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Welcome to my newly
redesigned Fiero 2M4 resource site. The original site recorded over
12000 visits, hopefully this one will also prove as useful.
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Original
Title :
ALL
FIRED UP!
The
following article is an excerpt from a 1991 Kit Car magazine article from
Herb Adams VSE. I have only included the suspension information.
Herb
Adams was a GM engineer who went on to produce some of the best handling
"massaged" Pontiacs of the 1970s to 1990s.
FROM
THE GROUND UP
Making
a standard production car handle well on the racetrack often requires a
variety of modifications. Each change is aimed at correcting one or more
problem areas. You should start from the ground up by selecting the
right tire sizes.
The
basic handling problems any rear- or mid-engine car is that the center of
gravity is behind the traction center of the tires. Rear-engine race
cars compensate for this by using larger tires on the back and smaller tires
on the front. This moves the traction center to the rear so it is on, or
behind, the center of gravity. You can use larger rear tires on your
Fiero for the same benefit. The stock rear fenders have room for
Goodyear ZRS 255/50x16 tires on 16x9 wheels, although 225/50x16 tires on 16x8
wheels will also provide improvement.
The
basic stability of your mid-engine Fiero can also be improved by moving the
center of gravity forward. The easiest way to do this is to move the
battery from the rear to the forward luggage compartment, or fit it ahead of
the right front wheel well. The latter location requires more work, but
it does preserve some of the limited storage space.
BEEF
UP YOUR BUSHINGS
The
rear control arms on a stock Fiero are mounted the the frame with rubber
bushings. They allow the rear arms to move forward under power and
rearward under braking, and the effect on handling is a change in steering
direction whenever the throttle or the brakes are applied. The other
problem with the earlier Fiero rear control arm bushings is that they deflect
inward during cornering, which changes the rear wheel camber angle. Both
of these handling problems can be corrected by replacing the stock rubber
control arm bushings with steel bushings.
Steel
bushings are required for this application because of extreme loads resulting
from driving and cornering forces. I have found that the only bushings
that hold up are aircraft-quality hardened steel on hardened steel mono-balls.
Steel sleeves must be welded to the control arms to secure the mono-balls in
place. This operation requires that the rear arms be removed from the
car. The installation takes time and money, but are well worth the
results. Changing the rear control arm bushings is the most significant
change that can be made to improve your Fiero's handling. *
When
the rubber is removed from the rear control arm bushings, there is potential
for more ride harshness and road noise. This is usually not a problem
because the rear subframe is still mounted to the body with rubber mounts.
If
you want ultimate handling on the racetrack and you're not concerned about
noise, you can replace the rubber subframe mounts with steel or aluminum to
keep the subframe from moving in relation to the body. The handling
improvements gained by this modification are less than when the control arm
rubber is removed, but it does provide some advantage on the racetrack.
The
front control arm bushings are also mounted in rubber so they deflect when
cornering loads are applied. If these bushings are replaced with steel
and nylon bushings, there is a noticeable improvement in front-end cornering
power. Since the weak link in the Fiero handling is not the front
suspension, and because there is less weight on the front end, changing the
front control arm bushings is not recommended unless race ready handling is
desired. The arm must be removed from the car to replace the bushings.
NEUTRALIZING
UNDERSTEER
Besides
the rear control arm bushings, adding and/or changing the stabilizer bars are
the most significant handling improvements you can make on your Fiero.
Due to the Fiero's inherent tendency to spin-out at the limits of its
cornering power, Pontiac engineers tuned the cars handling characteristics to
provide an excessive amount of understeer. This trait ensures safe
handling for the majority of drivers, but does not permit fast cornering.
