Suspension changes I made to my 86 duke

During the meeting it was suggested that I should list what I've done to the car for autocross. So here's what I've done, I'll try to keep this as brief as possible but I want to also justify why I've made some of these changes.

Before I start, I should say that if you're at all interested in autocross, come out to an event first to try it out before playing with your car. So long as it's not falling apart or going to fall apart, and your battery is bolted down securely you can come out and have fun. And that the biggest variables are the driver and the tires you're using, not the suspension. Though, a properly set up suspension can make the car easier to drive fast and more enjoyable.

Quick summary:
Fresh Bushings, added rear sway bar, KYB shocks and struts, better tires, better alignment.


Replaced worn out bushings with new rubber ones:
I figured poly would be too uncomfortable on a daily driver, and fresh rubber would still be much stiffer than the old stuff.

Replaced shocks and struts with KYBs:
At the time I didn't realize I would be autocrossing so I went with KYB. Even still, I doubt the Konis be much help with the stock springs, but since I've never tried them out I don't know for sure.

Replaced all the rubber bushings for the sway bars with poly and added a rear bar:
Understeer is no fun. I don't know the sizes of the bars off the top of my head, but the front is the stock 86 one and the rear is whatever the Fiero Store sells.

Better tires:
This is the most important upgrade you can make to the car. I went with 195/60R14 Falken RT-615Ks (200 treadwear) as a compromise as something I could use in wet weather and for a small amount of driving around town. If you really want to go fast you'll need something stickier.

And finally, a more aggressive alignment:

The front of most Fieros seem to have either close to 0 degrees of camber or positive camber. When the car is cornering, one of the goals is to get the wheel as perpendicular to the ground as possible, so as much negative camber as you can get is important. I think I ended up with -0.5 deg. as the most I could get from the front. For the rear I ended up with about -1.5 degrees of camber. For toe, I settled on about 0 at the front and somewhere between 1/16" and 1/8" toed in in the rear.

Then at the front there's also caster to consider. There's washers at the top of the upper control arm which you move around to adjust it. With caster one of the things it does is the more you turn the steering wheel, the more the wheels will be tilted. So more positive caster will help the front wheels stay closer to perpendicular to the road as your cornering. The downside to this change is increased steering effort. Not sure what I ended up with on my car as I never measured it.


Since I've now driven my stock 88 Formula at autocross I can say these changes made the duke handle fairly well, maybe even better than my stock 88 (which has KYBs shocks and struts, stock height, and all the worn out bushings still). Though it could also be that I was more comfortable with it and need to learn how to adjust to the new car.

I came across this rather fine write-up tonight that I thought might compliment Colby's thread.

Improving Fiero Handling

Good stuff in there, some of which is surprising.

 

Cheese wrote: Patrick, there's a link to that article in Brian's topic from last year, "Performance Driving Resource Sites".

I thought possibly it had been mentioned previously, but I wasn't going to try hunting it down... and it's probably good enough to mention a second time anyway.

 

I'd just like to re-inforce the point I made in the other thread about this, but Colby's geometry suggestions are spot on. Seriously, in an autocross setting, you cannot get a decent sports tire to sit any flatter. Perhaps with a 100% slick an extra -0.1 camber at both sides could help, but none of us have those, so I'm not going to bother booting up the sim.