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Redesign a Fiero suspension for better geometry (Solidworks, ProEngineer, etc) by Austrian Import
Started on: 06-30-2011 06:13 PM
Replies: 382 (26968 views)
Last post by: zkhennings on 03-05-2014 04:56 PM
Austrian Import
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06-30-2011 06:13 PM Click Here to See the Profile for Austrian ImportClick Here to Email Austrian ImportSend a Private Message to Austrian ImportEdit/Delete MessageReply w/QuoteDirect Link to This Post

We all know that the '88 Fiero suspension is (arguably) better. But it's still 20 years old.

I always wondered if with modern CAD/CAM software it would be possible to design a more modern
A ) Double wishbone front + Double wishbone rear
B ) Double wishbone front + fancy multi-link rear
C ) another option I hadn't considered.

It would be great if it were to (almost) bolt in to the vehicle. Maybe use factory rear cradle attachment points and replace the rear cradle. The front end may be replaced as well, while utilizing the attachment points.

The goal is to apply what engineers have learned about suspension design in the last 30 years since the Fiero was built.

Let's put considerations such as: feasibility of actually making it a real life product, costs/reward, starting over with a tube-frame chassis, etc. on the back burner to let creativity flow.

Reasons I thought it would be a great idea to do this:
1) It is a great way to learn/share ideas about modern suspension theory
2) Learn suspension design applied to a specific project (with applied constraints), rather than just complete theory, or a scratch build vehicle.
2) hopefully get a good debate going (please without name calling, etc. let's keep this civil)
3) See how open source/collaborative thinking would work out in the Fiero world
4) provide an avenue to share technical information/content for people with similar interests.

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06-30-2011 06:28 PM Click Here to See the Profile for Austrian ImportClick Here to Email Austrian ImportSend a Private Message to Austrian ImportEdit/Delete MessageReply w/QuoteDirect Link to This Post

A couple great ideas from existing threads to get the ball rolling:

 
quote
Originally posted by 88lambo: in http://www.fiero.nl/forum/F...2/HTML/107913-5.html

Update...

Picking away at the cradle and the Fiero chassis, I got the fire wall stripped of all the brackets getting ready to cut the rear section off and start on building the tube frame from the firewall back.
I put the cradle into the chassis to see how it lined up, if you look at the photo from the back straight on you can see the center vertical tube are the same distance from the Fiero frame (which will be gone soon)
Tranny coming off engine this weekend then off to be rebuilt...

I guess since I will be cutting most of the rear section away I couldn't really call this a "Stock" engine compartment any more...so if you wanted to put this into a Stock Fiero I would retain the rear frame section (trunk still has to go) make the cradle suspension mounting points to use the fiero suspension components. You could use my lower suspension arms in conjunction with the Fiero rear shocks (or a coilover kit) and the stock shock tower...I still believe if you wanted to you could stuff this setup into a Fiero...which would be cool...Maybe my next project, a Fiero with the BMW V12 twin turbo!!!!













 
quote
Originally posted by ccfiero350: in http://www.fiero.nl/forum/F...3/HTML/000094-9.html


Here are some side by side images.

The new front end is about 30lbs heavier then the original one.


Most of it is in the new brakes.


They are just frigging big.


I can't wait to see how HHP's adjustable bars work out on the track.


The front sway bar on the old front end is an Addco bar that's 1.25" thick.


I have to admit with the mods done to the front sheet metal for the flip front end it made working on it much easier.


I balanced it on the floor jack and just lifted up in place in one piece.


1st trick is get the rear tab under the chassis mount pad. 2nd trick is get the alignment pin on the drivers side in it's hole.


Once you get the pin in, the rest of the bolts pull it pretty much into alignment.

[This message has been edited by Austrian Import (edited 06-30-2011).]

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Austrian Import
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06-30-2011 06:31 PM Click Here to See the Profile for Austrian ImportClick Here to Email Austrian ImportSend a Private Message to Austrian ImportEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by ccfiero350:

It been a while since I have posted here but work has been on going. I have been working with coppertop_01 designing some new suspension pieces.


There rear knuckle for an 88 is a unique piece, and limits the use of larger unitized bearing hubs. So I designed a new one that uses a Saturn Vue hubs and axle.


