| Info - 84-87 models |
| Handling Info |
| Tuning |
"Does the 84-87 suspension identically match the Chevette/Citation or do they just share some components?"
I think they just share the basic design. The only front pieces I could find that are the same:
1984-87 Fiero KNUCKLE, steering LH 14001235 $148.00 1984-87 Fiero KNUCKLE, steering RH 14001236 $148.00 1976-84 Chevette KNUCKLE, steering LH 14001235 $109.00 1976-84 Chevette KNUCKLE, steering RH 14001236 $109.00 1984-87 Fiero BEARING, front wheel inner 9415132 N.L. 1984-87 Fiero BEARING, front wheel outer 9415135 N.L. 1976-84 Chevette BEARING, front wheel inner 9415132 $9.18 1976-84 Chevette BEARING, front wheel outer 9415135 $8.48
(Chevette prices from April 1984 book)
None of the rear Fiero parts are the same as the Citation front parts. I'm not saying they won't fit, just that the part numbers are different.
From: Scott Backer
Yes, not only have I driven several, but I have also measured and analyzed the geometry with a program (GeoScan) written to analyze the entire motion dynamics.
From a drivers perspective, there are two distinct problems:
Trailing throttle oversteer. This occurs when the car is on a turn such as exiting a freeway, and the driver lifts off the throttle. Two things happen here, (1) weight (not lateral inertia) is tranferred from the rear to the front, unloading the contact force of the rear tires. (2) Some suspension designs (84-87 Fiero rear) will "bump steer" or turn in relation to ride height. The outside rear tire on these Fieros turns outwards as it rises, at an average (its non-linear) of .06" per inch of extension (based a rolling tire diameter of 25"). This may not sound like much, but when you start looking at slip angles of tires (usually 15 D with street tires) and how close they are to the slip angle limits (again non linear) at .5 Gs of lateral force, you can really begin to appreciate how this minor toe out intensifies the cars physical desire to swap ends when decelleration in a turn occurs.
To compenate from the factory, they attempted to dial in plenty of understeer.
Its worth pointing out that this condition with the Fiero is far better than the early $60,000 Turbo 911s experienced. I can recall the late Al Holberts comments on the danger of racing the early models, so he shunned the free factory Porsche in exchange for a Chevy Monza at his own expense to race in the 1975 IMSA GT class.
Fatalitities in SCCA Showroom Stock racing are rare, but Bruce Dodge was killed in his 85 Fiero due to losing the car entering a turn, back in 88.
In 1988, the suspension was retrofitted with what was originally designed before the bean counters changed to what was used in the 84-87 models. The outside rear wheel now steers in about .04", not as a result of the height changes, but as a result of tranverse (forward-backward) loading. It was the Wiessech Axle objective of the 928 that spawned the design goal. The result nearly eliminates trailing throttle oversteer, and allows a far more neutral balance.
The bump steer can be fixed with some judiciuos cutting and welding to relocate the track rod, and after doing about 5 of them for people, it really makes a positive difference in handling.
The second problem is in the front end. Let me first point out that all 1988 Fieros have the mounting provisions for a power steering system on the rack, yet none of them where ever delivered with power steering. You could even buy the entire power steering kit from GM. Hmmm.
Scrub Radius. Look at the front tire, and drop an imaginary line from the center of the top of the tire to the center of the bottom. Lable this contact point on the ground, "Point A". Now run a line from the upper control arm ball joint center, to the lower control arm ball joint center and continue this line straight extending to the grond, and label it "Point B". The distance between Point A and Point B is called Scrub Radius, the distance of the moment arm where the tire literally scrubs through a turn.
What does Scrub Radius do? Several things.(Lee, Ill get to karts in a minute). First it adds friction to turning the wheel and reduces the mechanical advantage making it much harder to steer. (Now you can see why the power steering was planned for the 88 model year, as the system was developed before the resurrected suspension was re-evaluated). By adding more friction, it also attenuates some of the road feel, despite the greater leverage, or at least to a point where larger bumps will over come the friction, and with increasing larger bumps amplify the kickback to the wheel. It also adds to tire wear, and ball joint loading.
