AWD performance advantages - lengthy

[Andrew Fletcher <FLETCHA@citec.qld.gov.au>]

Hi to all,

I was re-reading parts of my "Audi Quattro Gold Portfolio" and came
across an interesting piece that contained information that perhaps some
owners weren't aware. And I quote (speaking of the urQ development)...

"Total weight penalty is 165 lb more than rear-wheel drive. And there is
extra friction from the extra drives and oil seals, so how do they manage
to save fuel. For a long time it was a mystery to them too. Prof. Piech told
me:'Our tests repeatedly showed that th car with four-wheel drive had a
higher top speed and used less fuel than the same car with two-wheel
drive. It took us a year to find out why.'

First they spent a million Deutchmarks on a test rig to measure the power
consumed at evert stage from the engine to road wheels. The results
contained no surprises. As expected, they were losing 1.5 to 3 percent
of power in driving the four wheels, about the same as they expect to
lose in an automatic transmission. Piech said: 'The secret must lie in the
tyres. There was nowhere else to look. But the tyre manufacturers
couldn't help. Their roller tests couldn't provide the information we
wanted.'
They finally got the answer from a test programme run on a rolling road
in an American laboratory, plotting the power consumed by a tyre
throughout it's operating range. A tyre which is driving the car consumes
power. A tyre under braking, or negative torque consumes power. But a
tyre that is rolling freeely consumes power to. The lowest power
consumption was recorded with the torque input experienced in a four
wheel drive car. A tyre taking the torque required for two-wheel drive
absorbed significantly more power and the total of two driven tyres
which were being pulled or pushed along, was greater than that of four
driven tyres. So given an efficient transmission , you have a sensational
revelation; four-wheel drive, in addition to all its other advantages, can
save fuel. The advantage increases with the power transmitted."

Compiled by R.M. Clark
ISBN 1 85520 3030
Brookland Books Ltd
PO Box 146, Cobham,
Surrey, KT11 1LG UK