To fit my IMSA wide body, I need a least a 10 1/2" wheel, and cheap wide wheels come on mustangs. I also incorporated C4 disc with calipers mit parking brakes.


So my special thanks to bloozeberry for his subframe prints, I made a full math model of the 88 rear suspension.


This version features some changes in geometry to help with roll center, camber gain and anti squat with the 2" lowering.


I can do motion analysis with the software with animations, make changes and run it again. Really fun stuff.


I've got some mods to the sub frame that will re-locate the links a tad to fine tune the roll center.


 
quote
Originally posted by ccfiero350:

I did some motion analysis on the new knuckle and made some quickie low rez animations.


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Austrian Import
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06-30-2011 06:34 PM Click Here to See the Profile for Austrian ImportClick Here to Email Austrian ImportSend a Private Message to Austrian ImportEdit/Delete MessageReply w/QuoteDirect Link to This Post

One approach would be to add SLA's to the rear of the Fiero.

 
quote
Originally posted by Austrian Import:

Agent 47





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06-30-2011 06:41 PM Click Here to See the Profile for Austrian ImportClick Here to Email Austrian ImportSend a Private Message to Austrian ImportEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by Austrian Import:

The other idea I had was to mimic (or buy at $300-$600) a Porsche Boxster rear suspension:






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06-30-2011 06:53 PM Click Here to See the Profile for Austrian ImportClick Here to Email Austrian ImportSend a Private Message to Austrian ImportEdit/Delete MessageReply w/QuoteDirect Link to This Post

Coppertop's scratch built '88 engine cradle shows part of what I envision in this thread:









http://coppertopautosports....dle-fabrication.html
http://coppertopautosports....-fabrication_06.html
http://coppertopautosports....-fabrication_10.html

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sspeedstreet
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07-01-2011 01:20 PM Click Here to See the Profile for sspeedstreetClick Here to Email sspeedstreetSend a Private Message to sspeedstreetEdit/Delete MessageReply w/QuoteDirect Link to This Post

I've been thinking of the same things. I was looking at the Mustang SLA setup as well. The Fiero design wouldn't need the ball joints, but would need the strut pickup on the upright moved to clear the axle. To the side or my choice:



This animation shows a rocker type strut instead of the stock Fiero position, but you get the idea:


(Credit to dave@team321.com)

[This message has been edited by sspeedstreet (edited 07-01-2011).]

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07-01-2011 02:07 PM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by sspeedstreet:

The Fiero design wouldn't need the ball joints...


Enlighten me please. I'm not sure what you mean by this, but if you're suggesting that the upper control arm could be solid mounted to the knuckle, you wouldn't be able to control dynamic camber changes. On the other hand, if you meant that you could have a simple fulcrum at the top of the knuckle (like the lower lateral links on an '88) then you wouldn't be able to effect dynamic toe changes:

1. without soft fulcrum bushings, which would allow undesirable deflection of the arms in all axis, or;
2. without binding the upper and lower fulcrum bushings if using hard bushings, nor would it be very easy to adjust static toe.

The most versatile way to connect the knuckle to the control arms would be with ball joints, unless I'm over-looking something. If you're going to redesign the entire rear end, then it wouldn't make much sense to limit adjustablility unnecessarily.

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07-01-2011 04:35 PM Click Here to See the Profile for sspeedstreetClick Here to Email sspeedstreetSend a Private Message to sspeedstreetEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by Bloozberry:


Enlighten me please. I'm not sure what you mean by this, but if you're suggesting that the upper control arm could be solid mounted to the knuckle, you wouldn't be able to control dynamic camber changes. On the other hand, if you meant that you could have a simple fulcrum at the top of the knuckle (like the lower lateral links on an '88) then you wouldn't be able to effect dynamic toe changes:

1. without soft fulcrum bushings, which would allow undesirable deflection of the arms in all axis, or;
2. without binding the upper and lower fulcrum bushings if using hard bushings, nor would it be very easy to adjust static toe.

The most versatile way to connect the knuckle to the control arms would be with ball joints, unless I'm over-looking something. If you're going to redesign the entire rear end, then it wouldn't make much sense to limit adjustablility unnecessarily.


