Quote:
Originally Posted by H1C
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! |
Quote:
Originally Posted by Racecomp Engineering
This sounds very much like many motorsports oriented coilovers.
Great ride over big bumps and a bit jiggly over relatively smooth pavement. This happens with a coilover that has a lot of low speed compression damping and gas pressure with a very digressive or flat high speed compression.
Reducing gas pressure would help but may affect performance. Do you know what your adjuster controls (i.e. bleed or preload)? Got a shock dyno?
As for your ride height, why not use helpers? I basically always recommend them, and they're even more useful with springs as stiff as yours if you want to get the ride height right.
- Andrew
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Thought I'd provide an update on this front-end bobbing/jiggliness with my MCS 1-way non-remotes, in case someone else with motorsport-type dampers encounters a similar issue:
I wound up removing all of the forward rake by lowering the rear 6 mm, because I've been finding the car too loose at auto-x in transitions and on corner exit. I found this to be the case even with a front-biased spring setup, and after adding a bigger front swaybar (replaced the TRD with the Perrin 22 mm set on stiff).
To my surprise, the zero rake made an already very good ride noticeably better. The car breathes with the road now, and rides flat over long stretches of bumpy and broken pavement. And those sections of local roads that used the get the nose bobbing -- no more. Not completely, but I'd say almost. And whereas the nose used to bob up and down continuously over these sections, now the front and rear feel like they're breathing simultaneously with the undulations. A couple of oscillations and then it settles, whereas before it was continuous bobbing at the nose. I'm not sure if this is what flat ride feels like, but I can't believe how calm the car is now over these sections.
I wouldn't have guessed that the ride could be so sensitive to a small forward rake, but apparently in my case, with my setup, it is. I'm looking forward to auto-xing with zero rake this weekend in our pretty bumpy local lot. I'm hoping and expecting that the rear will be more settled, and that the car will overall maintain more grip over the bumpy sections of the lot.