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| Pre-88 Fiero Suspension Ideas (Page 1/2) |
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zkhennings
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DEC 12, 03:25 PM
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My current suspension is stock with all greaseable poly bushings, a stock front sway bar in the rear, aluminum cradle bushings, cut springs up front with 350# coils in the rear, and KYB struts and shocks. I also have the staggered 88GT wheels. The car handles decently (could probably pull some decent Gs) but it does not inspire driver confidence.
I have a basic plan for suspension modifications I would like to make to my 85 and I am looking for feedback. Most of these ideas are inspired by many suspension threads on here and over at RFT.
All of these ideas require custom control arms. I have dreams of fully redesigned sub frames and multilink suspensions with custom or upgraded knuckles and spindles, but this is more an exercise in the path of least resistance, as I want to drive this thing.
Front End:
Add anti-dive by raising rear mounting hole location. May require cutting into the chassis to make room for it to raise enough. Heim joints will help with this space grab and axial misalignment. Trying to reduce bumpsteer and positively affect roll center by not lowering front pivot. Custom lower control arms. Will allow for coilovers up front with the addition of an upper mount for the coilovers.
Add static caster and better roll center location with custom upper control arm by lowering inner mounting locations and moving the top of the knuckle to the rear of the car. Can be balanced out by moving the lower ball joint farther forwards with custom lower arm. Angle of upper arm (height of front vs rear pivots) can be used to help reduce additional bump steer and help anti-dive too.
Rear End:
Add Anti-squat by raising front pivot. Front pivot will have to be moved forwards enough to clear the transmission so that the pivot can be inboard enough to create an axis parallel to the vertical midplane of the car. Rearward tire movement on compression will be controlled by anti-squat angle. Side effect of wider mounting points is more resistance to braking and accelerating forces with downside of more unsprung weight due to larger control arm. Heim joints to be used.
Raise the roll center by raising both front and rear pivot points, but front moreso than rear for desired anti-squat.
Control bump steer and improve anti-squat by flipping rear knuckles left to right. Strut will be biased farther forwards which will require narrow coilovers to fit in strut tower. Mounting holes will need to be moved forwards, and I would move strut tops inwards as well to help with roll center. Bump steer and toe in general would be controlled better with a toe link that is perpendicular to control arm axis, and parallel to the ground at ride height. Mounting point can intersect axis or be shorter than whatever that length would be. With this concept all toe changes will be toe in regardless if suspension is compressing or extending, or deflecting from braking and accelerating. The idea would be to make the toe change as little as possible, but if it does change, it is never toeing out.
A solution similar to Yarmouthfiero and wtfb to create (theoretically) 0 toe change could be used as well, but I wonder if light toe in would not make the car more stable with such a short wheelbase. This direction for 0 toe would also increase unsprung weight.
Future plans would be for a beefy upper control arm that would have a mount for a coilover spring that would also mount to the strut tower. This would be for further improvement of dynamic roll center location.
In addition to these changes, running the correct tire stagger for weight distribution, and higher offset front wheels. I already have 88GT wheels on my Fiero and the higher offset front wheels made it behave a lot nicer. Spring rates and roll bar rates would also need to be optimized.
Overall this scheme would be pretty low effort all things considered, and relatively low cost. I am certain I am overlooking things so please help me develop my plans. I want the car to feel predictable, squat and dive less, attempt to make better use of the tires, and not need to be as stiff as my current setup has to be in order to "handle" well.[This message has been edited by zkhennings (edited 12-12-2022).]
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Xenoblast
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DEC 12, 04:12 PM
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I don't know that much about suspension but to me it seems like your front is undersprung. I have 300 pound (I think) 1.5 inch lowering springs in the front with the stock roll bar, and my front feels very planted. Also a stock roll bar in the rear would mean the front rollbar would likely be too small if you didnt also upgrade that.
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Patrick
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DEC 12, 05:11 PM
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| quote | Originally posted by Xenoblast:
Also a stock roll bar in the rear would mean the front rollbar would likely be too small if you didnt also upgrade that.
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Keep mind that there are some differences in size of the "stock" sway bars factory installed on '84-'87 Fieros. On my '84 that I autocrossed for years, I had a thinner "stock" sway bar mounted in the rear. I also made the front sway bar perform like a thicker bar by utilizing Rodney's Zero Lash End Links up front, while retaining the rubber bushings in the back end links. I swear my '84 (also lowered with cut springs all around) handled better than my '88 Formula did at autocross, it just didn't have the power I wanted/needed to exit the sweeps.