Obviously the lower ball joint is unnecessary on the 1988 design. The upper could be a spherical bearing. My point was there is no need to use the complexity of ball joints as there is no steering involved.

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ccfiero350
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07-01-2011 05:29 PM Click Here to See the Profile for ccfiero350Click Here to Email ccfiero350Send a Private Message to ccfiero350Edit/Delete MessageReply w/QuoteDirect Link to This Post

Just my 2 cents worth, a spherical bearing, rod end, heim joint, what have you, technically has the same freedom of axis movement as a ball joint, but have to limit their off axis movement to keep the bearing in the cup.

A real good reason to keep with ball joints is that they are easer to seal up and kept lubed. But their not as sexy as heim joint

------------------
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07-01-2011 05:52 PM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by sspeedstreet:

The upper could be a spherical bearing. My point was there is no need to use the complexity of ball joints as there is no steering involved.


Two counter points:

1. Good rear suspension systems are designed to "steer" using the change in the geometry of the control arms as they rise or fall in jounce and rebound to effect it; and

2. As ccfiero stated, a spherical bearing (heim joint, etc) is just another form of a ball joint.

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07-01-2011 07:36 PM Click Here to See the Profile for sspeedstreetClick Here to Email sspeedstreetSend a Private Message to sspeedstreetEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by Bloozberry:


Two counter points:

1. Good rear suspension systems are designed to "steer" using the change in the geometry of the control arms as they rise or fall in jounce and rebound to effect it; and

2. As ccfiero stated, a spherical bearing (heim joint, etc) is just another form of a ball joint.


Minutia. This is not a rear steer application; toe changes due to suspension movement wouldn't be more than a couple of degrees. You need a ball joint for that?

Really, a ball joint is a type of spherical bearing? A Ferrari and a Prius are both automobiles, but their benefits are not interchangeable. I proposed eliminating the upper ball joint shown in the Mustang front SLR pictured above to free up that point as a strut mount.

Now, do you have anything constructive to add to the discussion or do you wish to continue with the critique?

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07-01-2011 08:35 PM Click Here to See the Profile for ccfiero350Click Here to Email ccfiero350Send a Private Message to ccfiero350Edit/Delete MessageReply w/QuoteDirect Link to This Post

Minutia! What do you think suspension design is all about? We change our rear toe settings by 0.1 degrees and see measurable track time differences..

It IS about rear steering because it's built in the 88s. Why do you think the front horizontal link is shorter then the rear?

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07-01-2011 08:50 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by Bloozberry:
1. Good rear suspension systems are designed to "steer" using the change in the geometry of the control arms as they rise or fall in jounce and rebound to effect it; and


I don't think I'd go that far...
That's like saying that you always want the front bar bigger than the rear... The real answer is "that depends on everything else".

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07-01-2011 08:55 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by ccfiero350:

It IS about rear steering because it's built in the 88s. Why do you think the front horizontal link is shorter then the rear?



Umm... so what? Was that done for handling or packaging? How does that change the toe in bump? Droop? How does that change the toe in different conditions of bushing loading? If you're replacing the bushings with hard pivots, do you think the suspension still works the same way?
(Hint: I already know the answers; you don't need to lecture me...)
How does the '88 setup compare to equal length lateral/toe links, with the inner pivot of the rear link higher than the inner pivot of the front link?

FYI for everyone: The "oversteer moment" of a car is dependent on something like the FOURTH power of the rear toe angle. This means that tiny changes in rear toe have large effects in vehicle stability and "path accuracy".

In other words, your super trick geometry may produce a 0.1% effect, but that effect can easily be lost in the noise created by that last bushing you haven't replaced yet... or even if some component (like the cradle side rail, maybe?) isn't as stiff as you think it is.

Suspension design is more about not making gross mistakes than it is about getting everything excruciatingly perfect.

[This message has been edited by Will (edited 07-01-2011).]

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07-01-2011 09:51 PM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by sspeedstreet:

Minutia. This is not a rear steer application; toe changes due to suspension movement wouldn't be more than a couple of degrees. You need a ball joint for that?


