Re: Porsche Handling

["Tim Hancock" <timhancock@domain.elided>]

Its time to introduce that little feller 'The Polar Moment of Inertia' into
the discussion as this physical principle has considerable influence on what
happens to any body in motion. In simple terms if you take a simple hand
weight with two sliding weights on each end it is easier to control twisting
the weights if the weights are close together. If you move the weights to the
extremities of the bar then there is considerably more inertia in the system
and it is more difficult to counteract and correct the twist. The fundamental
weakness in the rear engine concept is that instability is more difficult to
control as the weight is at the back and carries considerable inertia because
of its mass and is thus difficult to prevent from swinging pendulum style.

I can just about remember a little thing in physics called the parallelogram
of forces,and that certain little formula: Force = Mass x Acceleration. A car
in motion is a perpetually changing physical demonstration of this formula as
it accelerates, brakes or changes direction. The mantra "Always brake in a
straight line" simply expresses how best to apply the considerable forces
involved in a way that will introduce the least instability as the 'invisible'
Force arrows all point forward. If you brake at an angle i.e. in a bend, then
the Forces are still going straight on whereas the vehicle is trying to go in
a different direction, so the 'invisible' Force arrows are all coming out of
the side of the car...which is where the Mass of the vehicle comes into play
as in the Porsche example the Mass at the rear exerts a greater Force than the
Mass at the front. This applies just as much when accelerating or decelerating
as you are destabilising the moving body. This also sheds light as to why
vehicles travelling at a constant speed in a straight line show the least
tendency to fly off the road.

Whatever else you do to the vehicle is only an attempt at masking or
engineering out these fundamentals and I can only refer you to the engineering
officer of the Starship Enterprise..."Captain! ye canna defeat the laws of
physics" said Scotty on more than one occasion. So far at least he has been
proven right.


Tim Hancock  164TS Lusso  Boston UK

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