The stock Fiero uses a front stabilizer bar and no rear stabilizer bar to
create the desired understeer. If your Fiero has steel rear control arm
bushings, its rear suspension is capable of absorbing more cornering force, so
some amount of rear stabilizer can be used. I have found that by
increasing the effectiveness of the front stabilizer bar, we can use a
large rear stabilizer bar. By matching the size of the front and rear
bars, it is possible to make a Fiero handle with neutral steer instead of
excessive understeer. Neutral steer provides the maximum cornering speed
because all the tires work at the same level. Large front and rear
stabilizer bars limit the body roll angle and positive camber, which keeps the
tires from losing cornering power
The
use of large front and rear stabilizer bars doesn't have any significant
effect on ride quality or road noise. The addition of the front and rear
bars will also make a significant improvement in steering response and
precision. The 1.25 inch diameter rear bar recommended by my company,
(Herb Adams VSE, Dept. KC,23865 Fairfield Place, Carmel, CA 93923
408/649-8423) is tuned to be used in conjunction with a one inch front
stabilizer bar. Do not use a rear bar without the front; doing so will
result in oversteer, which can be dangerous.
Using
a larger front bar improves the steering precision, allowing removal of the
stock steering dampener. The Fiero dampener reduces steering wheel
kickback and vibration, but with a more effective front stabilizer bar, these
problems are minimized so it is no longer needed. Removing the steering
dampener also allows the steering wheel to turn faster for improved handling
and overall control.
SPRINGS,
SHOCKS AND OTHER STUFF
Spring
rates on stock Fieros are correct for most purposes, but the problem is that
most of these cars are too high off the ground. The best way to lower
either the front or the rear is to cut the existing springs. By cutting
half a coil off a spring and reforming the ends, you can lower your fiero
about one inch. Lowering the car reduces the available ride travel, but
for most driving conditions, there is no loss of ride quality. with Koni
adjustable shocks and struts, you can tune the ride quality in relation to to
improved handling.
The
brakes on an '88 Fiero are extremely good even on the racetrack.
Unfortunately, it's not an easy conversion to mount the '88 brakes onto an
'84-'87 Fiero. This means you will have to suffer with the barely
effective brakes now on your car. I have tried many things to improve
the stock brakes, but there doesn't seem to be an easy solution.
Semi-metallic pads offer some advantage for a limited fix. **
As
for chassis reinforcements, the basic Fiero structure is heavy and pretty
stiff. I didn't notice any structural improvement after installing a
rollcage for racing purposes, so I don't recommend this modification for
street use.
GETTING
A LINE ON ALIGNMENT
The
camber adjustment on the front of a Fiero is accomplished by rotating the
upper ball joints from front to the back. The ball joint is offset
between the mounting bolts so you have your choice of two positions. For
the best handling, you want the position that gives the most negative camber.
Usually this isn't much, so you'll need to move the holes to get more. I
don't recommend more then one degree of negative camber for street use.
For
more caster, move the spacers between the upper control arm and the frame
bracket, positioning the upper arm as far back in the car as possible.
You only need one degree of positive caster to have good handling and you can
usually obtain this by moving the spacers on the Fiero.
As
for toe-in, it should be 1/16-inch at the front to provide good control and
stability under braking. Rear toe-in is set by turning the rear tie
rods. It's important to have between 1/16-inch and 1/8-inch toe-in at
each rear wheel. Measure each rear wheel in relation to the rocker
panels when determining rear toe-in. If you measure one wheel versus the
other, you can end up with the proper toe-in, but the car will probably
dog-track.
For
setting rear camber, move the shock strut slotted hole where it connects to
the rear upright. For street driving, you want at least one degree of
negative camber; for racing, you need about two degrees.
To
read more of this article and one owner's commentary on it click
here.
*
,**,
Many of the recommendations given above can be applied to any street driven
Fiero, they are, however, somewhat severe for daily driving.
Polyurethane instead of steel bushings would be more streetable although poly
bushings can cause binding and lots of squeaks and groans from the suspension,
and the 84-87 brakes can
be converted to vented GA type parts. (This article did date from 1991)
Remember, Herb Adams is a master of chassis engineering and following
his lead will produce a far better handling Fiero, but possibly one which is
less forgiving. You decide how far you want to go.
Ira
Crummey
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