I've already answered this question. It depends on how you plan to attach the strut and upper control arm to the knuckle.

 
quote
Originally posted by sspeedstreet:

Really, a ball joint is a type of spherical bearing?


Yes. Really. Ball = Spherical, Joint = Bearing in this case.

 
quote
Originally posted by sspeedstreet:

A Ferrari and a Prius are both automobiles, but their benefits are not interchangeable.


What does this mean?

 
quote
Originally posted by sspeedstreet:

I proposed eliminating the upper ball joint shown in the Mustang front SLR pictured above to free up that point as a strut mount.


Round and round we go. Again, exactly how would you attach the bottom of the strut to the knuckle, and to what and how would you attach the upper control arm?

 
quote
Originally posted by sspeedstreet:

Now, do you have anything constructive to add to the discussion or do you wish to continue with the critique?


Where'd that come from? I'm trying to understand what your proposal is.

 
quote
Originally posted by Will:

Suspension design is more about not making gross mistakes than it is about getting everything excruciatingly perfect.


 
quote
Originally posted by Will:

The "oversteer moment" of a car is dependent on something like the FOURTH power of the rear toe angle. This means that tiny changes in rear toe have large effects in vehicle stability and "path accuracy".


So which is it? Lecture us.

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gusshotrod
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07-02-2011 03:41 AM Click Here to See the Profile for gusshotrodClick Here to Email gusshotrodSend a Private Message to gusshotrodEdit/Delete MessageReply w/QuoteDirect Link to This Post

Rear roll steer is rear bump steer if it is designed into the suspension linkages. For roll steer to be independent from bump steer, it should be designed into the compliance of the linkage mounts, so that it is turned on by lateral loads, not vertical loads.

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07-02-2011 07:55 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by Bloozberry:

So which is it? Lecture us.


Gross mistake = keeping the same component relationships in the rear of a Fiero as in the front of a Citation.

Tiny unintended toe changes can be greatly reduced with hard pivots.

 
quote
Originally posted by gusshotrod:

Rear roll steer is rear bump steer if it is designed into the suspension linkages. For roll steer to be independent from bump steer, it should be designed into the compliance of the linkage mounts, so that it is turned on by lateral loads, not vertical loads.


Do race cars never want roll steer?

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07-02-2011 12:32 PM Click Here to See the Profile for gusshotrodClick Here to Email gusshotrodSend a Private Message to gusshotrodEdit/Delete MessageReply w/QuoteDirect Link to This Post

Like you said Will, it depends on everything else. Active rear steer (which would be very useful) is not allowed in any form of racing that I am aware of. Passive rear steer is not used in drag racing. In circle track it is used, but mostly to make up for lack of available tire stagger. In road racing or on the street it is useless in high horsepower cars. For lower HP cars it can be useful IF you can divorce the bump steer from the roll steer AND if the rear tires end up with more slip angle than the front suspension. The rear suspension has no need to be better than the front, as you will never be able to use the improvement. I doubt if anybody drives on the street close enough to the limit to make rear steer worthwhile. It would be much more useful to limit toe change as much as possible to improve stability.

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07-02-2011 12:50 PM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by gusshotrod:

For lower HP cars it can be useful IF you can divorce the bump steer from the roll steer AND if the rear tires end up with more slip angle than the front suspension. It would be much more useful to limit toe change as much as possible to improve stability.


I'm not saying this isn't so, but I am curious to know what you think the rationale was behind the GM engineers decision to have unequal length lateral links on the '88 rear when they started with a wholesale redesign of the cradle and suspension. It certainly wasn't because of packaging constraints. The only purpose I can see for it is to provide dynamic toe change, which seems to be a contrary point of view from what you've stated as the ideal.

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07-02-2011 01:24 PM Click Here to See the Profile for gusshotrodClick Here to Email gusshotrodSend a Private Message to gusshotrodEdit/Delete MessageReply w/QuoteDirect Link to This Post

One reason could be to limit toe out under acceleration, another could be that it would be safer for the average driver to design in some roll understeer.

