Tow cars and trailers

Dan G wrote:
I think it's important to be clear what we're talking about here. A VW
Passat TDi station wagon has a combined mpg of 48 and a long-run mpg
of 58, with 236lbs/ft of torque at 1,750rpm. The car has a kerbweight
of 3,500lbs and using the figure of 85%* of kerbweight to give towing
capacity, that allows trailers of up to 3,000lbs to be towed
comfortably.

*85% kerbweight - with 7% of the trailer's weight on the hitch or the
tow car's maximum, whichever is lower - is the maximum safe weight for
good stability, arrived at by the University of Bath in the 1990s when
they did instrumented testing and model simulation of tow cars and
trailer combinations.


Dan


Closed Trailer with a Std Cirrus in it is 680kg (54% is easily inside the
85%)The sail effect is a bigger decider for me - the trailer can push a smaller
car around when you are exposed to gusts at speed.

Hatchback weight is 1250Kg. Tows happily at the national speed limit, although
it does get a bit hard work in the mountains. Tops of our passes are around
2,300m MSL Nothing too bad for the small car to tow. Then I got into a Kestrel
T59D with one piece wings. It's trailer is unaerodynamic, heavy (900Kg) and
just plain huge.
The stability issue is in a different class. With nearly 2 tons of Wales' best
(XC70 is made in Wales not Sweden) and a really big polar moment on such a long
vehicle, the disturbance from trucks and wind is a lot lower. Fuel consumption
is not that different towing the trailer between the two - unless you get
irresponsible/inattentive with the speed. The control reserve is generally
bigger with the bigger car.
So stability is the primary towing reason for getting the barge - the other
reasons are indefensible. (It's hard making a logical case for something that
comes down to - "I like it".)In town the hatchback is the place to be - on the
open road or dirt roads the Volvo is a far nicer ride.

Cost - @ 2l/100km additional fuel is around 400litres per year. (roughly 100US
gallons)At ~R7/l (4USD/US gallon) that is quite a lot of money. In South Africa
the cost of my vehicular extravagance is equivalent to at least one tow per
month. I winch launch so the extra fuel for the trip to the airfield is close to
the cost of a winch launch.