Kart dynamics have few different priorities. Using the frame as suspension, they actually benefit from large scrub radius numbers. With the castor dialed in to the spindles somewhat fixed, the load on the opposing corners (in an X) can be set by changing scrub radius. There is some compromise in the virtual swing axle center to contact center X axis dimension when changing scrub radius. (These formulas are used by Williams, Lola, Reynard, etc. and may not be the terms used in Karts).
In the end, given both are equipped with the WS6 option and same tires, I find it is far easier to drive a stock 88 model at 10/10s than it is to drive an 87 at 8/10s. I owned an 87 GT for a year.
An 84-87 model is still far better a sports car than anything with front wheel drive unless one compares the handling abilities in reverse.
Seven years of SCCA Sports 2000 and Formula Continental racing along with my 88 Formula has spoiled me indeed.
From: John Denman
Though I have not discussed changing the front bar, I agree with the other responses that you have received that it is a simple, direct change out. I also agree that you should NOT go to a stiffer front bar. The Fiero has a lot of understeer. It benefits greatly from the addition of a rear bar. A larger front bar will increase the understeer--not what you want!
There have been numerous comments from owners about how well the Fiero handles. Things that help create this impression are its relatively stiff springs, its low center of gravity, its relatively large tire footprint (with the 215/60-14s) and the low polar moment of inertia (mid-engine). Those who don't believe that they have a lot of understeer have probably not pushed the limits. Understeer is safe, and that is why manufacturers design it in. You can lift the throttle in the middle of the corner and the front end will tuck in. With enough understeer, there is little likelihood of spinning.
Those who have actually spun their cars have probably slowed in the middle of a turn. True understeer/oversteer is with the vehicle speed constant. Driver input from greater throttle, lifting the throttle, or braking will change the balance. An experienced driver can skillfully use these to help get the desired cornering from a vehicle, and on the track, it's done all the time. It's call car control. In fact, the Skip Barber Driving School has a Car Control Clinic, and it is a day spent mostly on an autocross course doing just this. By the way, if you are interested in that, I believe that the Three Day Competition Course is a prerequisite. I have been through both, and believe that if you really want to learn about fast driving, this is an excellent approach.
My purpose in explaining all this is to help clear up what is understeer and oversteer. Those who have spun on the street by entering a exit ramp way too fast and then slowing may tell others that the Fiero oversteers. This is simple a misunderstanding of the concept. I hope this helps to shed some light on the subject and not further muddy the waters!
From: Earl Zwickey
"My 84 SE has 215/60 14's all the way around, and understeers (pushes) too much for me. In my Nascar (game) manual, it recommends more in front and less in rear for understeering. Is this the same in reality?"
The same principles hold true on street cars, however you can only correct/make small changes to the handling by doing this, and you may/will experience increased tire wear. Note also that in typical street driving these changes may not really be noticable.
When you autocross a car, the "poor mans" method to adjust your tire pressures is usually accomplished by putting shoe polish on the edges/sidewalls of the tires and doing a practice race run. The run will scrub off the shoe polish where the tire contacts the ground, based on the marks left over, you can then adjust your tire pressures so that the desired/optimal amount of tread is in contact with the pavement. Typically if you decrease the pressure in the front (theoretically increasing the "bite" of the tire) and increase the rear, you are going to bring the cars handling more towards oversteering tendencies, and vice versa. Note that for optimal Autocrossing/Solo racing, certain vehicles may have very large differences in pressures from front to back that would make street use impractical. I successfully raced a Toyota MR2 that used to take about 20psi in front and 38 psi in back to achieve the slight oversteer that I wanted.
If you want to make larger changes to your cars handling, a sway bar is probably the best way. Adding a sway bar to the rear of the Fiero is a great, relatively inexpensive way to get more neutral handling; you can then adjust your tires for small changes. A sway bar will also not noticably affect the stock ride quality of your vehicle.
Just to add to the debate/confusion, running different size tires from front to back can also be used to tune the handling. Its really tough to rotate tires though! :)
From: Eric Gutknecht