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07-02-2011 03:35 PM Click Here to See the Profile for sspeedstreetClick Here to Email sspeedstreetSend a Private Message to sspeedstreetEdit/Delete MessageReply w/QuoteDirect Link to This Post

This is why this forum wears me down sometimes. An idea is proposed for discussion and immediately people jump in with minutiae. As in details that are of no consequence at the point of discussing the feasibility of an idea. Is an SLA design possible for the rear of a Fiero? Is it worth the effort? Is there sufficient strength in the stock wheel-well to support the UCA mounting points or will it need a subframe designed? Is there room enough for links of sufficient length on the passenger side even if you built a subframe? I don't know about your cars, but mine has an alternator pulley up against the inside of the wheel-well.

SLA systems exist. Bearings, bushings, ball joints, anti-squat, roll-steer . . . these are all things that can be designed in or out any way you want. They are not relevant (to me, anyway) at this point.

As for my comment "Really, a ball joint is a type of spherical bearing? A Ferrari and a Prius are both automobiles, but their benefits are not interchangeable.". There needs to be a sarcasm font. Of course I know a ball joint is a type of spherical bearing, but they each have there own application.

I guess I just hate to be lectured to.

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07-02-2011 03:50 PM Click Here to See the Profile for gusshotrodClick Here to Email gusshotrodSend a Private Message to gusshotrodEdit/Delete MessageReply w/QuoteDirect Link to This Post

Can it be done? Yes. Worth the effort? That is entirely up to you. This is a hobby. Enjoy yourself.

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07-02-2011 05:29 PM Click Here to See the Profile for kennnClick Here to Email kennnSend a Private Message to kennnEdit/Delete MessageReply w/QuoteDirect Link to This Post

Interesting discussion, and a nice front suspension mod by ccfiero. I have wondered if one could utilize the rear strut knuckle and lower suspension as is. Then, to the top of the knuckle, add a metal piece that would clasp the top of the knuckle, bolting through it in two places, that would have provision to receive a ball joint from an upper suspension arm with appropriate anti-dive angle. The principal advantage would be more ideal camber change geometry than the strut type geometry.

Ken

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07-02-2011 07:01 PM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post

That is essentially what sspeedstreet posted in his first picture. It is an interesting idea.

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07-03-2011 12:10 AM Click Here to See the Profile for wftbClick Here to Email wftbSend a Private Message to wftbEdit/Delete MessageReply w/QuoteDirect Link to This Post

i really want to do a double A arm rear suspension on the rear of my 86 fiero .and i have posted in other threads about this .and most supercars use this type of suspension .but in this months car and driver there is a 911 vs boxter handling comparo and the 911 wins and it uses struts all around .so who knows? maybe just more tweaking is what we need instead of wholesale changes .and Will , name me a car that has a bigger roll bar in the back .

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07-03-2011 12:43 AM Click Here to See the Profile for gusshotrodClick Here to Email gusshotrodSend a Private Message to gusshotrodEdit/Delete MessageReply w/QuoteDirect Link to This Post

Bigger roll bar in the back? Yenko Corvair. (After checking, they were the same size front and rear).

[This message has been edited by gusshotrod (edited 07-03-2011).]

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Will
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07-03-2011 08:52 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by wftb:

Will , name me a car that has a bigger roll bar in the back .


Herb Adams recommended setting a Fiero up this way. Some people in the community have had success autocrossing/racing cars set up like that. I don't agree with Herb, but he was able to make the car fast that way.


 
quote
Originally posted by gusshotrod:

Like you said Will, it depends on everything else. Active rear steer (which would be very useful) is not allowed in any form of racing that I am aware of. Passive rear steer is not used in drag racing. In circle track it is used, but mostly to make up for lack of available tire stagger. In road racing or on the street it is useless in high horsepower cars. For lower HP cars it can be useful IF you can divorce the bump steer from the roll steer AND if the rear tires end up with more slip angle than the front suspension. The rear suspension has no need to be better than the front, as you will never be able to use the improvement. I doubt if anybody drives on the street close enough to the limit to make rear steer worthwhile. It would be much more useful to limit toe change as much as possible to improve stability.


