Click here to visit The FieroStore | View all sponsors
  Pennock's Fiero Forum
  Technical Discussion & Questions
  Redesign a Fiero suspension for better geometry (Solidworks, ProEngineer, etc) (Page 2)

Post New Topic  Post A Reply
Email This Page to Someone! | Printable Version

This topic is 10 pages long:  1   2   3   4   5   6   7   8   9   10 
Previous Page | Next Page
next newest topic | next oldest topic
Redesign a Fiero suspension for better geometry (Solidworks, ProEngineer, etc) by Austrian Import
Started on: 06-30-2011 06:13 PM
Replies: 395 (40725 views)
Last post by: 84fiero123 on 02-28-2016 10:30 AM
Will
Member

Posts: 12973
From: Where you least expect me
Registered: Jun 2000


Feedback score: (1)
Leave feedback





Total ratings: 234
Rate this member

Report this Post07-04-2011 09:01 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 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.

IP: Logged

Austrian Import
Member

Posts: 3919
From: Monterey, CA
Registered: Feb 2007


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-07-2011 03:12 AM 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 sspeedstreet:

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:


(Credit to dave@team321.com)

IP: Logged

Bloozberry
Member

Posts: 7760
From:
Registered: Jan 2009


Feedback score: N/A
Leave feedback





Total ratings: 307
Rate this member

Report this Post07-07-2011 07:17 AM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post

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?

IP: Logged

sspeedstreet
Member

Posts: 2249
From: Santa Maria, CA
Registered: Dec 2002


Feedback score:    (18)
Leave feedback





Total ratings: 53
Rate this member

Report this Post07-07-2011 12:18 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:

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?


Yes.

IP: Logged

Austrian Import
Member

Posts: 3919
From: Monterey, CA
Registered: Feb 2007


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-07-2011 12:49 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

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.

IP: Logged

Austrian Import
Member

Posts: 3919
From: Monterey, CA
Registered: Feb 2007


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-07-2011 01:07 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

These articles are pretty similar to articles that got me thinking about suspension designs in the first place:

http://www.modified.com/tec...ck_part_1/index.html
http://www.modified.com/tec...ck_part_2/index.html
http://www.modified.com/tec...ck_part_3/index.html
http://www.modified.com/tec...ck_part_4/index.html
http://www.modified.com/tec...ck_part_5/index.html
http://www.modified.com/tec...ck_part_6/index.html

http://www.rc-truckncar-tun...com/roll-center.html

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).]

IP: Logged

Austrian Import
Member

Posts: 3919
From: Monterey, CA
Registered: Feb 2007


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-07-2011 01:30 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

Another good suspension primer: http://www.mae.ncsu.edu/kla...nDesignCaseStudy.ppt

BMW suspension: http://www.e30m3project.com...oll_center/index.htm

Roll center article: http://www.neohio-scca.org/...e%20Dynamics2007.pdf

Good books on the topic:
http://books.google.com/boo...#v=onepage&q&f=false
http://www.amazon.com/How-M...d=1310059392&sr=1-11 <-- ancient book, but still one of the best.
http://www.amazon.com/Compe...d=1310059448&sr=1-28
http://www.amazon.com/Autom...d=1310059468&sr=1-44
http://www.amazon.com/Vehic...d=1310059488&sr=1-54
http://www.amazon.com/Suspe...d=1310059513&sr=1-72

IP: Logged

Bloozberry
Member

Posts: 7760
From:
Registered: Jan 2009


Feedback score: N/A
Leave feedback





Total ratings: 307
Rate this member

Report this Post07-07-2011 06:30 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 Austrian Import:

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

IP: Logged

sspeedstreet
Member

Posts: 2249
From: Santa Maria, CA
Registered: Dec 2002


Feedback score:    (18)
Leave feedback





Total ratings: 53
Rate this member

Report this Post07-07-2011 08:53 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

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.

Thanks again, I've been schooled.

~Neil

IP: Logged

Bloozberry
Member

Posts: 7760
From:
Registered: Jan 2009


Feedback score: N/A
Leave feedback





Total ratings: 307
Rate this member

Report this Post07-07-2011 10:36 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:

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?


Exactly.

IP: Logged

Knight
Member

Posts: 364
From: Tampa, FL
Registered: Apr 2006


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-07-2011 11:55 PM Click Here to See the Profile for KnightSend a Private Message to KnightEdit/Delete MessageReply w/QuoteDirect Link to This Post

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).]

IP: Logged

Knight
Member

Posts: 364
From: Tampa, FL
Registered: Apr 2006


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-08-2011 12:19 AM Click Here to See the Profile for KnightSend a Private Message to KnightEdit/Delete MessageReply w/QuoteDirect Link to This Post

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.

