Originally posted by Black Lotus: 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.
Not really... -The equation for weight transfer includes Cg height, track width and lateral G. -Raising the rear roll center reduces the rear roll moment by shortening the moment arm between the centroid axis and the roll axis. -A rear-heavy car with minimal tire stagger will *ALWAYS* be prone to oversteer, no matter how good the suspension is. The way to fix this is with tire sizes, not suspension geometry or tuning.
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.
Thank you! At least one person understands the idea behind this thread. Hopefully we can get back on track and discuss the major parts of suspension design prior to minutia of ball-joints, heim joints, etc.
Stuff like this below is the beginning of what I had in mind for this thread:
quote
Originally posted by sspeedstreet: I've been thinking of the same things. I was looking at the Mustang SLA setup as well. The Fiero design [...snip...] 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:
Interesting, because if that's what you wanted, then your opening post shouldn't have lead us astray by stating you wanted:
quote
Originally posted by Austrian Import:
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.
and:
quote
Originally posted by Austrian Import:
The goal is to APPLY what engineers have learned about suspension design in the last 30 years since the Fiero was built.
and:
quote
Originally posted by Austrian Import:
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),
4) provide an avenue to share TECHNICAL INFORMATION/CONTENT for people with similar interests.
Almost all of the posts in this thread to date have been in accordance with what you stated you wanted in your opening post. Am I (and nearly everyone else) missing something here?
Interesting, because if that's what you wanted, then your opening post shouldn't have lead us astray by stating you wanted:
Almost all of the posts in this thread to date have been in accordance with what you stated you wanted in your opening post. Am I (and nearly everyone else) missing something here?
I guess what I was hoping for was models of suspension designs and then discussing the benefits/drawbacks of each. I also was hoping to start in more general terms and then get into the details as the thread progresses. It seemed to me that talking about balljoints, is like "dotting the i's" before we have figured out geometry designs in rough form.
And yes, I'm not dismissing a strut type setup, IF it's a better setup than other choices.
What I'm hoping for eventually is simulations of various suspension designs (with regards to feasability on a Fiero) from which we can discuss the benefits/drawbacks of each.
I copied the pictures out of the articles for easy reference. I think they explain the basics well and should help get everybody on the same page. I hope we will be able to find Fiero specific suspension pictures to use as a baseline for discussions. (Hope the Factory manual has these)
[This message has been edited by Austrian Import (edited 07-07-2011).]
I hope we will be able to find Fiero specific suspension pictures to use as a baseline for discussions. (Hope the Factory manual has these)
OK, now you're talking. I'll be glad to contribute if this is going to be a structured analysis of suspension system performance. IMHO, this is the way any suspension improvement should be undertaken; by defining the limitations of the status quo, then determining if there are improvements that can be made, and how they can be implemented. Whether that involves minor tweaks or whole scale redesign isn't something that should be determined until you know what the current system does. How else could anyone possibly know that another system is better? I lack the ability to judge the performance of a system by its looks, though some seem to be able to do so.
So, to get the ball rolling in the direction you want, I'll repost the drawings of the '88 rear suspension geometry from my build thread. They're not 100% accurate, but I spent roughly 150 hours measuring and drafting the rear suspension system on an '88 to come up with them. The accuracy is within GM's own stated frame alignment tolerances of plus or minus 3 mm. I doubt you'll find official factory drawings or data. None of the service manuals have this information, neither did an exhaustive search of the internet turn up anything, and GM Customer Services said they no longer have the information either (yeah right).
'88 Stock Rear Suspension Rear View
'88 Stock Rear Suspension Side View
'88 Stock Rear Suspension Top View
Determination of Stock '88 Rear Suspension Roll Center
Determination of Stock '88 Rear Suspension Dynamic Roll Centers
Determination of Stock '88 Rear Suspension % Anti Squat
Determination of Stock '88 Rear Suspension Camber Change
Determination of Stock '88 Rear Suspension Toe Change
Bloozberry, those drawings are superb! That's more Fiero rear suspension data in one spot than the total I'd ever seen before. Thanks for posting those for us. Honest, I will shut up and listen to what you have to offer.
