Ground Control Koni Performance

[sprintamx]

I've been running a GC Koni sport adjustable setup for about two years now. This is the full kit with GC camber plates and trust bar. I opted to go with 375lb front / 350lb rear to keep handling more street oriented and somewhat balanced as the car was set up in the factory. I dropped ride height about one inch front and rear. Alignment specs are not aggressive. The only other suspension changes are rear subframe bushing inserts and differential bushing inserts.


I'd like to know what others' experience has been with the Konis and how you like or don't like the performance--specifically on the street.


On track, the setup works relatively well, but I've struggled to find a reasonable ride on the street. After more than a year of fiddling, I've settled on about one turn from full soft (rebound only) on the fronts, and (think) the middle rebound setting on the rear. It's hard to adjust the rears when installed. Ok, it's a pain in the a---


Like most performance oriented suspensions, there is some compromise here, but I've had an almost impossible time to find a balance between good control and managing bumps and bad pavement. Too stiff and you lose your teeth, too soft and the car is a basket ball. In the middle, and the car is relatively composed but a bump or quick series of bad pavement and the rear end is constantly kicking out. And, with the inherent valving and limited adjustability, I don't think there's anything else I can with the rear shocks themselves.


So, I'm interested to know what others who are running Konis have managed to sort out. Ride height? Spring choices? Other bits? Do you have a good and compliant ride on the street, or are you putting up with hopping rear end?


Thanks for your feedback.


Aaron

[renfield90]

My autocross setup was the TRD springs on Koni sports. I don't know for sure the spring rates of the TRD springs but they are probably close to yours and it was a similar drop (0.75-1 inch).

Obviously had different goals than the track but I settled on 1.25 turns from full soft on the front and 0.5 turns from full soft on the rear. 1.5 turns on the front was too much and created a lot of turn in push especially in slaloms. For the rear I felt 0.5 turns was already pushing it in terms of too much damping, any more and I would start adding inside wheel spin at corner exit. Throw on my daily drive set of tires and 0.5 would be too much and leave me peeling out every time I made a sharp right turn at an intersection.

My one gripe with the Koni sports is you can't adjust compression and their shock philosophy tends to give you shocks with lower compression than a lot of their competitors. For not a ton of money Pro Parts can revalve you with DA to help with some of this.

For street settings I would soften front rebound by a half turn and soften rear rebound by a quarter turn (that is, 0.25 turns from full soft in the rear). I do not recommend running Konis at full soft or full hard in case you hit a really bad bump, the adjuster could get locked there and require service. If you're having oversteer issues on the street and your rears are at the "middle" setting try backing them way down.

[sprintamx]

Thanks for your thoughts.


With the GC Koni rear shocks, there are three adjustment settings for rebound, for 20%, 50% or 100% of the rebound range. Adjustments are made by depressing a button on top of the shock body while rotating the piston or shock body. So there's a fairly limited range of adjustment.


I wouldn't describe my issues as oversteer, but that the car just will not stay composed over significant bumps or dips. At speed, the rear constantly wants to kick out, and the front will tend to also with really bad pavement.


Thanks.

[ryoma]

what is your alignment? bad toe in the rear might be a potential cause of your issue.

[sprintamx]

It's been some time since I had the car aligned, but static toe was set to 1/16 total toe in.


Thanks.

[ryoma]

did you get an alignment after lowering your car or after installing your bushings? since you have stated it has been some time since an alignment, maybe it is time for another one. I think there is a consensus that you should get an alignment once every year or two, and especially after messing with any part of your suspension including subframe. however, I am not a suspension expert and you should probably wait until someone more knowledgeable chimes in

[sprintamx]

I aligned the car after installing the Konis with the lowered height.












After reading the MotoIQ review and analysis of the Twins' suspension--they conclude that the car likely toes-in under compression--I wonder whether the Koni valving and spring rates struggle to keep the rear under control during significant upset. Pure guesswork on that conclusion. And, yes, it's likely time for a fresh alignment.

[Devil 86]

I'm running Koni yellows with RCE Tarmac springs and I ride 1 turn from full soft all the way around. Spring rates are 280 in front 290 in the rear and it's pretty damn stiff even at full soft. My damper adjustments vary with each autox course. There's a touge that I like to run that's extremely bumpy and makes the rear end kick out a bit even at full soft so I had to change my driving style accordingly. I think I might buy the racesenge rear top mounts that add 2" of shock travel to combat this issue

[sprintamx]

Can you guys describe the mechanical process for adjusting your rear shocks? Are you removing them from the car? Is there an adjustment button you depress to change the setting?


Thanks.

[Devil 86]

There's a knob on the top mount that you just turn. All u have to do is open your trunk and turn the knob. Your situation may differ because u have the coilovers

[sprintamx]

The coilover version adjustment process is different, and definitely more involved.

Thanks.

[renfield90]

Originally Posted by sprintamx

Thanks for your thoughts.


With the GC Koni rear shocks, there are three adjustment settings for rebound, for 20%, 50% or 100% of the rebound range. Adjustments are made by depressing a button on top of the shock body while rotating the piston or shock body. So there's a fairly limited range of adjustment.


I wouldn't describe my issues as oversteer, but that the car just will not stay composed over significant bumps or dips. At speed, the rear constantly wants to kick out, and the front will tend to also with really bad pavement.


Thanks.

Hmm, that's a very unfortunate set of adjustments. I'd never run Konis at 100% due to the risk of damage from bottoming out, so that really leaves you with two adjustments. Did you get shock dynos by chance?

My vote is you try 20% in the rear. But IMO, I think GC got the shocks wrong. The right answer* might be 35% but you have no way to adjust it there. GC normally provides some pretty good stuff so this is a little disappointing to hear.



*Assuming, of course, that compression is correct. Normally Konis are fairly low on compression but GC may have upped it, which could definitely cause issues over bumps. No way to know without a dyno.

[sprintamx]

No shock dynos with the GC Konis, and I haven't done any independently.

GC states that they spec'd the BRZ/FRS shocks specifically from Koni, and are therefore different than a standard Koni yellow. I don't have any experience with the standards, but I think that the custom valving has more compression.

Full soft on the rear rebound adjustment is ridiculous. Full stiff is great on track, but annoying before too long on the street.

GC wants to pair these shocks with heavier springs than I opted for, but I think that's still for a more track-oriented focus and may or may not smooth out the performance on rough street pavement. I've found a relatively happy medium at the middle rebound setting on the rears, and I think that's the best I can accomplish with this particular setup. I think I'm also forced to conclude that GC is off with their valving specs for this equipment. Beautiful engineering for what they made, but other manufacturers seem to have developed more flexible options.

[Hyper4mance2k]

the first thing you should do is get the higher spring rate in the rear. Second, if you're picking up an inside tire, I'm guessing you have a big rear sway bar. Try going back to stock.
The TRD Springs are rebranded Eibach Pro-kit, and no where near close to the rates you're running. Theure 3.6k/4.9k and you're running closer to 6.4k/6.2k.
This car prefers a stiffer rear spring due to different motion ratios between the front and rear. You may want to call a well known tuner here and get some spring rate advice, then call ground control back and let them know they made a poor recoomedation. My car runs 4.4k/5.3k