Any thoughts?

IP: Logged

kennn
Member

Posts: 263
From: Green Valley, AZ USA
Registered: Apr 2006


Feedback score: (2)
Leave feedback

Rate this member

Report this Post07-08-2011 11:11 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

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).]

IP: Logged

Will
Member

Posts: 12973
From: Where you least expect me
Registered: Jun 2000


Feedback score: (1)
Leave feedback





Total ratings: 234
Rate this member

Report this Post07-09-2011 07:42 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:

Yes, the tire moves into negative camber, but the "still" pictures only tell part of the story.



Another part of the story is the loss of camber through bushing compression.

IP: Logged

ccfiero350
Member

Posts: 822
From: Houston, Texas
Registered: Feb 2003


Feedback score: (2)
Leave feedback

Rate this member

Report this Post07-09-2011 01:03 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 Bloozberry:


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

IP: Logged

Knight
Member

Posts: 364
From: Tampa, FL
Registered: Apr 2006


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-11-2011 01:23 AM Click Here to See the Profile for KnightSend a Private Message to KnightEdit/Delete MessageReply w/QuoteDirect Link to This Post

Bump for an awesome thread. Please people, put forth some ideas.

IP: Logged

Austrian Import
Member

Posts: 3919
From: Monterey, CA
Registered: Feb 2007


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-15-2011 03:19 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 Bloozberry:


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.

IP: Logged

sspeedstreet
Member

Posts: 2249
From: Santa Maria, CA
Registered: Dec 2002


Feedback score:    (18)
Leave feedback





Total ratings: 53
Rate this member

Report this Post07-15-2011 03:40 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 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.

IP: Logged

sspeedstreet
Member

Posts: 2249
From: Santa Maria, CA
Registered: Dec 2002


Feedback score:    (18)
Leave feedback





Total ratings: 53
Rate this member

Report this Post07-27-2011 12:30 AM 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 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).

A couple of vids:

http://www.youtube.com/watch?v=o93DBadnHWs

http://www.youtube.com/watch?v=VyAc6YPGBa0

[This message has been edited by sspeedstreet (edited 07-27-2011).]

IP: Logged

Will
Member

Posts: 12973
From: Where you least expect me
Registered: Jun 2000


Feedback score: (1)
Leave feedback





Total ratings: 234
Rate this member

Report this Post07-27-2011 07:07 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 sspeedstreet:

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.

http://i17.photobucket.com/...street/Tightleft.jpg

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).

A couple of vids:

http://www.youtube.com/watch?v=o93DBadnHWs

http://www.youtube.com/watch?v=VyAc6YPGBa0




*ANY* discussion of suspension that doesn't begin and end with tires is meaningless.

IP: Logged

sspeedstreet
Member

Posts: 2249
From: Santa Maria, CA
Registered: Dec 2002


Feedback score:    (18)
Leave feedback





Total ratings: 53
Rate this member

Report this Post07-27-2011 10:58 AM 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 Will:

*ANY* discussion of suspension that doesn't begin and end with tires is meaningless.


You stopped me with that one. Please explain.

IP: Logged

bse53
Member

Posts: 58
From: Moses Lake
Registered: Jul 2011


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-27-2011 12:08 PM Click Here to See the Profile for bse53Send a Private Message to bse53Edit/Delete MessageReply w/QuoteDirect Link to This Post

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:

http://www.youtube.com/watch?v=R4N3r1u_K_Y


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.

IP: Logged

Will
Member

Posts: 12973
From: Where you least expect me
Registered: Jun 2000


Feedback score: (1)
Leave feedback





Total ratings: 234
Rate this member

Report this Post07-27-2011 01:55 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 sspeedstreet:

You stopped me with that one. Please explain.


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).]

IP: Logged

ccfiero350
Member

Posts: 822
From: Houston, Texas
Registered: Feb 2003


Feedback score: (2)
Leave feedback

Rate this member

Report this Post07-27-2011 02:11 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 sspeedstreet:

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

IP: Logged

sspeedstreet
Member

Posts: 2249
From: Santa Maria, CA
Registered: Dec 2002


Feedback score:    (18)
Leave feedback





Total ratings: 53
Rate this member

Report this Post07-27-2011 02:42 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

All righty. 205/60/15 fronts on 6.5" rims, 215/60/15 on 7.0" rims at the rear.

IP: Logged

bse53
Member

Posts: 58
From: Moses Lake
Registered: Jul 2011


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-27-2011 03:09 PM Click Here to See the Profile for bse53Send a Private Message to bse53Edit/Delete MessageReply w/QuoteDirect Link to This Post

"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.