Several of the '90's Japanese supercars (FD3S RX-7, Z32 300ZX, 3000GT VR4, R32/3/4 Skyline GTR) had active rear steering systems. Modern enthusiast frequently eliminate these systems. If there were an unequivocal benefit, I expect they'd be kept.

I'm not much of a fan of roll steer and other "passive" ways of making a car "safe". If you exercise all of your options for building understeer into a suspension design, what do you think the end result will be? Understeer. You can then tune out the understeer, but the result would be a Jekyll/Hyde driving characteristic in which the tuning and natural tendencies of the chassis are fighting each other.
That same situation was built into the 84-87 Fieros in reverse. Being a rear-heavy car with equal tire fitment, the car naturally wants to oversteer. To make it "safe", GM tuned it for understeer. The result is that it understeers to the limit and then rapidly transitions to oversteer, has a vicious list-throttle reaction and generally can't be driven hard with confidence.

I'd rather build the car from the get-go to be neutral and transparent.


 
quote
Originally posted by gusshotrod:

Bigger roll bar in the back? Yenko Corvair. (After checking, they were the same size front and rear).



I've driven a couple of Corvairs. I like them. They can be setup to be absolute weapons on an autocross course. If the cooling fan drive belt weren't so gimmicky, they'd be serious cars.

 
quote
Originally posted by sspeedstreet:

Is an SLA design possible for the rear of a Fiero? Is it worth the effort? Is there sufficient strength in the stock wheel-well to support the UCA mounting points or will it need a subframe designed? Is there room enough for links of sufficient length on the passenger side even if you built a subframe?

SLA systems exist. Bearings, bushings, ball joints, anti-squat, roll-steer . . . these are all things that can be designed in or out any way you want. They are not relevant (to me, anyway) at this point.


Questions like "can it be done?" are trivial. Of course it can be done. There are thousands of 10 and even 9 second door slammers around the country that are back-halved, caged, etc. yet still driveable on public streets. There's FAR more work involved in building one of those cars than in 99% of Fieros that hit the track.
There's no reason the same couldn't be done to a Fiero: chop off everything behind the firewall and start from scratch to build an entirely new tube frame and rear suspension. The only thing you'd keep would be the stock body panel mounting points.

Unfortunately, when most people think of that kind of work on a Fiero, they think "Lamborghini" instead of "track monster".

[This message has been edited by Will (edited 07-03-2011).]

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ccfiero350
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07-03-2011 09:09 AM Click Here to See the Profile for ccfiero350Click Here to Email ccfiero350Send a Private Message to ccfiero350Edit/Delete MessageReply w/QuoteDirect Link to This Post

Porsche really does strut type suspensions better then anybody. They have been at it a while.

I did an x-cross once in the fiero with an ADCO rear bar and the stock front bar and found that it was much more eager to turn in, almost tail happy.

I do think it's possible to do a SLA rear, the real head scratcher will be the upper A-arm mounting base like others have said. The lower rear frame horn in that area would not take too kindly to that kind of side load.

But, it being a rear end after all, the real goal is better camber gain, just a little, a couple of degrees worth.

I would take advantage of the structure of the upper strut mount area and mount my upper A-arm there and make an adapter for my knuckle to place the BALL JOINT above and outside the wheel. It would require a strut bar to keep things in check, but it's now its in an easer area to deal with. The strut will need to be de-coupled from the knuckle by a clevis type of connection. This is a pretty common modern type of strut application.


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Will
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07-03-2011 09:25 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by ccfiero350:

Porsche really does strut type suspensions better then anybody. They have been at it a while.

I did an x-cross once in the fiero with an ADCO rear bar and the stock front bar and found that it was much more eager to turn in, almost tail happy.

I do think it's possible to do a SLA rear, the real head scratcher will be the upper A-arm mounting base like others have said. The lower rear frame horn in that area would not take too kindly to that kind of side load.

But, it being a rear end after all, the real goal is better camber gain, just a little, a couple of degrees worth.

I would take advantage of the structure of the upper strut mount area and mount my upper A-arm there and make an adapter for my knuckle to place the BALL JOINT above and outside the wheel. It would require a strut bar to keep things in check, but it's now its in an easer area to deal with. The strut will need to be de-coupled from the knuckle by a clevis type of connection. This is a pretty common modern type of strut application.


