In my last post I forgot to add the cross section of the IFG front fender showing just how much the fibreglass fender is ill-suited for the car without major modifications. Here's the rear view drawing of the stock suspension once more with the IFG fender and some key measurements added in red:
A 148 mm vertical gap between the fender lip and the top of the tire is a whopping 5.8"! My challenge was to find a way to reduce this to an acceptable size and move the wheels outboard by about 76 mm each, without compromising the suspension's performance.
The most common way to lower a Fiero is to cut down the front springs, but even then, the maximum drop achievable is 50 mm which would still leave a 96 mm fender to tire gap. Chopped springs have a negative impact on the geometry and travel of the suspension though, and the remaining 96 mm gap would still be far from appearing Ferrari-like.
To address the inset wheels, the inexpensive route is to use wheel spacers or heavily offset rims, but both solutions would nearly triple the scrub radius causing problems with steering effort, kickback, bearing stress, and tire scrub. Needless to say cut springs and huge spacers weren't going to cut it for me.
Creating a new suspension is best done from the tires up, so that's where I started. I've already covered my rationale for tire selection back in post #51 so I won't go over it again here. As for front wheel selection, the main characteristic I was looking for (aside from the bolt pattern and width) was to maintain or reduce the stock scrub radius. I did it by choosing a 7" wide rim with a 48 mm offset.
That resulted in an inward movement of the wheel centreline by 11 mm as compared to the stock 6" wide wheels with a 37 mm offset. Here's the diagram showing the result (the red lines and text represent changes from the previous drawing):
In addition to the rim selection, adding the Corvette rotors moved the wheels a further 1.4 mm inboard since the rotor hat is thinner than the stock Fiero's rotor.
The combined effect of the wheels and rotors resulted in a decrease from the stock 40 mm scrub radius by 12.4 mm to 27.6 mm as shown above. That's an impressive and desirable 31% reduction. It also decreased the track width by 12.4 mm too.
The other notable effect that changing wheels and tires had was to raise the chassis by 12 mm. The stiffer sidewall of the new low profile tire compresses considerably less than the stock 60 series tire, despite its overall unloaded diameter being nearly identical. This of course raised the ground clearance and the centre of gravity, neither of which are desirable changes.
The next change I made on paper was to lengthen the upper and lower control arms by 76 mms, moving the outboard edge of the tire out to a respectable location:
These red arms are drawings of the former HT Motorsports (now Arraut Motorsports) extended-track tubular arms. They moved the street-side face of the tire so it now sits 13 mm further out than the top of the fender lip. It sounds like they might stick out a bit too much, but the fenders flare considerably wider towards the rear so I judged that this would strike a balance between too far in and too far out. The fibreglass fender can always be modified later.
The other notable point on the above drawing is that the ground clearance was reduced to 130 mm due to the lower control arm's low slung coil-over shock mount.
Here's a photo comparing the stock stamped steel control arms with the extended tubular arms:
These still didn't do anything to address the 148 mm wallowing gap between the top of the tire and the lower edge of the fender lip. Even though I knew I wouldn't use drop springs, I went ahead and had the data fed through the simulation software as though 50 mm cut springs were installed. The biggest effects were dynamic toe gain, anti-dive loss, an increase in roll moment, and a huge increase in roll centre migration during roll.
These results reinforced my decision to spend the extra money and buy drop spindles instead, which don't appreciably change the suspension geometry. Again, I went to HT Motorsports and bought their 1.5" (38 mm) drop spindles. I would have purchased 2" drops had they been available at the time. Here's a couple photos showing the drop spindles from different angles:
The nicest thing about these lowered spindles is that they do away with the obsolete and unobtainable '88 Fiero front wheel bearing assemblies and replace them with the very inexpensive and plentiful rear bearing assemblies. A large bolt is used as a replacement for the rear axle which normally holds the two halves together:
Assembled, they look like this, compared to stock:
I added the drop spindles to my drawings and lowered the suspension a further 12 mm by dialling the coil over shocks a bit shorter. Here's the impact of having done so, with the red lines showing the difference from the last drawing:
Most obviously the tire top to fender lip gap reduced by 51 mm to 97 mm, as did the centre of gravity from 507 mm to 456 mm. There was also a 4.6 mm increase to the half-track width because the new drop spindles are slightly wider than the stock knuckles they replaced. That too had a negative impact on the scrub radius bringing it up from 27.6 mm to 32.2 mm... still a respectable 19.5% reduction over stock.
Finally, to address the last of the wheel gap issue, I simply cut down the height of the mounting flange on the fibreglass fender... well, I did it digitally, at least.
I haven't done this mod yet and realize a change this simple isn't likely possible without requiring further reshaping of the fender. But at least at this point I knew the kit was salvageable.
Next up: What did these modifications do to the performance?