IP: Logged

Will
Member

Posts: 12973
From: Where you least expect me
Registered: Jun 2000


Feedback score: (1)
Leave feedback





Total ratings: 234
Rate this member

Report this Post07-27-2011 05:23 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 bse53:

"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.

IP: Logged

bse53
Member

Posts: 58
From: Moses Lake
Registered: Jul 2011


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-28-2011 11:23 AM Click Here to See the Profile for bse53Send a Private Message to bse53Edit/Delete MessageReply w/QuoteDirect Link to This Post

Speedstreet-

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.

IP: Logged

Will
Member

Posts: 12973
From: Where you least expect me
Registered: Jun 2000


Feedback score: (1)
Leave feedback





Total ratings: 234
Rate this member

Report this Post07-28-2011 12:37 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 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?

IP: Logged

bse53
Member

Posts: 58
From: Moses Lake
Registered: Jul 2011


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-28-2011 01:00 PM Click Here to See the Profile for bse53Send a Private Message to bse53Edit/Delete MessageReply w/QuoteDirect Link to This Post

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.



Brian

IP: Logged

sspeedstreet
Member

Posts: 2249
From: Santa Maria, CA
Registered: Dec 2002


Feedback score:    (18)
Leave feedback





Total ratings: 53
Rate this member

Report this Post07-28-2011 01:25 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 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.

IP: Logged

bse53
Member

Posts: 58
From: Moses Lake
Registered: Jul 2011


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-28-2011 01:46 PM Click Here to See the Profile for bse53Send a Private Message to bse53Edit/Delete MessageReply w/QuoteDirect Link to This Post

sspeedstreet,

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.

IP: Logged

Will
Member

Posts: 12973
From: Where you least expect me
Registered: Jun 2000


Feedback score: (1)
Leave feedback





Total ratings: 234
Rate this member

Report this Post07-28-2011 02:01 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 bse53:

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.

http://i152.photobucket.com...se53/06222011317.jpg

Brian


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).]

IP: Logged

sspeedstreet
Member

Posts: 2249
From: Santa Maria, CA
Registered: Dec 2002


Feedback score:    (18)
Leave feedback





Total ratings: 53
Rate this member

Report this Post07-28-2011 02:29 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

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.

IP: Logged

bse53
Member

Posts: 58
From: Moses Lake
Registered: Jul 2011


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-28-2011 02:30 PM Click Here to See the Profile for bse53Send a Private Message to bse53Edit/Delete MessageReply w/QuoteDirect Link to This Post

Funny you should ask about heat in the tires.

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.

IP: Logged

Will
Member

Posts: 12973
From: Where you least expect me
Registered: Jun 2000


Feedback score: (1)
Leave feedback





Total ratings: 234
Rate this member

Report this Post07-28-2011 05:06 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 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.


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).]

IP: Logged

Will
Member

Posts: 12973
From: Where you least expect me
Registered: Jun 2000


Feedback score: (1)
Leave feedback





Total ratings: 234
Rate this member

Report this Post07-28-2011 05:16 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 bse53:

Funny you should ask about heat in the tires.

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.

IP: Logged

KurtAKX
Member

Posts: 4006
From: West Bloomfield, MI
Registered: Feb 2002


Feedback score:    (9)
Leave feedback





Total ratings: 128
Rate this member

Report this Post07-29-2011 08:56 AM Click Here to See the Profile for KurtAKXSend a Private Message to KurtAKXEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by bse53:

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.

IP: Logged

bse53
Member

Posts: 58
From: Moses Lake
Registered: Jul 2011


Feedback score: N/A
Leave feedback

Rate this member

Report this Post07-29-2011 09:35 AM Click Here to See the Profile for bse53Send a Private Message to bse53Edit/Delete MessageReply w/QuoteDirect Link to This Post

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.

http://www.rhoadescamaro.com/build/?page_id=481

For that matter, looking at his next car.

IP: Logged

Will
Member

Posts: 12973
From: Where you least expect me
Registered: Jun 2000


Feedback score: (1)
Leave feedback





Total ratings: 234
Rate this member

Report this Post07-30-2011 09:23 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 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.


 
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.

IP: Logged

Previous Page | Next Page

This topic is 10 pages long:  1   2   3   4   5   6   7   8   9   10 
next newest topic | next oldest topic

All times are ET (US)

Post New Topic  Post A Reply
Hop to:

Contact Us | Back To Main Page

Advertizing on PFF | Fiero Parts Vendors
PFF Merchandise | Fiero Gallery | Ogre's Cave
Real-Time Chat | Fiero Related Auctions on eBay



Copyright (c) 1999, C. Pennock