I've studied this problem for years, and am currently working on some
potential solutions. The Ackerman problem is only important for two
reasons. One, a correction would make the Tiger more enjoyable to drive on
the street. It would steer somewhat easier, particularly in low speed
activities such as parking and backing up. At higher speed the problem is
less noticable and "power" can overcome most of the shortcomings. The
second problem is related to the Fulcrum Pins and other front suspension
components. The Ackerman problem really increases the stress loadings on
these components. This is made even worse by the performance tires that
most of us run. The better they stick, the higher the stress loads become.
If you survey the failures of OEM pins that have occured, you will find that
almost all of them occured on "high performance" Tigers.
Lou's kit did help the problem, but it introduced several of its own.
Friction increased with each component, making steering somewhat harder, and
just plain road dirt wore out the articulating and rotating components very
rapidly. Even just a little wear made the system loose.
Jim is correct in his description of the two major problems in fixing the
Ackerman situation. The rack is two far forward, placed there to clear the
damper and pulleys, and the theoretical angle of the steering arms is too
small. That is they need to bend more to the outside. The problem here is
that their location is limited by the brake disks. Doanne Spencer resolved
this problem on the No. 55 Tiger by bolting the calipers on the outside of
the spindle and reversing the disks. He was also running Halibrand mags
with real Knockoffs, so he had more room to work with.
Any practical solutions still have to correct both of these locational
shortcommings in the original design. I've looked at several potential
solutions, none of which relate to leaving things "stock". The rack
location is restricted by both the engine and the bolts attaching the
crossmember to the frame. You can go lower and down with the engine, and
you could build a custom dampner with the mass in front of the pulley. This
would free up a gap between the engine and the pulley to locate the rack.
This would be pretty close to the optimum position. The front crossmsmber
bolts and the notches that give rack clearance require major work. This
continues to errode the stiffness of the crossmember which is already "weak"
in that reguard. The damper relocation could be made to work, but it brings
in the problem of crank stifness and brittleness. With a cast crank, the
new loadings could shorten crank life, with failures being very dangerous.
My current efforts involve lowering the rack below the damper. This is
really major surgery on the crossmember. I have one crossmember roughed out
for this test, but it will never see operation on the street. It could,
however serve as a design base for a tubular replacement crossmember. This
leads to replacement of other front suspension components such as the
"infamous" fulcrum pins. The spindles and brakes would be changed to
components that would allow optimization of the steering arm connection
location. I also have to get my SUN computer alignment machine fixed so I
can get functional data.
I'm going to be actively working on the Mustang Power Rack conversion for
Rob's Bomber in the near term and hope to get into the rack location
development later this spring. All things take time and I've only been
modifing my Tiger for 31 years so far.
Tom
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