Re: [T3] Steering Question

[Simon Glen <simonglen@bigpond.com>]

Jim Adney wrote:
> >For a fastback I would inflate the tires to 19/27 psi front/rear. No more.
Since there is very little load on the front tires of our cars, they need very little
inflation there. In fact, quite the opposite is true: Anything over 20 psi is
overinflated. While this will not cause tire damage, it will cause poor road
holding and handling.   ....  it really would handle better and safer) with lower
front tire pressure.

>

A few years ago I had a totally standard unmodified 1970 Type36 Variant
or squareback (with constant camber CV-joint rear - so called IRS).  A well-
known motor racing identity here took this car for a test drive on the then
Australian Grand Prix circuit.  I sat in the passenger seat.  After the first lap,
he stopped and we changed the 165x15 Michelin tyre pressures from
19front/28rear to 32front/28rear.  I was astounded at the transformation.

What was a staid and risk-free safe understeering grandmother's car
suddenly became a vibrant oversteering car that was exciting but very
predictable to drive hard and fast, sliding perfectly through corners
under full power (the Michelins squealing for all their worth!).  I spent
the next hour on the race circuit enjoying my car to the fullest.

When I had to leave the race track and drive home, he advised me to
change the tyre pressures back to 19front/28rear because if there was
an accident on a public road and my "incorrect" tyre pressures were
discovered I could be in trouble with my insurance company.

VW have always specified relatively low tyre pressures for their rear-
engined cars in order to minimise the tendancy for them to oversteer,
something which the marketing people feel is not good for Joe Public.
They may be right.  In some parts of the world the early Beetle was
given the nick-name of "the German roller".  Porsche 356s were often
condemned for their oversteering as were also the big air-cooled V8
Tatras.  By the mid-sixties VW was fitting camber compensators or
"Z-bars" to its swing axle Beetles and Type3s all in the name of
making them safer for Joe Public.

Then, during the mid-1960s, Ralf Nader began to focus on Volkswagen.
VW was terrified that its rear engined swing axle cars would go the way
of the Chev Corvair.  It introduced expensive and what was then quite
sophisticated constant camber CV-joint drive/suspension in order to
further reduce the tendancy for a rear-engined car to oversteer.  In the
end it produced a car that was a tame predictable understeerer.  Now, if
Joe Public went into a corner too fast in his VW with constant camber
and low front tyre pressures he would instinctively lift his right foot up
and hit the brakes and his car would predictably slow down enabling
him to negotiate the corner more calmly and without going into the bush
tail first or even rolling.
In fact, with a rear-engined vehicle a driver should really do virtually
the opposite when approaching a corner too fast.  The last thing he should
do is hit the brakes.  He would have more control over the vehicle if he
was able to apply more power to the rear wheels encouraging the rear
to slip out.  This was how and why the early 1500S notchbacks were so
successful in rallying in Europe and Australia during the early sixties.
Like the Porsche 356s, the 1500S was an honest oversteering vehicle.

Nowdays, reversing the tyre pressures to 32front/28rear has the effect
of allowing the rear-engined VW to perform naturally as an oversteerer
- an enjoyable driver's car.  But, try telling Ralf Nader that is a good thing!

Simon Glen
Toowoomba, Australia




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