing a 3000kg trailer at 60mph unless that speed were inappropriate for the conditions.