On Sat, 9 Aug 2008 20:09:06 +0100, Boltar wrote
(in article
<54f187fd-01bf-40b0-9b1e-218d4a80d306@y38g2000hsy.googlegroups.com>):

As others have said, it's really a case of "designed for it" - trucks have
the weight to control it, a coupling arrangement that puts a fair bit of the
trailer weight on the tow vehicle*, the gearing to make it move, and the
coupled brakes to make it stop !

In the UK, you can tow an unbraked trailer up to (the lower of) half the kerb
weight or 750kg with a car - or any lower limit the manufacturer specifies.
With overrun brakes, that limit goes up to 3,500kg or whatever the
manufacturer allows - which is usually VERY much lower. The weight limit is
usually related to the ability to set off up a hill.

Now both my Land Rovers are plated** for a 3,500kg trailer, and I know plenty
that tow such weights (and, ahem, perhaps a tad more !) It is also possible
to have that limit increased to 4,000kg by fitting a suitable coupled brake
setup (typically air brakes). Personally I'm 'wary' of towing 2 or 3 tonnes
on overrun brakes - largely because they are so often 'badly maintained' (aka
"does f**k all" !) Trying to anchor up yourself, plus a trailer that weighs
more than you do but doesn't have any brakes worth mentioning can be
"interesting" - which wasn't the word that came to mind on one occasion while
sliding towards a blind T junction with a trunk road.

I actually have vacuum brakes fitted to the 110, trouble is, you just can't
buy bits to make up the trailer end any more (well not in this country). Air
brakes are on the agenda at some point - I've got as far as having a
compressor, just need to find some salvage bits to make the rest up.

* Note that the coupling is ahead of the rear axle (or effective combined
centre with more than two axles on the tractor). This gives enormous
stability gains compared with having the hitch hung out at the back in a way
that just invites the trailer to wag you.

** Most cars aren't plated, so just look in the owners manual - but be aware
that these are only manufacturers recommendations and don't directly carry
any legal weight. Exceed them however, and the police can probably do you for
indirect offences - such as having an unroadworthy vehicle by operating it in
a manner not approved by the manufacturer.
Commercial vehicles and many 'dual purpose' vehicles like Land Rovers are
plated - the plate shows the maximum axle, vehicle, and train weights. If you
have a plate then this is the legal maximum.

Of course, all this is subject to what you have on your licence - another
subject altogether !