Don't forget that BMW does a lot with struts as well. There's nothing "wrong" with the concept of a strut suspension. It just has to be executed well. As Gordon Murray said "The automotive problem is fundamentally one of packaging".

The tall knuckle you describe is actually pretty terrible for camber gain. Think about the lateral distance the upper ball joint would have to cover to create a given camber change vs. the lateral distance that the UBJ would have to cover on a conventional knuckle inside the wheel.

What the tall knuckle geometry does is let designers *PACKAGE* a SLA setup in almost the same volume as a strut and get better kingpin axis packaging. That's the same reason that some MFG's use "virtual kingpin" type geometries... BMW's done that in the 5, 6 & 7 series for years, 2G DSM lower control arms are like that, as are some Audi designs. This isn't done for any geometric advantage... it's done for packaging.

Also, the tall knuckle adds significant unsprung weight.

[This message has been edited by Will (edited 07-03-2011).]

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07-03-2011 09:27 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by ccfiero350:
The lower rear frame horn in that area would not take too kindly to that kind of side load.



Why not?
(Hint: Where is most of the lateral load of the current rear suspension applied?)

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07-03-2011 09:38 AM Click Here to See the Profile for ccfiero350Click Here to Email ccfiero350Send a Private Message to ccfiero350Edit/Delete MessageReply w/QuoteDirect Link to This Post

Sorry to confuse, the sub frame handles all the point loads, spread them out and re-distribute them, the frame horn is what the sub frame bolts to. The frame horns are more about holding up that end of the car and crumble zones. If you can dent it with a small ball pein, it's probably not suited to hold a point load.

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Marvin McInnis
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07-03-2011 12:35 PM Click Here to See the Profile for Marvin McInnisClick Here to visit Marvin McInnis's HomePageSend a Private Message to Marvin McInnisEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by sspeedstreet:

This is why this forum wears me down sometimes. An idea is proposed for discussion and immediately people jump in with minutiae.



You want a simple solution to a complex problem. Such simple solutions sometimes exist in the real world, but not always. You have to understand a problem thoroughly to be able to decide if a given solution is "good enough." In the case of the Fiero, if the problem were trivial somebody would almost certainly already have done it.

[This message has been edited by Marvin McInnis (edited 07-03-2011).]

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wftb
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07-03-2011 03:14 PM Click Here to See the Profile for wftbClick Here to Email wftbSend a Private Message to wftbEdit/Delete MessageReply w/QuoteDirect Link to This Post

the rear sway bar option is something i have not bothered with .my car does not have one and handles really well with the mods and tires that i have put on .i have herb's book and it has been a big help .reading about his sway bar set up today gave me the impression it would not work properly without the bushing mods that were mentioned in most of the articles .the main reason i would like to have an upper A arm in the rear suspension would be to be able to get rid of the rear tie rods .these cause the up and down toe changes that give bump steer .i am slowly building a locost 7 and i have the front end completed and the locost usa forum has lots of builds that have adapted strut hubs to A arms .i keep thinking about buying the held bump steer kit but it does not eliminate the tie rod completely and i think i can do better .

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07-03-2011 05:15 PM Click Here to See the Profile for ccfiero350Click Here to Email ccfiero350Send a Private Message to ccfiero350Edit/Delete MessageReply w/QuoteDirect Link to This Post

I'm thinking Herb Adams train of thought on the big rear sway bar was to limit the camber/toe change by increasing rear roll stiffness. When I did this to my 88 car it had very nice turn in manners. I did not get a chance to try it out on a long sweeper though, wish I did.

Did Herb Adams do any work on 88s ?

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07-03-2011 05:45 PM Click Here to See the Profile for ccfiero350Click Here to Email ccfiero350Send a Private Message to ccfiero350Edit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by Will:

What the tall knuckle geometry does is let designers *PACKAGE* a SLA setup in almost the same volume as a strut and get better kingpin axis packaging. That's the same reason that some MFG's use "virtual kingpin" type geometries... BMW's done that in the 5, 6 & 7 series for years, 2G DSM lower control arms are like that, as are some Audi designs. This isn't done for any geometric advantage... it's done for packaging.



