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).]
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.
Also a stock roll bar in the rear would mean the front rollbar would likely be too small if you didnt also upgrade that.
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.
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).]
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.
Oh I actually didn't know that. Thanks for the info
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.
Understandable. I will definitely keep up on this thread because I have an 87
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).]
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).]
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.
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.
The main reason that 84-87 Fieros have Bump-steer is because of a HUGE mistake in the suspension design; With a Strut suspension, the Tie-rod length should be based on the width of a triangle using the top point of the strut, and the ends of the lower arm. The lower arm of the 85-87 Fieros is approx' 12.5 inches, and the tie-rod is ABOVE that arm, so it should (Obviously) be SHORTER than the lower arm- but, instead, it is 15 inches long.
I can even understand how the designer came up with this; He thought, "I don't want the tie-rod changing the toe of the rear wheels....I....um...hmmm- I'll just make it as long as possible and it won't hardly change length!" Yes, but that lower arm DOES change length, so the wheels are constantly turning in and out as the suspension compresses and extends.
The tie-rod should have been closer to 11 inches long- would have (Basically) eliminated that bump steer.
Quick diagram of this;
[This message has been edited by cvxjet (edited 12-14-2022).]
I don't think it is that simple since the steering arm is higher than the ball joint, and while the ball joint center moves in an arc, the steering arm path of travel is affected by the linear motion of the strut.
In addition, the axis that the control arm pivots about is not parallel to the centerline of the car, allowing the wheel to move backwards as the suspension compresses and forwards as it extends. The tie rod when viewed from above is angled in the opposite manner, which affects the relationship between how they both move.
There is also the relationship to toe change via bushing deflection as well as just compression and extension of the suspension.
I want to remove a bunch of these variables, I want to get rid of the sweeping backwards action of the rear control arm and make its pivoting axis parallel to the centerline of the car. I could make the tie rod end center the same height and distance as the ball joint and tie it to the control arm, but if I want to be able to dial in a little toe in under braking and accelerating forces, then flipping the knuckles left to right will give me more control of this behavior. I just need to keep reading to figure out whether it would be beneficial. Since the car is so prone to snap oversteering, some toe in to keep the rear of the car following the front may be beneficial, which is why I am exploring the idea of swapping knuckles side to side.
But by swapping knuckles side to side I can mess around with the characteristics depending on where I locate the toe links inner pivot. Move that pivot forwards and it toes out under acceleration and in under braking. Move it backwards and you get the opposite behavior. Move it down and you get toe in under compression and toe out during extension. Move it up and you get the opposite. Shorten the link and you get more exaggerated amounts of toe change. Make it the same length as control arm and you dial in 0 toe change (if toe pivot was at same height as ball joint). Would be cool to make it tunable to mess around with it.
[This message has been edited by zkhennings (edited 12-14-2022).]
I've had this tab on my browser for months to reply... I guess today's the day!
quote
Originally posted by zkhennings:
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.
There's not very much room at all to raise the rear LCA pivot without running into the coolant pipe. I did this by spacing the crossmember down from the tub, but that then requires some other method of lowering to get the rid height down where it was.
quote
Originally posted by zkhennings: 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.
Tilting the knuckle back to add caster raises the outer tie rod end, which alters bump steer.
quote
Originally posted by zkhennings: 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.
If you're going new cradle, you can rotate the control arm pivots around a vertical axis through the ball joint in order to get the inner pivots parallel to the centerline of the car. Raising the front pivot on the stock cradle requires fussy fabrication, but is probably more practical than lowering the rear pivot to reduce pro-squat.
quote
Originally posted by zkhennings: 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.
The in-plane toe link is the best possible solution, as long as the axis from the outer toe link pivot through the ball joint is parallel in plan view to the inner pivot axis of the control arm. The '84-'87 knuckles will not move the struts if they are swapped L/R. Custom knuckles could lower the outer ball joint to improve roll center, while reducing the need to move the inner pivots as much.
quote
Originally posted by zkhennings: 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.
You'd want to move the coil over down to act on the bottom of the knuckle so that it could be essentially inside the wheel. That would allow more wheel width at the inboard edge, since there wouldn't have to be clearance for a strut or shock going up.
quote
Originally posted by zkhennings:
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.
If you ran a lower offset knuckle and longer control arms, similar to an '88, the wheel offset requirements would be less extreme.
quote
Originally posted by zkhennings:
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.
Hardening all the pivots and going to a significantly wider rear tire helps tremendously. What are your current tire sizes?
The main reason that 84-87 Fieros have Bump-steer is because of a HUGE mistake in the suspension design; With a Strut suspension, the Tie-rod length should be based on the width of a triangle using the top point of the strut, and the ends of the lower arm. The lower arm of the 85-87 Fieros is approx' 12.5 inches, and the tie-rod is ABOVE that arm, so it should (Obviously) be SHORTER than the lower arm- but, instead, it is 15 inches long.
I can even understand how the designer came up with this; He thought, "I don't want the tie-rod changing the toe of the rear wheels....I....um...hmmm- I'll just make it as long as possible and it won't hardly change length!" Yes, but that lower arm DOES change length, so the wheels are constantly turning in and out as the suspension compresses and extends.
The tie-rod should have been closer to 11 inches long- would have (Basically) eliminated that bump steer.
Quick diagram of this;
For zero bump steer, the toe link has to point to the same front view instant center as the control arm and the perpendicular line from the top of the strut (which together define the instant center).
I am not a suspension expert by any stretch, but my 87GT suffered from bump steer when I first bought it. I replaced the rear struts with KYB units, the front shocks with Monroe (softer). added the ADDCO matching front, rear sway bars and replaced the cradle and suspension arm bushings with poly . The car now handles great and there is no bump steer. Can't say that I'm ready to road race but under all conditions the car holds the road very nicely.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
While all these discussions on suspension geometry are very interesting, in the real world we (or I) just tweak what we've got. My '87 handles a treat on track and I've never experienced bump steer. If I was to build a "real" race car, it wouldn't be with a Fiero because the damn thing is just too heavy. But for trackdays and having fun, it's great!
A long time ago, Alpine wanted to race with the big boys at Le Mans (24 hours). They had achieved mild success in smaller classes with a very good chassis and small engines. So they developped a nice V8 (twin cam 4 valve heads) and mated it to a modified and well built chassis. Look up the 1969 Alpine V8 and you can see it's a pretty car. The only problem; it was 100kg heavier than the equivalent Porsche race car! All the super suspension didn't do anything and the car wasn't competitive!
------------------ "Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France! @turboslugfiero https://youtu.be/c4Cu7_2OgYc
I am not a suspension expert by any stretch, but my 87GT suffered from bump steer when I first bought it. I replaced the rear struts with KYB units, the front shocks with Monroe (softer). added the ADDCO matching front, rear sway bars and replaced the cradle and suspension arm bushings with poly . The car now handles great and there is no bump steer. Can't say that I'm ready to road race but under all conditions the car holds the road very nicely.
The cradle moves around a lot on the old worn out cracked original bushings. The front and rear control arms move around a lot on their big gooey old crappy worn out bushings as well. That's not bump steer... it's just trash bushings.