A question: In your "Determination of Stock '88 Rear Suspension Camber Change" diagram, you are showing lateral link parallel with the ground and 0 degree camber at the static ride height. At 76mm jounce the tire actually moves into negative camber? Is this due to the angle of the strut axis during compression? I guess that's why the '88 was redesigned with the upper strut mount moved inward? Well, I had that all wrong in my head.
Also interesting is how the roll center drops like a stone as the suspension is compressed. That's why my car seemed to have a rapidly increasing body roll as I pushed harder in the corners. Self-actuating roll. Now I see the real benefit of SLA setups; less to do with camber (as I had thought) and more to do with body roll.
A question: At 76mm jounce the tire actually moves into negative camber? Is this due to the angle of the strut axis during compression?
Yes, the tire moves into negative camber, but the "still" pictures only tell part of the story. First, you have to consider that the static camber on a Fiero rear alignment is set at -1.0*, not zero as I have depicted it. So to get real world values, you have to subtract 1.0* from the camber angles shown in both rebound and jounce too. Then, consider that the Macpherson strut is designed to gain negative camber as long as the lower control arm and strut axis form an angle of less than 90 degrees. Although it's hard to measure this angle in the posted version of the drawings, I can do it on the originals much easier. What it shows is that from 76mm rebound (full extension) the angle between the lower control arm and the strut axis is about 64*, so as it travels upwards from there in jounce, it gains negative camber, ie the camber angle of the wheel moves from +2.2* towards zero. By the time the suspension is at 76mm jounce (full compression), the angle between the lower control arm and the strut axis is up to 85*, but not yet past 90*. This means that the camber curve remains on the correct side of 90* between these two limits of jounce and rebound, but the rate of camber change reduces quickly as you near full jounce. If improvements could be made, I would increase the rate at which the camber changes between the two limits.
quote
Originally posted by sspeedstreet:
I guess that's why the '88 was redesigned with the upper strut mount moved inward?
I am so excited reading this thread. I have been wondering how we can make our cars handle as well as any non exotic sports car without removing so much that its not really a Fiero anymore. I can't wait to see where this thread goes. I just love this car so much that I want to impress others with how great a car the Fiero is.
I love this site and all the truely knowledgeable people on it.
Anybody got any info on the 84-87 like Bloozberry has on the 88? Or is the 84-87 rear beyond hope?
[This message has been edited by Knight (edited 07-07-2011).]
Would a multi-link upper instead of an upper control arm work, to get around the space limitations on the passenger side? Might have to relocate the battery. Sorry, my car is out of town for the next 7 weeks so I can't eyeball anything.
Would tilting the cradle on the 84-87 help with squat? I know that I would have to modify the engine mounts to level the engine/trans. I already plan on relocating the outer tie rod attachment points to minimize bump steer. If Bump steer and pro-squat rear characteristics could be fixed, would the 88 be much of a noticeable improvement to be worth the effort for a cradle swap? Let's assume poly suspension bushings and solid metal cradle mounts. Still have to deal with 84-87 front suspension as I hear a 88 front swap is too much of a PITA.
For me the question that is begged is, could the front roll center be lowered? For the upper A-arm on the '88, the inside pivot looks to be higher at rest than the ball joint/knuckle joint. If the inside pivot could be lowered, wouldn't that also lower the front roll center and provide a more beneficial camber change curve?
Edit: Two things: First, it appears in essence that's what ccfiero350 has done with the Saturn knuckle and new upper A-arm; Second, I neglected to see that there was a whole second page. Sorry.
Ken
------------------ '88 Formula V6 '88 GT TPI V8
[This message has been edited by kennn (edited 07-08-2011).]
This is the way any suspension improvement should be undertaken; by defining the limitations of the status quo, then determining if there are improvements that can be made, and how they can be implemented. Whether that involves minor tweaks or whole scale redesign isn't something that should be determined until you know what the current system does. How else could anyone possibly know that another system is better?
Yep, Bloozberry hit it on the head. I would start out a kinematic study with some animations of the stock 88 setup, then one thats lowered, then another with some simple mods that most people can do, then one with mods that only a handful of people crazy enough will try.
------------------ yellow 88 GT, not stock white 88 notchie, 4 banger
OK, now you're talking. I'll be glad to contribute if this is going to be a structured analysis of suspension system performance. IMHO, this is the way any suspension improvement should be undertaken; by defining the limitations of the status quo, then determining if there are improvements that can be made, and how they can be implemented. [..] SNIP [...]
