The next step toward creating baseline data for the stock Fiero rear suspension was to measure and draw out the actual suspension pieces. The 1988 Fiero suspension is an independent, three-link design comprised of two lateral links and one trailing link mounted to the bottom of the knuckle, and a Chapman strut to locate the top. The strut and trailing link are best shown in this side view, as well as the centre of gravity which is located 1020 mm ahead of the rear axle, and 495 mm above the ground:
The location of the center of Gravity (CofG) of the car in the vertical plane was taken from Road & Track Magazine, Sep 1983, in the article Pontiac Fiero Introduction from the Technical Analysis section. Although this was specifically for the '84 four cylinder car, I assumed the height of the CofG didn't change much, if at all with the introduction of the V6;
The horizontal location of the car's CofG was calculated based on the reported front to rear weight distribution (47%:53%) from various magazine sources testing cars with the V6, namely: Road & Track Oct 87, Automobile Magazine March '87, and Car & Driver Feb '86.
The top view best illustrates the two lateral links and shows how the trailing links converge toward the front of the chassis:
Lastly, the rear view completes the picture showing the angle of the Chapman struts, which play an important role in determining several suspension metrics:
The ride height of the car (ie ground clearance of the cradle) was a rather fuzzy measurement to take empirically given the variables (tire heights and spring sag to name two.) So I referred to the ’88 service manual but found problems there too. It gives the ride height in a table on page 3-16 but the accuracy of the numbers is contestable since the ride height doesn’t seem to change despite three different listed tires sizes. There is a 4.5 mm difference in the radius between the tallest tire (215/60/15) and the shortest tire (195/70/14) listed, yet the ride height remains the same according to the manual. I also referred to various magazine articles which stated the ground clearance as anywhere between 5.4” to 6.0”. In the end, I decided to let the ground clearance set itself by drawing the lower lateral links parallel to the ground, and adding the P215/60R/15 tires digitally onto the hubs. The dimensions for the installed tires came from two different sources averaged out: an actual ’88 GT with brand new Goodyear Eagle Triple Treads, and my own ’86 GT with 1500 miles on Goodyear Eagle ResponsEdge tires at 32 PSI. Final clearance = 6.25" (159 mm).
I was finally ready to start analyzing the behaviour of the stock 1988 Fiero rear suspension.