Mike Gigante wrote a while back >
> 1) The back is way too stiff - he suspects that the anti-tramp rods
> are binding up the rear end and preventing rear suspension movement
> (the rose-jointed rods were not parallel to the leaf springs).
And I answer with lightning speed (NOT):
This is a problem. If the front half of your leaf spring and the
anti-tramp rods (often called traction bars in the USA) are not parallel,
it turns your entire axle housing into a giant anti-roll bar. If the rods
are rose-jointed (Heim-jointed in the USA), the problem is much worse, as
there are no rubber bushings in the system to allow roll.
Even if there is no roll element, drastically non-parallel anti-tramp rods
will add stiffness to the purely vertical motion of the rear because the
rotation of the axle housing has to make the springs S-bend.
> He wanted to disconnect the anti-tramp rods on the spot -- I wasn't
> all that keen as there were simpler things to try first. I first
As odd as this may sound, I would be tempted to remove ONE of the
anti-tramp rods and try it out.. This would eliminate the
giant-anti-roll-bar effect. The one remaining anti-tramp rod would keep
the axle housing from setting up the rotational oscillations which cause
axle tramp (often called wheel hop in the USA) as the leaf springs snapped
themselves in and out of S-shapes. There are designs which use only three
levers in the longitudinal direction (trailing arms) to solve this
problem, but they of course put the third one in the center, attached to
the top of the differential. When there are only three trailing arms, a
torque is never realized along the axle housing to act as an anti-roll
bar. Your present system effectively has four trailing arms, the front
half of each leaf spring on the bottom, and the two anti-tramp rods on the
top.
> 3) the Panhard rod is mounted too high (in his opinion) -- he says
> that because the body mount of the PHR is underneath the boot/trunk
> floor, the roll axis is moved up to this point and is preventing
> weight transfer to the outside wheels.
Right. The front roll center of a Spridget is fairly low. The rear is
fairly high. This means the roll axis is depressed in the front. The car
tends to roll onto the front outside wheel. Lowering the rear roll axis
helps. The Winner's Circle rose-jointed Panhard rod from the USA is made
to mount to the very bottom of the leaf spring attaching plate on right
side, and to a low point on a special bracket on the left. The Panhard
rod thus becomes the lowest part of the suspension in this area. The
springs on a Spridget have enough sideways flex to make this change in
geometry possible. In fact, its primary purpose is to tame this sideways
springiness in a Spridget. It does a great job at that, and I recommend
the Winner's Circle bar to anyone planning on putting serious (fun,
actually!) lateral loads on a Spridget.
(I have heard that Panhard rods are best left off of MGBs, as the sideways
stiffness of the springs is much higher, but I have no direct experience
with MGB suspension tuning.)
For more information, ask on
wheeltowheel@abingdon.Eng.Sun.COM or
racefab@pms706.pms.ford.com
where the race-car techies hang out.
Phil Ethier, THE RIGHT LINE, 672 Orleans St, Saint Paul, MN 55107-2676 USA
h (612) 224-3105 w (612) 266-6244 phile@stpaul.gov
It's still hip to be octagonal. Whaddaya call the Lotus emblem shape, anyway?
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