66IISS

Hey guys,

I was reading the SCCA 2009 Street Prepared rules last night while trying to come up with a clever way to gain more rear traction in my 1996 fully prepared BSP corvette and I came across this part:

H.Camber kits, also known as camber compensators, may be
installed. These kits consist of either adjustable length arms or
arm mounts that provide a lateral adjustment to the effective
length of a control arm. Alignment outside the factory specifica-
tions is allowed. The following restrictions apply:

So does this mean that something like...

http://www.vbandp.com/detail.aspx?ID=640

Is legal?

My next question is, how much would the "smart struts" from Vette Brakes really help? Just a recap, we have 335 wide rear tires and we are constantly battling oversteer issues, especially with the lightest application of throttle.

The car has a fully prepared engine (to the limit of the rules), 1100 lb/in (i think) vbandp front springs, 680 vbandp rear springs, penske 8300 shocks, offset bushings (about -3 camber front, somewhere around -1.5 to -2 in the rear), not sure on the sway bar size.

Does anybody have the smart struts / any opinion on them? There was one thread from years ago, but there weren't any good comments on it. The search here sucks.

-Brad

66IISS

Nobody's tried the C4 smart struts?

C'mon guys, I realize the C4's are a touch outdated, but they're still fun!
I can still keep up with the C5 Z06, and this car sounds way cooler!

bump for the C4 drivers....

froggy47

Email Doug Gill, scca for legality.

I don't see why they would be disallowed, but my OPINION does not really count for much & never ran an SP car.

But do you want MORE rear neg camber?

I'd think you would be playing with rear toe in?

BrianCunningham

Adjustable a-arms in BSP is a new one on me

As far as I know, rod ends put you in SSM (was SM2)

Moving the inboard mounts moves you from SSM to EM, which the smart stuts do.

I'd like to see the camber curves on the smart struts, as far as I can tell they make the links more parallel to each other, which is great for tire wear, but makes the tire have even MORE camber change.

What we're dealing with on a C4 is that the upper link, the halfshaft, is longer than the camber link, which makes them have POS camber under compression.

RX7 KLR

I would say no. The rules do not allow for the amount of metal content in the bushings to increase - this is the case for every bushing you are allowed to change in SP - and those appear to have a lot of metal and very little bushing material in the ends. Also the VBP seem to include new mounts, no allowance to move/alter attachment points. I would say even if these are in the OE location the would not be legal.

This one from Eckler's looks like it has closer to OE amount of metal in it:


VBP end appears to mostly consist of metal:

RX7 KLR

Try a softer rear spring and some more toe-in.

66IISS

The amount of metal in the bushing is suspect, but that could also be just be a metal flange that's acting as a washer. I'd have to call Vette brakes on that.

As far as the mounts... I think this part of the rule can clarify:

4.The replacement arms or mounts must attach to the original
standard mounting points. All bushings must meet the re-
quirements of 15.8.C. Intermediate mounting points (e.g.
shock/spring mounts) may not be moved or relocated on the
arm, except as incidental to the camber adjustment. The
knuckle/bearing housing/spindle assembly cannot be modi-
fied or replaced.

The way I read in to this is that the new mounts must mount to the OE attatchment points, not the arms themselves as per "or" in the first sentence. This would allow for moving the arm mounting point inward, which seems to be allowed by the first part of the rule which allows for mounts that allow lateral movement.

The bushings are still suspect though.

Also, I'm not positive the rear spring is the problem because the suspensions is hitting the bump stops. I'm not sure what the rear has for toe in, I'm sure it's some. The front has plenty of grip, the turn in is awesome. The rear just likes to pass the front frequently.

66IISS

These are addressing the camber under compression, aren't they? I've noticed in all the pictures of the car that the camber goes positive in compression. The front camber isn't the greatest under compression either as far as I can tell.

RX7 KLR

You are replacing the OE mount, how is that not altering it? You are also changing the geometry. I say no way.

Shorten the stops, lift the rear, there are a number of options. Having the car sitting on the ground is not always better.

66IISS

There are lots of ways to skin a cat, I'm not arguing that at all. We've got a test and tune day coming up of which I'm going to do everything possible to fix the issue, these camber links caught just my eye and got me thinking. It's a new rule this year and is open to interpretation as it seems a touch open ended.

The way I'm reading it is that the mounts don't need to be OE, they just need to attach to the OE points, and then where the arm attaches to the mount can be moved, as per the first section of the rule that says the new mounts can provide lateral adjustment that only effects the effective length of the arm.

RX7 KLR

While they may look the same, if they change the vertical location of the end of the arm you are changing the geometry.

turbotim23

not sure about rules I do know the smart struts are also adjustable up or down on the inward mount. If legal how would this adjustment help for autocross? The main reason I didn't buy them, I wasn't sure my 3" borla exhaust would fit and didn't want to have to cut center of smart strut mounting bracket.

CorvetteZ51Racer

This may be a moot point, but TECHNICALLY speaking the inboard vertical position of the OEM strut rod changes ANY time you change the camber setting...just watch the movement as you turn the eccentric. So if you're going to be technical about changing the geometry by a vertical change in the inboard end of the strut rod....

Can one legitimately argue that while the smart struts vertical position may change, if it is still within the range of vertical positions made possible by turning the eccentric then you have not really changed the OEM suspension geometry?

grantar2

Realize this thread is far out of date, but if you haven't found the fix, I have to ask if you followed the common wisdom of lowering the rear end ride height. If you did, start moving it back up some and you will reduce your oversteer.

MSR

since this thread floated back up...

that's only one factor that determines the camber curve. on my '96, in the meat of the travel it uses on track, the halfshaft is past horizontal while the lower control arm is short of horizontal, so i get more negative camber with bump. i think even in the early '80s gm engineers knew not to make a backwards camber curve on the rear suspension of their flagship car! if anything, the camber curve is pretty steep, which has the negative side effect of introducing jacking. this is especially true of the early C4, but still true on my '96.

i had tried the DRM brackets, which lower the roll center and decrease jacking (by lowering the pickup points), but also make it so the rears don't gain as much negative camber in bump. i didn't think about it long enough to realize i'd have to make changes to take advantage of that, so i slowed down (and consequently took them off). since then i've put them back on, increased spring rate (now that it jacks less), and increased the static negative camber, and it is better/faster overall. i perceive it's faster because it's more consistent in its cornering balance/behavior, not because there's more rear grip, which is consistent with a reduction in jacking.

also not true. the slots for the bolts in the brackets are horizontal. the edges which the eccentrics leverage against are vertical. this means the eccentrics' centerlines move both horizontally and vertically as they're adjusted, but the bolt itself only translates horizontally.

this is all BSP legality aside, i just wanted to clear up how the C4 camber curve and stock arm mounts behave.

-michael