Is the Ackerman angle on the 88 really bad? It looks it. (Page 3/5)
Patrick JUN 28, 03:13 PM

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Originally posted by 82-T/A [At Work] Here:

Hahah...



Todd, why do you almost always copy/quote the entire post that you're responding to? Text is bad enough, but you also include images when they're present. Not trying to give you a bad time, but all it does is necessitate a whole lot of extra scrolling for everyone over duplicated material when reading the thread.
82-T/A [At Work] JUN 28, 11:22 PM

quote
Originally posted by Patrick:

Todd, why do you almost always copy/quote the entire post that you're responding to? Text is bad enough, but you also include images when they're present. Not trying to give you a bad time, but all it does is necessitate a whole lot of extra scrolling for everyone over duplicated material when reading the thread.



I only quote an image if I'm referencing that specifically in my response (at least within the past couple of years).

But it's OK to quote the message itself (just the text)... sometimes I abbreviate it, but the unwritten rule is only about quoting images unnecessarily.
Patrick JUN 28, 11:41 PM

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Originally posted by 82-T/A [At Work]:

I only quote an image if I'm referencing that specifically in my response (at least within the past couple of years).



I won't do it here... but I'll demonstrate to you that this is simply untrue. I don't think you realize how often you just quote everything for no practical purpose.


quote
Originally posted by 82-T/A [At Work]:

...but the unwritten rule is only about quoting images unnecessarily.



I don't know what "rule" you're referring to, but it's just common sense not to quote a whole lot of text for no reason... especially when you're responding immediately below the post you've quoted in full.

CLICK FOR FULL SIZE

[This message has been edited by Patrick (edited 06-29-2024).]

Yellow-88 JUN 29, 12:25 AM

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Originally posted by ceverhart:

please continue Yellow -88



Hi

Thanks for asking. This is my favorite car subject and I enjoy sharing it.

We often hear the term handling used interchangeably with the term cornering. They are related but separate. Cornering forces can be measured in the lab. Handling is something a driver “feels”. This will first be about “cornering”.

A chassis is 4 tire contact patches bearing the cars mass; Ideally, equally distributed over the 4 contact patches. The Fiero is already close to that. And, almost all of the mass is inside the wheelbase. That leads to low polar moment of inertia ... and makes the physics much easier.

Step one in tuning a chassis; the 88 only requires tuning and not a redesign like the early cars; is to make it able to roll perfectly straight with the least possible resistance. All 4 tire radial planes need to be parallel to each other and to the roll axis. Ideally they will stay that way regardless of bump or droop movements. If there is zero toe angle change over about 4” off travel between bump and droop, it can be called zero bump steer. (for all practical purposes) The 88 front end is there already.

If tires are steering in slightly different directions at every undulation, their just scrubbing rubber from their contact patches fighting each other. That’s lost energy that needs to be made up with more power. If feels uncomfortable too.

Later, Yellow-88
Yellow-88 JUN 29, 10:21 AM

I could not find any discussion about the factory ackerman angles on the 88.[/QUOTE]

You won't find any because "Akerman" is not and angle. Ackerman is the principal that the inside steering tire will follow a shorter radius than the outside steering tire. Projected axel centerlines will meet at the same point.

82-T/A [At Work] JUN 29, 11:37 AM

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Originally posted by Patrick:

I don't know what "rule" you're referring to...





Exactly...
longjonsilver JUN 29, 12:48 PM

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Originally posted by Raydar:
But one of the old school Fiero autocrossers - his name escapes me - found that the most responsive (best turn-in) combination was an earlier front suspension (he had an 85) with an 88 rear cradle swapped in.
He also ran a 4.9/Isuzu combination. Some of you may remember him. Haven't seen him post for years.
He also ran the Cadero Usenet group. (Dating myself, here.)



i remember him. He was from Oklahoma City if i remember correctly. He had raced his Fiero extensively with a Quad Four and then built a car with the 4.9 engine that he said was superior. i also remember his advocacy of the earlier front end with the 88 rear cradle swapped in. He almost convinced me to do likewise.


quote
Originally posted by Yellow-88:
I'll continue this if anybody's interested.