Kingpin angle determines how much lift and it's effect on camber when you turn. On the front end, its very important, on the rear, not so unless your designing forklifts. You don't need a lot of camber gain for the rear, just enough to counteract the roll, and you want a little toe to direct your thrust angle where you best like it.

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Tha Driver
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07-04-2011 08:19 AM Click Here to See the Profile for Tha DriverClick Here to visit Tha Driver's HomePageSend a Private Message to Tha DriverEdit/Delete MessageReply w/QuoteDirect Link to This Post

I was thinking about making upper control arms for the rear of my solo car (if I ever get the time & money to finish it). It's an '88: I was thinking simply weld brackets to the frame rail (plate it first of course) & bolt an upper A arm (or two heim ended arms) to it & the lower strut hole (as the pivot). You could use the upper strut hole for a coilover shock mount.
Can anyone with a good program make an animation of that & see if that a arm will be the right length? (or how far off it is - it's probably going to be short)
~ Paul
aka "Tha Driver"

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Will
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07-04-2011 08:43 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by ccfiero350:

Sorry to confuse, the sub frame handles all the point loads, spread them out and re-distribute them, the frame horn is what the sub frame bolts to. The frame horns are more about holding up that end of the car and crumble zones. If you can dent it with a small ball pein, it's probably not suited to hold a point load.



If you're going to anchor your upper control arm to the lower frame rail, I think it's pretty clear you'd want to fabricate a weld-in mount that can take the point loads from the control arm pivots.


 
quote
Originally posted by ccfiero350:

Kingpin angle determines how much lift and it's effect on camber when you turn. On the front end, its very important, on the rear, not so unless your designing forklifts. You don't need a lot of camber gain for the rear, just enough to counteract the roll, and you want a little toe to direct your thrust angle where you best like it.


Yep... and you suggested a tall knuckle for the rear. I was discussing why it's used and in what applications... It's used for packaging steering geometry and has significant drawbacks in terms of camber gain. I don't think it's a good thing to use in the rear of anything, much less a Fiero.

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07-04-2011 08:50 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by wftb:

Will , name me a car that has a bigger roll bar in the back .


Also, do you know *WHY* most cars have the larger bar in the front?

It has to do with weight distribution and the relationship of the centroid axis to the roll axis...

IE, "conventional wisdom" pretty much expects that the HEAVY end of the car will get the bigger bar.

Also, bigger bars make chassis tuning problems... not necessarily better handling.

[This message has been edited by Will (edited 07-04-2011).]

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07-04-2011 12:47 PM Click Here to See the Profile for Black LotusSend a Private Message to Black LotusEdit/Delete MessageReply w/QuoteDirect Link to This Post

Awhile back I made some measurements of the front and rear suspension pivot points on my '88 for a suspension program that I have.
The front roll center was a little bit HIGHER than the rear roll center. (WTF!) By eyeballing where the masses were in the car, it suggested to me that the roll center axis was out of whack with the mass axis of the car. In other words, this means the the rear overturning rolling moment was much higher than the front and explained the need for the rather large stock anti-roll bar in the back of the Fiero.
Not that this is entirely bad, as it might help the car pass whatever dynamic steering quality tests that the car had to go thru to pass GM steering and stability tests (maybe).
This would explain the feeling that the back end of the car would flop over a bit, even with Koni shocks, which was a real party killer to me because I wanted to put a big 'ol Chevy V8 in it. A big V8 would have made the car scary at the limit, or when recovering from a slide.
The only solution I could see was to put a LOT lighter engine in the back--or lower the existing package-- and raise the rear roll center.
(I would have used this opportunity to remove more weight from the front to keep the weight distribution the same, as that is just fine.)
However, raising the rear roll center puts more lateral load onto the outside rear tire in a corner and makes the car fundamentally more prone to oversteer.
Reducing or eliminating the the rear bar to compensate for the raised rear roll center aggravates the lack of rear suspension travel and would make the rear end more prone to hitting the bumpstops.
What a mess!
At this point, the EASIEST thing to do, because I am lazy, was to put all-season tires on it and and buy a different car for serious driving.




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