I finally got around to installing Smart Struts and I wanted to understand the potential impact on the vehicle. I suspect that some will say, it is the "seat of the pants" that counts and I can't disagree with that. However, some may find this analysis interesting.

As you all already know, Greenwood recommends that the pivot for the inner strut rod be lowered 1/2” lower than OEM or 1” below the differential bottom or bolt surface. The relationship between axle position and camber degrees is a sigmoidal polynomial function. Using 13 points of raw data provided by other CF members, a polynomial equation correlates axle position with camber degrees to an accuracy of 99.38%. A linear equation correlates axle position with camber degrees to an accuracy of 99.26% so a linear equation was used to construct this table (slide rule accuracy).

________|------------Camber Degrees----------
________|OEM_____--Smart Strut Setting--
Axle Pos.__0.0"____-0.5"____-1.0"___-1.5"
+2.5".......-2.7.......-2.5.......-2.3.......-2.1
+2.0".......-2.4.......-2.2.......-2.0.......-1.9
+1.5".......-2.0.......-1.9.......-1.8.......-1.6
+1.0".......-1.7.......-1.6.......-1.5.......-1.4
+0.5".......-1.3.......-1.3.......-1.3.......-1.2
0.00".......-1.0........-1.0.......-1.0.......-1.0
-0.5".......-0.7........-0.7.......-0.7.......-0.8
-1.0"........-0.3.......-0.4.......-0.5.......-0.6
-1.5"........0.0........-0.1.......-0.2.......-0.4
-2.0". .......0.4.........0.2........0.0.......-0.2
-2.5"........0.7.........0.5........0.3.. .......0.1

Axle Position: At rest is 0 inches. Axle movement up relative to center of vehicle, or spring compression, is positive position in inches.
Camber: Negative camber, in degrees, is top of tire tilted toward center of vehicle.

 

Smart Struts are a good idea for drag racing, but not for handling. As the car squats during launch you don't want neg camber so Smart struts are good. But when cornering you do want camber gain on the outside wheel to counter body lean.

Edit: I'm having a hard time figuring your table. Is the first column with no smart struts?

 

Thing is, modern tires just don't require as much neg camber gain as did those of 40+ years ago, while wider tires tend to work better with less camber gain. So, given that alone, there's plenty of reason to consider reducing rear camber gain in the C3 IRS, and more so in the C2. That said, eliminating camber gain altogether should be left to those setting up specifically for drag racing.

FWIW, I've spent a good number of hours over the years studying the dynamic geometry of the C2/C3 IRS, and the maths I've done back up John Greenwood's recommendation to lower the inner camber strut links -1/2" below the stock C3 height (relative to the diff) as the default setup for most any C2/C3 on modern tires; save for drag racing. I'd highly suggest using this -1/2" adjustment as the baseline setting, and if not satisfyed to then, and only then, try subtle steps (+0.25") to see what the stopwatch, tire temps and driver's backside indicate works best. Without such testing to prove a different setting actually helps (and it might on a given day/circuit), I'd leave it be at -1/2".

But, while we're on the subject, among other determining factors which might prove a different setting are those of rear spring rate, total rear roll stiffness, weight distribution, CG height, power/weight ratio, gearing, available traction, conditions, the circuit in question and driver preferences. So as to not get completely bogged down in theory here, the general rule of thumb is that the more dependent on straightline acceleration are better lap ET's, the less rear camber gain will typically be desired; while the more time spent in long corners relative to straights, the more important will be optimum camber gain in bump/roll. Sorry, there's no one-size-fits-all demon tweek.

Further, duly noting that static ride height affects not only the camber curves, but track variation and toe-steer curves as well, I've also concluded that Greenwood's recommendation that static rear ride be steup to have the inner U's 1/2" above the outers again appears spot on. And, combining these two adjustments (both inner strut and diff heights) significantly reduces rear track change in bump/squat travel (that's when it matters most), tho static diff height affects this somewhat more than subtle camber gain adjustments.

Lastly, since no single suspension property lives in a bubble, it's worth pointing out that lowering the inner strut links not only reduces camber gain (by function of lengthening the virtual swing arms), but also lowers the rear RC and reduces jacking, among other things. Yes, for the sake of argument (and IMOE some can't let it pass), there are downsides to doing this, but they are substantially outweighed by the benefits. Hope that helps.


TSW

 

As a follow up, I'm extrapolating that the static ride height relative to the OP's findings is apparently with the half-shafts at or near level, and attribute discrepancies between his results and my own calculations to be more than likely due to a margin of error in measuring and entering vital data points. In any event, IC's, RC's, camber gain, track variation, toe-steer, roll axis, roll couple distribution, roll angle, jacking, etc. can most certainly be calculated with high precision, if you understand the maths involved, but will always be subject to how accurate is the input as mentioned above.