Yea, that's what I meant originally. Maybe I should have specified better at the beginning. I guess that's why threads are "living documents" that grow with each contribution. Glad to see I'm not the only one interested in this.
I have another auto-cross on the 23rd an will get some close-up video of the car in the corners. I just finished installing my poly-Delrin custom toe and lateral rear links and had it aligned (1.5* negative camber, 1/8" toe-in), so I don't expect the suspension deflection to be a big factor this time. We'll see what the rear looks like under load.
This is the best shot I got of the suspension compressed in a corner. Stock swaybars with poly mounts and heim joint ends, 280 lb/in front springs and 350 lb/in rears, Koni shocks, all poly on the rear links, stock bushings on the front and and stock tire sizes all around (Yoko AVIDs). The car is lowered 1.5 inches in the front and 1.0 inch in the rear.
The car was neutral with under or over steer easily induced (over steer VERY easy to induce). The tires seemed to be wearing evenly all around as there didn't seem to be a lot of positive camber in the corners. There is a lot of body roll however and this leads to a tail happy condition when power is applied. So there it is, The camber curve isn't the problem, it's the falling roll center (which I am just now getting my head around).
This is the best shot I got of the suspension compressed in a corner. Stock swaybars with poly mounts and heim joint ends, 280 lb/in front springs and 350 lb/in rears, Koni shocks, all poly on the rear links, stock bushings on the front and and stock tire sizes all around (Yoko AVIDs). The car is lowered 1.5 inches in the front and 1.0 inch in the rear.
The car was neutral with under or over steer easily induced (over steer VERY easy to induce). The tires seemed to be wearing evenly all around as there didn't seem to be a lot of positive camber in the corners. There is a lot of body roll however and this leads to a tail happy condition when power is applied. So there it is, The camber curve isn't the problem, it's the falling roll center (which I am just now getting my head around).
If you're going to view camber changes throughout suspension travel, try putting the camera under the car, like this video, using an inexpensive 'spy' camera:
This is a great thread for me, as I just purchased a dedicated autocross Fiero. I just ordered a couple of cameras like the one used in the video. It might help me understand what's happening as I try different ride heights.
I'm guessing the focus of the thread though, is in street driven, performance oriented designs.
You didn't mention what size tires you have. There's basically nothing you can do about oversteer on a rear-heavy car with a square tire fitment, for example.
Tires make a car handle. Period. The only reason to concern ourselves with suspension design is to make the best use of the tires.
[This message has been edited by Will (edited 07-27-2011).]
This is the best shot I got of the suspension compressed in a corner. Stock swaybars with poly mounts and heim joint ends, 280 lb/in front springs and 350 lb/in rears, Koni shocks, all poly on the rear links, stock bushings on the front and and stock tire sizes all around (Yoko AVIDs). The car is lowered 1.5 inches in the front and 1.0 inch in the rear.
Looks like he did mention his tires, maybe because it was not the first or last thing he wrote about, it was in the middle.
------------------ yellow 88 GT, not stock white 88 notchie, 4 banger
"There's basically nothing you can do about oversteer on a rear-heavy car with a square tire fitment, for example."
Is this always true? Can't I just stiffen up the front until it understeers, stiffen up the back until it oversteers, then back off a bit on the rear?
Aren't staggered tire sizes just one of the many compromises?
Isn't this thread about designing a suspension that doesn't necessarily require that design compromise?
I'm asking the question, because I'm going to try a square setup on my autocross car, going from 10" front- 12" rear wheels to 10" all around.
For a car with other than 50/50 weight distribution, staggered is the ideal. Tire width should match the weight distribution. Square is the compromise (usually in the name of lower cost).
If you tune the suspension against the natural tendency you get from the contact pressure balance front/rear, then you get what the Fiero was stock... understeer up to the limit, then rapid transition to oversteer.
Looking at your picture, it appears the rear tire has moved into positive camber, as has the front.
This discussion seems to be focusing on the rear suspension, but the front suspension has it's own issues.
