Why is it that an 8 ton truck tractor unit can tow a semi trailer
weighing up to 36 tons (for an all up weight of 44 tons) which is more
than 4 times its own weight, yet your average passenger car is usually
limited to towing something around its own weight give or take a few
hundred kilos. How come the descrepancy? Is it simply to prevent the
car burning out its transmission and brakes or is there another
reason?

B2003

In article a3a4daaeed4d@y38g2000hsy.googlegroups.com>, Boltar says...

Because that 36 tonne trailer has fully functioning suspension and
braking system, including ABS and even EBD, that are identical to those
used on towing units and are controlled by the towing unit. That means
the towing vehicle isn't having to brake the trailer as well...

"Boltar" yahoo.co.uk> wrote

Because it is designed to.

"Conor" hotmail.com> wrote

Yes, in a nutshell, it isn't a trailer, it is a semi-trailer and it is
*carried* by the prime mover, rather than being towed by it.

On 9 Aug, 18:13, Conor hotmail.com> wrote:

You can get braked trailers for cars. in fact most have seperate max
towing weights for braked and unbraked in the handbook.

B2003

On 9 Aug, 18:54, "Knight Of The Road" hotmail.com>
wrote:

Ok , what about doubles then in the USA and road trains in australia?
I'm not arguing , I'm just curious as to why cars have such a low max
towing weight as a percentage of their own weight.

B2003

On 9 Aug, 19:09, Boltar yahoo.co.uk> wrote:

Often it's because the towbar is so far behind the rear axle that a
heavy trailer (which has to be nose heavy for stability) reduces the
load on the car's front wheels too much. Since they do much of the
braking and all of the steering, that's bad news. Many (in random
stops it's generally 40 - 60%%) caravans are grossly overloaded, and
you can see this from the squat at the back of the towing car and the
very large gaps between the front wheels and the arches.

Ian

"Boltar" yahoo.co.uk> wrote

I presume their towing hitches are massively engineered, but in any event, a
truck has a chassis, which a car doesn't. A car's towbar is simply bolted to
a piece of 18 guage steel.

Well, the trailer on a wagon and drag HGV only weighs the same as the prime
mover too.

And if you try towing a heavy trailer with a light prime mover, you very
quickly find out why wagon and drags are also known as "dragon and wags"

"Boltar" yahoo.co.uk> wrote

Yes, but they are "over-run brakes"- the trailer's brakes are applied by the
trailer pushing forward on the towbar as the prime mover brakes.

It's an ingenious idea, but obviously nowhere near as efficient as a
multi-wheeled braking system operating on 120 psi of air pressure and with
brake pads the size of telephone directories.

"Boltar" yahoo.co.uk> wrote in message
news:da6b1bb1-b367-407c-9299-a3a4daaeed4d@y38g2000hsy.googlegroups.com...

Trucks have brakes and suspension designed to tow large trailers.
Cars don't.

Simple really