Welcome to my newly
redesigned Fiero 2M4 resource site. The original site recorded over
12000 visits, hopefully this one will also prove as useful.
Budget Street Handling:
Design for less Understeer: racers need not apply
1984-87 Suspension set up:
Most discussions on Fiero handling improvements focus on reducing understeer and dealing with bump steer in the rear suspension caused by the mounting points of the toe links in the rear suspension. * This discussion however will look at things from a different slant.
Understeer is a benign handling characteristic which can keep even the most inexperienced driver from getting into too much trouble. Cars with a rearward weight bias are especially tricky since they often display a condition called
trailing throttle oversteer. GM, by installing only a front anti-roll bar on the 1984-87 Fiero, dialled in lots of understeer. In stock form the Fiero is a very forgiving car since getting back on the throttle will usually bring the understeer back (unless you were going too fast to begin with). As we decrease the understeer, we increase the risk of trailing throttle oversteer, and more importantly, we make the oversteer more difficult to "catch". Before we start building an autocross car lets be honest about our real driving habits. Do we really need, or even want, a nervous competition ready car? Do you really want a car you are afraid to drive in the rain? If you are actually using your Fiero in the commuter car role which sold it to the GM brass does it require cutting edge handling, especially at the expense of daily livability?
Let's take a look at the elements of good street or real world handling:
1. Consistency, good street handling should have no surprises.
2. The ability to handle changes in road conditions.
3. A ride comfortable enough to live with for long drives.
4. Good high speed stability (especially in the highway speed ranges).
5. A confidence inspiring feel which makes you want to drive this car.
6. High levels of cornering power.
7. A forgiving nature which will not "bite you" for minor errors.
8. It has to please you not me, or anyone else.
Remember, what follows are suggestions of what "I" would do so you have to decide how much would apply to "you".
How can we achieve that in a Fiero? Lets take a look at what can be done on a reasonable budget.
STEP 1: Fix everything first. Shocks, struts, ball joints, rod ends, bushings, tires, brakes, if these parts are not in good order your handling will suffer. Adding new parts such as larger anti-roll bars, or making changes in alignment will be of no use if the car is not mechanically sound to begin with.
STEP 2: Firm up the suspension. As part of STEP 1 you may install stiffer aftermarket shocks and struts. Stiffer bushings for the rear control arms of 84-87 models will make a noticable difference in taming the trailing throttle oversteer (urethane may be all that is available, however if the correct bushings for the Citation X-11 of 1982-85 are still available they are three times stiffer than stock Fiero pieces with none of the drawbacks of urethane).
STEP 3: If the budget allows, a set of matched anti-roll bars. If you add a larger 1" front bar such as Addco's and then the 7/8" rear bar you will have a car which corners much flatter with less understeer (but still lots of understeer). (Also available from The Fiero Store.) Remember, my premise is that for comfortable street driving we want enough understeer to keep the car stable and protect you from the occasional episode of brain fade. We want a daily driver, not a racer. Be sure to use urethane in the sway bar mounts and end links, we want instant reactions from the bars. This single step will have the greatest effect on overall feel. Some suggest that, the steering damper can be removed affording a slight improvement in steering response and feel.
STEP 4: Tires. Here your budget is the limit. On stock 13" wheels you are somewhat limited, however there may still be some decent 205/70X13 available, 195/70X13 are slightly undersize but close enough to keep the speedometer reasonably accurate. Either of these is an improvement over the 185/80X13 rim protectors which were stock. On stock 14" wheels sizes from 185/75X14 to 215/60X14 fit without problems. Any wider could be pushing things on the 6" alloy rims (don't even think about it on the 5.5" steel wheels). As wheel size increases so do number of choices. The most important factor here is that tires with some performance potential be used. Beware of the hyperperformance Z-rated rubber, it sticks like glue but costs big bucks and does not wear well, only use them if your budget can handle it.
Placing wider tires on the rear has very little handling advantage (actually increases understeer at higher cornering loads), but it looks good so you choose, just keep the tire type the same and don't go too far apart on the sizing.
The most radical I have seen on stock wheel sizes was a strange mix, asymmetric H-rated 185/70X14 tires on Grand Am wheels (same pattern different offset) on the front, with 215/60X14 H-rated directional tires on Fiero wheels at the rear. The difference in the wheels reduced his steering kickback slightly (his claim) because of the greater offset. The Fiero wheels have a pronounced rim while the Grand Am wheels are relatively flat which further exaggerated the size difference. The only claim that I can make is that it drove fine at around town speeds and the narrower tires did reduce steering effort at low speeds.
STEP 5: Wheel alignment. Make sure it is at factory specs at least, this is satisfactory for most drivers. If you want to improve the response on the 1984-87 models try Slight negative camber front (0 to 1 degree) and rear (near 2 degrees). Rear must have at least some toe in (1/8", 1/16" at the front). Set the front for all of the caster it can give (achieved by moving spacers on the upper control arm mounts). If replacing the upper front ball joints slot the mounting holes to allow more camber adjustment, or get adjustable ball joints. This is not my area of expertise so look around for sites which publish alignment specs.
STEP 6: Now you have reached the limits of a relatively stock setup. Dipping a little into the more exotic solutions supplied by companies such as Ryane Motorsports we can tackle the bump steer issue with Ryane's fix, a new lower rear control arm which eliminates the toe links. This is costly but if you factor in the fact that this also eliminates four rod ends and replaces the control arm bushings, it may very well be a bargain. Herb Adams VSE has some suggestionsas well, Adams is an ex-GM engineer famous for the hot handling Firebirds of the 1970s and 80s .
STEP 7: Enjoy your car, I will stop here and leave the more radical work to the racers such as George Ryan.