I realize the thrust of this thread relates to engineering a suspension, but I would look at the S2000 suspension. The S2000 owns BS in autocross, replacing the C4 Corvette as the car to own.
In your design I wouldn't ignore the weight distribution issue either. I'd be moving the rear wheel as far back as I could given the limitation of the engine transmission package.
Originally posted by bse53: I'm asking the question, because I'm going to try a square setup on my autocross car, going from 10" front- 12" rear wheels to 10" all around.
What problem are you trying to solve with this change?
Narrow is good in autocross, all things being equal. As you can see, the 12" wheels (with 5.5" backspace) stick out a ways. 10" wheels narrow the car by 4".
12" wheels require racing slicks (there are no autocross size 15" tires to fit) and consequently I'm not sure I can build heat quick enough to make use of the potential extra grip of the wider tires.
I have no interest in dedicating my car to track use only . Wide sticky tires, stiffer springs and higher rate sway bars only mask an inherently poor suspension design. Reducing body roll by design would be my goal. Then the spring rate in the rear could be reduced to make the car stick better in wet or uneven road surfaces i.e., The Real World.
I'm not trying to highjack this thread, which I find fascinating, and autocrossing a stock car is just as much fun as a modified one-- but for different reasons.
I was autocrossing a c4 Corvette in AS (now BS). As you are aware stock classes severely limit your ability to modify the car-- the only alterations are shocks, front sway bar and tires. To be competitive in stock classes, you'll need the biggest sticky tires you can stuff on stock rims and stiff shocks on rebound. Don't think a bigger front bar would help. I think you probably want more static negative camber- both front and rear.
I'll keep quiet now, and hopefully the discussion will resume about how to improve the Fiero's suspension.
Narrow is good in autocross, all things being equal. As you can see, the 12" wheels (with 5.5" backspace) stick out a ways. 10" wheels narrow the car by 4".
12" wheels require racing slicks (there are no autocross size 15" tires to fit) and consequently I'm not sure I can build heat quick enough to make use of the potential extra grip of the wider tires.
Are you having oversteer problems because your rear tires are too cold?
quote
Originally posted by sspeedstreet:
I have no interest in dedicating my car to track use only . Wide sticky tires, stiffer springs and higher rate sway bars only mask an inherently poor suspension design. Reducing body roll by design would be my goal. Then the spring rate in the rear could be reduced to make the car stick better in wet or uneven road surfaces i.e., The Real World.
"Wide sticky tires... mask an inherently poor suspension design" Say what?
Flat cornering is not the same as good handling... A Lotus Elise/Exige is one of the best handling cars on the market, yet has a lot of body roll by modern standards.
Also remember that gokarts corner flat and have NO suspension.
[This message has been edited by Will (edited 07-28-2011).]
By mask I mean be capable of more lateral g than, say, a street tire. Take any suspension design, good or bad. Will it produce better lap times on typical street tires or race tires? Does that mean the suspension becomes better at controlling the contact patch because it has wider, sticky tires? No, it only means the shortcomings of a given design become apparent at a higher limit.
When I got the car, it had some old hard racing slicks. I bought some tak-offs from a guy in Michigan that were supposedly fresh.
The car understeered like a pig-- that is until it spun out. Totally unpredictable. I worked the understeer out (somewhat), but I was still way behind where I should be time wise, based on the history of the car. My assumption was that I wasn't getting heat in the tires, since it's been a cold spring and the car came from Arizona where heat in the tires isn't an issue.
Talked to the supplier in Michigan and he sent me out another set-- but this time 4 9.5" slicks. I crammed them on some 8" stock rims and even as pinched as they were, the difference was night and day.
The first set he sent me were already cycled out, even though they still had plenty of tread.
Since I only have two 10" rims, I'm going to put two of the newer tires on those and put the 8" wheels up front (effectively leaving me with some stagger).
But I still think the narrower wheels may be faster.
As to body roll-- the most impressive car I see autocrossing are the BMW's in stock classes. They have lots of body roll and are incredibly quick cars. It's rather amazing actually.
Another reason why I'd look at the S2000 geometry though, is the "in-wheel" design.
By mask I mean be capable of more lateral g than, say, a street tire. Take any suspension design, good or bad. Will it produce better lap times on typical street tires or race tires? Does that mean the suspension becomes better at controlling the contact patch because it has wider, sticky tires? No, it only means the shortcomings of a given design become apparent at a higher limit.
