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SCCA F-Street Setup. What's Everyone Done so Far?

qtrracer

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I guess I don't see how -2.5º is too much camber up front for the suspension (unless you are talking per the OEM slotting procedure) when we are still seeing gobs of wear at about 2º or more taper from inside to outside edge.
It was the OEM "slotting" but with an aftermarket strut. This procedure while gaining static camber, also throws off the KPI by a bunch. The s550's Bimmer type front suspension should be worked on with this in mind. By going to C/C plates, we can move the KPI back to where it belongs and get the proper static camber given dynamic camber gain the suspension produces. Hence, why I'm back to -2.1* with C/C plates. Still testing so this setting may change further positive.

Me, after this year I'm hoping to have a CAM car built and ready to go for a shakedown season.
My s550 is not my intended A/X open track car. An interim solution. My '86 Mustang was designed and built per SCCA CAM specs - not for nationals, but more GoodGuys, Ultimate Street Car and HPDE/PDX events. Should be ready for next season but if not, back to the s550 - in STP.:)
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qtrracer

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But it's FS and camber plates aren't legal.
We were discussing why some guys moving from FS to another class and why. I'm going to STP. Hence the CC plates.

KPI (or SAI) doesn't change when you slot the struts, but scrub radius does.
Yes it does. Confirmed by MM. When we slot the strut, the angle of the spindle changes relative to the strut - changing camber (+/-) depending on which way you move the spindle.

Why would scrub change? We didn't move the wheel center-line in or out relative to the stock position. If we added spacers (out) or more wheel backspacing (in), then scrub would change. By slotting the strut we don't do either.
 

DickR

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Question: What are the negatives with the S550 suspension of changing KPI when slotting to get some more negative camber? Both for autocross and for lots of highway driving.

Thanks!
 

Norm Peterson

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Why would scrub change? We didn't move the wheel center-line in or out relative to the stock position. If we added spacers (out) or more wheel backspacing (in), then scrub would change. By slotting the strut we don't do either.
There's a third way scrub radius can be changed, and that's when the wheel is essentially pivoted about one of the strut to knuckle fasteners. Spacers and offsets move the wheel translationally, but that's not the only way that scrub radius is affected.

Adding negative camber rotates the wheel plane as seen in front view such that the wheel center at the contact patch moves outward, either because the lower hole is slotted and everything below the upper fastener moves outward or because the upper hole is slotted and it's everything below the lower hole that moves outward.

That's the answer based on geometry alone.

The geometry & compliance model might not be quite as bad given that the distribution of corner weight over the contact patch will tend to be a little higher on the inside (and a little lower on the outside) due to the camber change.

I'm not even going to try to guess which effect dominates in a straight line, let alone in a corner where the tread can move relative to the wheel . . . on the order of a whole inch.


Norm
 

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dontlifttoshift

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Yes it does. Confirmed by MM. When we slot the strut, the angle of the spindle changes relative to the strut - changing camber (+/-) depending on which way you move the spindle.

Why would scrub change? We didn't move the wheel center-line in or out relative to the stock position. If we added spacers (out) or more wheel backspacing (in), then scrub would change. By slotting the strut we don't do either.
KPI is the straight line through the lower ball joint and the upper bearing on a McStrut. No matter how much you slot the struts, the ball joint and the upper bearing don't move so KPI stays the same. Like Norm said, that is exactly why scrub changes when you adjust camber at the strut to spindle interface. KPI stays the same but the centerline of the tire moves when you change camber.

When you adjust camber with camber plates, scrub radius stays the same but KPI changes. So does your roll center.
 

qtrracer

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KPI is the straight line through the lower ball joint and the upper bearing on a McStrut. No matter how much you slot the struts, the ball joint and the upper bearing don't move so KPI stays the same. Like Norm said, that is exactly why scrub changes when you adjust camber at the strut to spindle interface. KPI stays the same but the centerline of the tire moves when you change camber.

When you adjust camber with camber plates, scrub radius stays the same but KPI changes. So does your roll center.
Agreed to a point. Recall that this front suspension is similar in design to the Bimmer strut - two lower ball joints. This creates a "virtual" steering pivot - not easy to calculate. Setting that aside, the KPI measurement assumes a given angle to the hub mounting face - included angle. Slotting the strut changes this angle. By how much I don't know. But the change has an impact which likely cascades throughout the design. If you both slot the strut and use CC plates to achieve a given static camber, now you have potential extremes on both camber and "KPI", and a scrub change.