And Yellow - keep it up. i am listening

------------------
Astronomy says we will find a coded signal from outer space. Then we'll KNOW that life exists there, for coded signals aren't by chance.

Biology says there are coded genetic signals in every cell, but we KNOW that no intelligence created life.

I'm the original owner of a white ' 84 2M4 purchased Dec 10, 1983 from Pontiac. Always garaged, no rust, 3800SC, 4-wheel drifts are fun!

Yellow-88 JUN 29, 10:57 PM
Hi.

So now that we have a chassis that can roll perfectly straight and can absorb surface irregularities without scuffing any of its contact patches. We can introduce some forces to it. Call them simply; the forces that cause roll angle change.

By projecting the roll axis, it forms a plane perpendicular to the road surface plane, virtually dividing the chassis into left and right side. Any variation from perpendicular is roll angle.

Introducing roll angle transfers weight to the side with the smallest angle. Because gravity is involved, the contact patches on that side now carry a higher percentage of the chassis weight. Roll should transfer weight to front and rear contact patches equally. A properly sized roll bar does that.
Things get tricky real fast when one divides the chassis into sprung and un-sprung weight. Now it becomes suspension … suspended with springs and levers. Gravity gets involved.

At this point the fancy physics and math leads to a simple result. Roll causes weight transfer and that compress a spring that balances the load. The equal and opposite forces thing. It also moves the control arm toward bump in the process. It doesn’t cause bump steer because we” set” that in step one. But what happens to the camber angles?

A well designed Double A arm Suspension system will compensate for camber change caused by roll angle. Zero camber at maximum roll angle is ideal. That’s when springs can no longer balance the transferred load, so the over loaded contact patches reach their limit of adhesion. Adding extra negative camber to compensate may help with high aspect ratio, 60 plus series tires, because they may distort enough to actually keep a full contact foot print. Low profile tires want to be at zero camber for maximum contact … always. Naturally my pitch for the 88. Somebody already thought all that stuff out.

We haven't entered any steering inputs yet so Please stand by.

A thought; If any of you 3D Cad guys with scanners what to model the 88 front end, that would be wicked cool. I'm a pioneer dinosaur in the Cad Modeling field.
Carter, wanna take a shot at it?
jelly2m8 JUN 30, 05:22 AM

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Originally posted by Yellow-88:


I could not find any discussion about the factory ackerman angles on the 88.

You won't find any because "Akerman" is not and angle. Ackerman is the principal that the inside steering tire will follow a shorter radius than the outside steering tire. Projected axel centerlines will meet at the same point.




Exactly this 'Ackerman angle' is a made up term for someone wh0 doesn't understand the basic of steering geometry. what a messed up world we now live in.

This can be a great conversation, start with Steering axis inclination, see how that effects things and work from there. No, this isn't your answer, but will set you into the right direction of knowledge

[This message has been edited by jelly2m8 (edited 06-30-2024).]

Yellow-88 JUN 30, 10:38 AM

quote
Originally posted by jelly2m8:
Exactly this 'Ackerman angle' is a made up term for someone wh0 doesn't understand the basic of steering geometry. what a messed up world we now live in.

This can be a great conversation, start with Steering axis inclination, see how that effects things and work from there. No, this isn't your answer, but will set you into the right direction of knowledge




Hi.

To continue ... now that we have a virtual chassis with a suspension system it's time for more terms and concepts. First we need to revisit my description of "roll axis".
In the first ultra simple chassis model with no suspension, I described roll axes as a line between the front and rear centers of mass. With the suspension system added that line runs between the front "roll center" and the rear "roll center". Roll Centers are points in space created by the "geometry" of the suspension system; that's the parts that actually locate and move the components of the chassis. "Steering axis Inclination" is just one of the concepts that determine the location of "roll centers". I'll continue a discussion of that after my "Sunday Afternoon Blues" jam session. Yes ... knowledge is powerful.