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zkhennings
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DEC 12, 05:11 PM
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While I am sure I could balance it out better, I went the path I did to try and tune out the inherent understeer that the car was designed with... but the overall geometries of the suspension leaves a lot to be desired. Making the suspension stiffer is only the answer to making it handle better because the geometries are less than ideal, and making it stiffer keeps the car closer to its static geometries. Ideally you only want to go as stiff as you need for the type of driving you are doing, it can be calculated with simple harmonic motion.
My car handles well as is and would be fine on a smooth track, but on real roads it leaves a lot to be desired, and an overly stiff suspension leads to less tire contact with the road if it is less than smooth. Never mind the lack of good shock and strut options to handle a much stiffer suspension.
Mainly I enjoy design and fab and want a challenge.[This message has been edited by zkhennings (edited 12-12-2022).]
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Xenoblast
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DEC 12, 05:17 PM
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| quote | Originally posted by Patrick:
Keep mind that there are some differences in size of the "stock" sway bars factory installed on '84-'87 Fieros. On my '84 that I autocrossed for years, I had a thinner "stock" sway bar mounted in the rear. I also made the front sway bar perform like a thicker bar by utilizing Rodney's Zero Lash End Links up front, while retaining the rubber bushings in the back end links. I swear my '84 (also lowered with cut springs all around) handled better than my '88 Formula did at autocross, it just didn't have the power I wanted/needed to exit the sweeps. |
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Oh I actually didn't know that. Thanks for the info
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Xenoblast
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DEC 12, 05:19 PM
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| quote | Originally posted by zkhennings:
While I am sure I could balance it out better, I went the path I did to try and tune out the inherent understeer that the car was designed with... but the overall geometries of the suspension leaves a lot to be desired. Making the suspension stiffer is only the answer to making it handle better because the geometries are less than ideal, and making it stiffer keeps the car closer to its static geometries. Ideally you only want to go as stiff as you need for the type of driving you are doing, it can be calculated with simple harmonic motion.
My car handles well as is and would be fine on a smooth track, but on real roads it leaves a lot to be desired, and an overly stiff suspension leads to less tire contact with the road if it is less than smooth. Never mind the lack of good shock and strut options to handle a much stiffer suspension.
Mainly I enjoy design and fab and want a challenge.
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Understandable. I will definitely keep up on this thread because I have an 87
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cvxjet
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DEC 12, 10:48 PM
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First off, I would suggest installing an 88 rear subframe/suspension- much-MUCH better design; Each arm (Basically) only does one thing so it can be perfected for that job...Plus the subframe is solid mounted which adds to the stiffness of the chassis.
Second, I had an idea for improving the front geometry of the 84-87 front suspension; Drill a hole through the frame just below the spring perch for a tube to mount the upper A-arm lower for better chamber-gain.....Basically, similar to the "Shelby mod" on old Mustangs. I believe you could do this and just use the coil of the spring to clear the tube.
Here is a pic of what I am suggesting;
 [This message has been edited by cvxjet (edited 12-12-2022).]
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zkhennings
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DEC 13, 11:36 AM
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Definitely, my plan is to see how much lower that inner pivot should be to optimize the geometry as best I can with what I have to work with. I also want to figure out the ideal angle it should be at (height of front pivot vs rear pivot) to compliment the anti-dive I will be adding via the lower arm. [This message has been edited by zkhennings (edited 12-13-2022).]
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lou_dias
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DEC 13, 09:41 PM
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The RCC kit added a 3.5 - 4 " offset spacer to the stock mounting point of the tie rod and used a shorter tie-rod that mounted to that. This allowed the tie-rod travel to more closely match the travel of the control arm.
This does a pretty good job reducing bump-steer.
My 1987 GT 4.9L 6-speed car has understeer with this mod.
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zkhennings
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DEC 14, 02:08 PM
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I seem to recall that while the RCC mod helped reduce rear bump steer during cornering levels of suspension deflection, but at the upper limits of travel like from hitting a large bump, it would actually bump steer more than stock. I live in the pothole capitol of the US (new england) so I really want more than a bandaid solution. Which would be either be to tie the toe link to the rear control arm for 0 toe change, or to put the toe link in front of the rear wheel center which seems like it would be way better positioned for controlling toe.
Having the toe link behind the center of the rear wheel seems like a recipe for unavoidable toe out bumpsteer in most situations of rear wheel deflection. It also seems much more prone to bending than if it was in front of the rear wheel center, also leading to toe out.
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