Question for CSG, RCE and other suspension gurus:
I recently installed 'motorsport-oriented' coilovers with Eibach Race springs: 500 lbs/in F, 450 lbs/in R. I have the TRD front sway, OEM rear, and got the ride height to about where it was with RCE Tarmacs and B8s. In fact I could not quite get the front as low as it was with the Tarmacs and B8s; the 6 inch long springs w/ no helpers would not remain captive at full droop if I went that low. So the front is maybe 7 - 10 mm higher than it was. There is now about a 5 mm rake F to R, whereas with the Tarmacs I measured a 15 mm F to R rake. I also have Ground Control top-mounted camber plates and their rear top hats that allow the shock shaft to extend about an inch higher.
I find now that the suspension soaks up bumps and broken/patched pavement incredibly well. I hear such pavement imperfections more than feel them now. And it corners very flat, as far as I can tell by street driving. I've yet to try this set-up at an auto-x or track day. I would say overall this set-up is the most comfortable suspension I've had on this car by far. I've had OEM, TRD springs and sways w/ OEM shocks, the RCE Tarmacs and B8s, and now this.
What's odd is that on relatively smooth pavement, I sometimes but not always get a bobbing or jiggling at the nose. They're small oscillations, and it kind of reminds me of driving an older 911 with stock suspension. I say relatively smooth, because in this part of GA there is no completely flat and smooth pavement. It's hilly around here, and they seem to have paved the roads disrupting the natural topography as little as possible, so there are always some undulations and ripples, even in newly laid asphalt.
But I seem only to get this jiggling or bobbing when the suspension is not being worked very hard. Any ideas on what could be causing this?
A couple of possibilities that came to mind are:
- Engine and trans are moving around on soft OEM mounts out-of-phase with suspension?
- Front suspension pivot bolts need to be loosened and re-torqued? I used to have adjustable F LCAs on the car and put OEM back on at the same time I installed the coilovers, along with adjustable R LCAs. I did play around with the ride height after initially torque-ing the LCAs down.
- I need to lower the car more? The drop currently is very mild, probably 15 - 20 mm lower than stock, and the spring perches are sitting in the upper 1/3 to 1/4 of available thread on the shock bodies. I have tons of available compression travel but not much droop: around 25 mm in F and 30 mm in rear.
This is my first go with a 'motorsports-oriented' coilover on this or any previous car. All my previous aftermarket suspensions were in the vein of Eibach lowering springs and Bilsteins, or PSS9's. I've never dealt with such high spring rates before. Is this kind of bobbing/jiggliness something to be expected with 500 lb/in springs?
Thanks for any input you guys have!