To those interested in Panhard locations, here is my analysis to answer some
of the recent questions.
The stock Mark I rod runs from below the wheel centerline of the axle on the
left side to high on the body on the right side. The Mark II runs the
opposite direction. The instant roll center of the rear suspension is defined
as the point at which the Rod intersects the centerline of the car.
When accelerating out of a RIGHT turn, the body rolls to the left, raising
the right pivot. When this happens the instant roll center of the rear rises
increasing the roll stiffness of the rear suspension. Two things now happen.
The engine torque into the rear axle as well as the increased rear roll
stiffness cause vertical loads to be shifted from the right rear and the left
front tires to the left rear tire. As the left front and right rear tires
lose vertical loads they lose cornering power. These cornering forces are
additive and transferred to the left rear tire. As the force exceeds the tire
capability there will be an extreme oversteer in right turns and lifting and
spinning of the right tire.
When accelerating out of a LEFT turn, the body rolls to the right, lowering
the right pivot. When this happens the instant roll center of the rear
suspension lowers, decreasing the roll stiffness. Again two things happen.
The engine torque into the rear axle as well as the decreased rear roll
stiffness causes cornering force capability to be shifted to the right front
tire. As the force exceeds the right tire capability the car will have
understeer. Having a car that handles different when turning left or right is
not fun.
With the Tiger Mark II, which has the Panhard Rod running from the right side
of the axle to the left side of the body, the opposite dynamics happen and
these loads subtract from each other. The left and right turn differences are
improved and it is easier to balance front and rear roll stiffness.
So, to improve the Tiger rear geometry in order of complexity, you can change
the Panhard Rod to the Mark II design, make the Panhard Rod horizontal by
lowering the frame attachment pivot or install a Watt's linkage. Good luck in
finding room and feel free to add more ideas.
John Logan
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