This front suspension design does not need those extremes to achieve maximum grip. There is adequate designed in dynamic camber so a lot of static camber is unnecessary. The suspension also has enough static caster. But fixing caster build tolerances is doable with after market CC plates.

Some empirical observations. I went from about -2.5* static camber using the slotting method to -2.1* with CC plates. I put the spindle back to the original spec. Still ran 1/8" toe-out. Same stock wheels and MPSS tires; same shock settings. Noticeable difference in the way the car turned in, at mid corner and exit. Much easier to drive which increased confidence and predictability. The only changes beyond above were the course layout and weather was colder; venue was the same.
 

dontlifttoshift

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Setting that aside, the KPI measurement assumes a given angle to the hub mounting face - included angle.
Can you cite a source for that information. Nothing I have ever read requires the angle or even the position of the hub for SAI.....regardless of number of ball joints.
 

destoups

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I can hardly wait to see how well the 10A behaves in regard to autocross relevant shifting control and speed. I'm particularly interested in whether this statement in the owner manual means what the words "seem" to say.
Dick, I have a 10A Ecoboost. The car holds gear fine as long as you're engaging with the paddles and the little number indicating gear is lit. If you're in D you can use the paddles but it resumes automatic up and downshifts after a few seconds. In S, it seems to be persistent as long as you use the paddle to select a gear right away (otherwise assumes you just overshot D on the shifter).

Haven't had a chance to do much except launch it. Which was awesome.

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DickR

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Dick, I have a 10A Ecoboost. The car holds gear fine as long as you're engaging with the paddles and the little number indicating gear is lit. If you're in D you can use the paddles but it resumes automatic up and downshifts after a few seconds. In S, it seems to be persistent as long as you use the paddle to select a gear right away (otherwise assumes you just overshot D on the shifter).

Haven't had a chance to do much except launch it. Which was awesome.

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Great. Did you get MagneRide?

Do you plan on autocrossing it or to compare it with Mark's Camaro to see which is faster?

My 18 GTPP 10A with MagneRide is due in early January (build week 12/18). Mine will be Ruby Red again.
 

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DickR

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destoups

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Yep, will prep it and see which wins. If EB is faster I won't let Mark near it.

Still have my Camaro down in Georgia, too, so covered either way!

No Magneride -- none on the ground in the NW, and with Konis so cheap it didn't seem worth it to wait.

As far as I can tell after a few hundred miles, it holds both second and third gears at redline without an upshift. Not sure of what issue you see in the owners manual text — that it won't?
 

DickR

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Yep, will prep it and see which wins. If EB is faster I won't let Mark near it.

Still have my Camaro down in Georgia, too, so covered either way!

No Magneride -- none on the ground in the NW, and with Konis so cheap it didn't seem worth it to wait.

As far as I can tell after a few hundred miles, it holds both second and third gears at redline without an upshift. Not sure of what issue you see in the owners manual text — that it won't?
The bolded words below, if accurate, indicate that in S with selectshift activated by paddle use the trans will upshift at redline IF at full throttle.

SelectShift Automatic™ Transmission
This feature gives you the ability to change gears up or down as desired.
As long as the engine speed does not exceed the maximum allowable limit, downshifts are allowed. SelectShift automatically downshifts at low engine speeds in order to prevent engine stalls.
Note: Engine damage may occur if you maintain excessive engine revving without shifting.
In drive (D) SelectShift automatically upshifts at the optimal max engine speed, regardless of accelerator pedal travel.
In sport (S) mode SelectShift does not automatically upshift, even if the engine is approaching the RPM limit, unless the accelerator pedal is at full travel.
That could be handy for those situations where you would like to go up one gear automatically but have it hold that gear until you manually downshift as needed. Especially given how "short" the 10A second is.

I have no idea whether it actually does that.

See also for how the trans is "supposed" to exit manual mode in S.

SelectShift in sport (S):
Provides a permanent manual gear selection where full control of gear selection is required.
To exit SelectShift mode shift the transmission into another gear, for example, drive (D) or holding the (+) paddle for 1 second.
Did you get a drive mode version (i.e. big screen)?
 

destoups

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Ah, I see what you mean. In Sport automatic mode, yes, the car does seem to hold the next gear at less than full throttle. Full test will have to wait for dry pavement (that is, April).

It also does terrific smooth little downshifts when you trail brake.

Mine's a no-options cheapie, just PP and auto.
 

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Nice to see you post on here again, Des. Nice looking car!
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