A car with great tires and crappy suspension will out drive a car with great suspension and crappy tires.
Tires > suspension
Also, if you put a specific type/size/stagger of tire on a car, dial in the suspension, then change to significantly different type/size/stagger, you'll have to retune the suspension.
It's all part of the package. Getting max performance involves matching everything. The matching process has to begin and end with tires.
[This message has been edited by Will (edited 07-28-2011).]
When I got the car, it had some old hard racing slicks. I bought some tak-offs from a guy in Michigan that were supposedly fresh.
The car understeered like a pig-- that is until it spun out. Totally unpredictable. I worked the understeer out (somewhat), but I was still way behind where I should be time wise, based on the history of the car. My assumption was that I wasn't getting heat in the tires, since it's been a cold spring and the car came from Arizona where heat in the tires isn't an issue.
Talked to the supplier in Michigan and he sent me out another set-- but this time 4 9.5" slicks. I crammed them on some 8" stock rims and even as pinched as they were, the difference was night and day.
The first set he sent me were already cycled out, even though they still had plenty of tread.
Since I only have two 10" rims, I'm going to put two of the newer tires on those and put the 8" wheels up front (effectively leaving me with some stagger).
But I still think the narrower wheels may be faster.
As to body roll-- the most impressive car I see autocrossing are the BMW's in stock classes. They have lots of body roll and are incredibly quick cars. It's rather amazing actually.
Another reason why I'd look at the S2000 geometry though, is the "in-wheel" design.
There certainly can be such a thing as too much tire, depending on the weight of the car, tire compound, time available to build heat, etc.
I agree that an "in-wheel" knuckle on a SLA suspension is better than a "tall knuckle" with the UBJ above the top of the tire.
What you said about BMW's basically defines good geometry... allows the car to make the best use of its tires. Traction makes a car quick. The quickest car is the car that's able to exercise the most traction throughout the course. Exercising traction involves making the best use of your tires.
Narrow is good in autocross, all things being equal. As you can see, the 12" wheels (with 5.5" backspace) stick out a ways. 10" wheels narrow the car by 4".
Narrow is good. It's interesting to watch just how much less a narrow car has to work through an autocross slalom than a wide car.
One of the better autocross drivers did an analysis of what are the important elements needed in an autocross run. Here's the breakdown of a 59.18 second run at a national event: Transitions: 24.27 seconds, 41.01%
Skidpad: 23.25 seconds, 39.29%
Entry: 5.16 seconds, 8.72%
Pure Accel: 3.67 seconds, 6.2%
Pure Braking: .59 seconds, 1%
And if you further boil those down you get these:
Primarily turning: 80.3%
Primarily slowing down: 9.72%
Primarily speeding up: 9.99%
Narrow helps in transitions. Low cg and track width helps with skidpad.
Byron Short did the math in transitions. Car A is 66" wide. Car B is 72.5" wide. Assuming the same lateral g's, car A will have a .2 second advantage after 5 cones. Any autocrosser would benefit from reading his analysis.
I have no interest in dedicating my car to track use only . Wide sticky tires, stiffer springs and higher rate sway bars only mask an inherently poor suspension design. Reducing body roll by design would be my goal. Then the spring rate in the rear could be reduced to make the car stick better in wet or uneven road surfaces i.e., The Real World.
quote
Originally posted by sspeedstreet:
By mask I mean be capable of more lateral g than, say, a street tire. Take any suspension design, good or bad. Will it produce better lap times on typical street tires or race tires? Does that mean the suspension becomes better at controlling the contact patch because it has wider, sticky tires? No, it only means the shortcomings of a given design become apparent at a higher limit.
I agree that a good suspension design makes the best use of the tires. It does this by keeping the relationship of the tire to the pavement such that contact pressure is even across the face of the tire despite body roll and lateral squirm of the tire when loaded.
I do not agree that the geometry should be used to limit body roll. This deprives the driver of the ability to feel the chassis load up.
The shortcomings of a given design will become apparent with appropriate testing and observation... such as using a pyrometer to measure surface temps across the width of the tread or observing tire wear patterns.
