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Restoring Camber Curve... Different Application.... Help!

4
4
Exp. Type
Drag Strip
Exp. Level
20+ Years
South Coast, Massachusetts
Ok here we go..Drag race application striving for 0 camber at rest and thru some bump and extension, lowered S197 w/ ford 5300RA springs, FCA's are now virtually horizontal , (1.5* downhill from k mem to BJ ) originally when lowered had way to much neg camber, CC plates extended the tire too far out of the wheel well, and refuse to use those skinny camber bolts at the strut/ spindle. Sooo, after removing CC plates, I measured how much was needed to shorten the LCA's to get a 0 camber or very close to it, bought a set of used low mileage arms and shortened them 13/16" . while I was at it, installed New Prothane bushing kits and put it together, shortened the tie rods and ends (stock) proportionally. Now I have 0 * / .25* at ride height, so my ruler didn't lie .... but now I'm at a camber change rate i don't like and bumpsteer is not good. My question is anyone out there with an analysis program or familiar with the S197 suspension plotting to get this Camber Curve in the Ball park? I'm considering and have extended Ball Joints, X-11's at + 1/2" or Forgetrues at +7/8" .. and have a bumpsteer kit ready to go,. Any final Camber fine tuning will be accomplished by Using the Ford S197 full size camber bolt correction Kit # M-3B236A ... TIA Steve

KIMG0267.JPG
 
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Norm Peterson

Corner Barstool Sitter
939
709
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
MacStrut suspension geometry inherently forces significant greater amounts of camber change as ride height varies from bump to rebound than any decent short-long arm suspension.

About the best you can do is find a geometry (control arm + strut inclination) and static camber setting that minimizes it over your expected range of suspension travel.

Keep in mind that I'm trying to visualize this as I go for now, but I suspect that you're going to be much more interested in the rebound-travel side, given that the nose ought to be staying at or above static ride height for most of your run.

Initially, that tells me that you might want to set camber at zero at some amount of "nose rise" and find a geometry that minimizes camber gain between static and that nose rise height, even if it makes for greater camber gain elsewhere over the range of suspension travel. Generally, that means a slight amount of negative camber at static ride height.

At least with your stick-axle car, you'll probably be running enough rear sta-bar to keep the car somewhat closer to level (in roll) and avoid having a front tire going way off into positive camber if things get squirrely for any reason.

Geometrically, camber change is linked to the location of the front view instant center - a virtual point in space defined by the LCA inclination and a construction line drawn through the upper strut mount at 90° to the strut axis. LCA inclination appears to have a greater effect than strut inclination (C_C camber or camber bolt settings) here.

I think lowering both of the LCA chassis-side pivots will slow down the camber change during nose rise, and since you're not cornering it won't much matter that bump-side camber gain gets hosed as far as cornering grip is concerned. The 2D spreadsheet I'm working with looks like camber can be held between -0.6° at static and about +0.6° at 2.5" front suspension rebound travel - with your shortened LCAs and a little over 1.5" downward relocation of the LCA chassis-side pivots. I haven't looked into what impact that would have on bumpsteer except to suspect that you'd want to relocate the rack downward as well.

Right now, I'm seeing your camber varying between 0.25 at static and more than +2° at 2.5" front suspension rebound. You'll want to experiment with your static setting - at full nose rise there isn't going to be much load on the front tires, so you can probably run a little less static than -0.6° and let the camber at +2.5" run a bit more than +0.6°. It'll be a balancing act that will take some test & tune time.

Just so you know, I have not reviewed this spreadsheet against any other suspension geometry software. But I think the math for this part of it is OK.


Norm
 
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Norm Peterson

Corner Barstool Sitter
939
709
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
On further thought, the above suggestions would probably hose the geometry for corner-carving.

The front geometric roll center would be a few inches lower under all ride heights. This means more roll, but also a rearward shift in the car's overall roll resistance (making any rear antiroll bars slightly more effective at re-planting the RR tire).


Norm
 
4
4
Exp. Type
Drag Strip
Exp. Level
20+ Years
South Coast, Massachusetts
Thanks for taking the time to reply.
I know this situation is kinda " thinking out of the box" .... The instant center I understand after years of plotting 4 and 3 link rear suspensions, vs CG of the car, but didn't know where to pick up the angles for the Mac strut suspensions, something new to me. and yes we strive for our ideal camber / toe settings at ride height during the run. This being a lower classed, low horsepower combination, the changes in ride height won't be that severe vs a car that pulls the wheels of the ground. The car is equipped with full Cobra Jet rear suspension that includes an Anti Roll Bar so that roll shouldn't be an issue. I follow your analysis and remedy, however, the car is in a category (classification) that prohibits the use of an aftermarket K member or LCA's and cannot relocate the Rack or LCA mounting points at the K member so I have to work with what I have.
( Question , based on this information, if Extended Ball Joints were installed, during extension, this would amplify the problem, yes or no? )

So, your summation, " Right now, I'm seeing your camber varying between 0.25 at static and more than +2° at 2.5" front suspension rebound. You'll want to experiment with your static setting - at full nose rise there isn't going to be much load on the front tires, so you can probably run a little less static than -0.6° and let the camber at +2.5" run a bit more than +0.6°. It'll be a balancing act that will take some test & tune time." is basically what I'll be working with, and tuning the bump steer kit, pending any other thoughts You may have.
Thanks again...

"
 

Norm Peterson

Corner Barstool Sitter
939
709
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
What about custom steering knuckles? Dropping the height of the spindle and the lug that the strut attaches to height or raising the balljoint pad ought to raise the wheel end of the LCA inclination relative to the chassis end for similar effect.

Short struts (with appropriate springs) should also drop the chassis relative to the balljoints.

Basically, I'm trying to get your LCAs running downhill from balljoint to chassis-side pickup.


Norm
 
Last edited:

Norm Peterson

Corner Barstool Sitter
939
709
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
I'm afraid I didn't type everything the way I had it in mind earlier this afternoon. I missed the important part of one of those options and typed what wouldn't change LCA inclination.

This is about the best I can do . . .

Possible knuckle mods.jpg


Norm
 
Last edited:

Norm Peterson

Corner Barstool Sitter
939
709
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
Interesting,,, short of using custom spindles, economics tell me to dig out my spare K -Member w/ LCA's and do some experimenting. Or Shim the K frame down in the car since the towers / strut/ springs/ spindles support the weight. ?
Shimming the K-member down should accomplish the same thing geometry-wise, without affecting tierod inclination relative to LCA inclination very much (they probably are NOT exactly parallel anyway).

Motor mounts/motor installed height/driveshaft angles and header clearances come to mind.


Norm
 

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