koni yellows w/ eibachs vs koni yellow gc 500/400
 

guys i am currently running koni yellows with pettit eibach springs (i think they are simple renamed prokits but not sure though). i am considering upgrading to the gc coilover conversion. i have a few questions: does anyone know what the spring rates are for the eibachs? i am guessing somehting close to 350/250. is going from that spring rate to say 500/400 going to change the ride much? what are the benefits of running a higer spring rate?

has anyone gone from a setup that i am currently running to the ground control coilover kit? is there an improvement? is it worth the $$. tks.

do you open track or autocross? do you use R compounds?

if you just drive on the street, don't bother.

+1

Please look at the damper dyno, if possible. I believe the Koni sports are valved for a medium spring rate. So if you go with stiffer springs, you will be at the upper ranges of damping adjustment for your suspension to work optimally. You must also take into account the stroke length. You would want to utilize all of the stroke length - if you run too stiff a spring, you will utilize less of a stroke length. I suppose damping efficiency would decrease if you don't run a full stroke?

Why are you running stiffer springs anyway? Is there something in particular that you are trying to correct?

Not sure what kind of luck you guys have had but many years back I ran koni's with Eibachs and it was fine for street driving but on the track I had very bad rubing. Wore out fender liners in one event and pulled down my front fender lips. I ordered a set of JIC coilovers soon after and have never had issues and even have my car sitting lower now!

I am looking into the GC and Konis also..any words of wisdom would be great.

I have had both of the setup you mention: Koni/Eibach (which are roughly 360/275 or so), and then Koni GC 500/400.

My honest assessment is that the ride was BETTER with the GC. The Pro-Kit's lower the front alot... too much really... so I ran the Koni's on the highest perch in front, middle perch in the rear to even the car out. I think the spring rate on them just isn't high enough to cope with a lowered car, and as a result, the thing rubbed a bit, and crashed down over bumps or big dips in the road.

The 500/400 GC set up is better because it has enough rate to keep the car up and over such undulations. Spring rate itself isn't the end all be all of ride quality, which owes alot more to shock valving than just spring rate. You'll find that some higher-end coilovers with high rates will actuly ride better than low-rate stock replacement springs and cheap shocks.

I'd recommend the 500/400 GC setup over Pro-kits.

Good info ptrhahn.

I run the H&R springs with Konis. Haven't had any rubbing issues with 255/40/17 on track. Ride height is ~25.5" front.

yeah i dotn ahve anyn rubbing with my current eibach koni setup and its set up same way yours were.
whats the benefit of higher spring rates? body roll?

and tks for the post...very helpful

The nature of Konis is, they don't seem to have a great deal of compression stiffness, and only the rebound is adjustable anyway. The extra rate helps both with body roll and stability, as well as the cars ability to stay off the bump stops over significant undulations.

When I say "rub" I didn't mean the typical wheel fitment rub, so much as crashing down too low over bumps and such.

Higher spring rate = more force to compress a fixed travel distance in your suspension. This translates to less body roll.

Now, dampers have nothing to do with how much your spring compresses. Dampers only affect how long it takes for forces to transfer between corners of your suspension.

Spring rate is what determines the stroke of your suspension. If you have too low a spring rate for your chassis, there will be too much travel - and that's when you hit the bump stops. When you hit a bump stop, all the energy that the spring has up to that point absorbed is immediately released in the collision between the suspension joint and the spring perch. That's when you get what is commonly described as "crash."

So, apparently 360/275 Eibach lowering springs have insufficient stroke or spring rate for our FDs. You may say, hey but stock springs have an even lower spring rate, how come my suspension never crashes with stock? That's because the stock springs aren't lowering springs. They have a longer travel by design.

So, to compensate, you can either have better designed springs (as opposed to cut or poorly designed lowering springs) that will give you the full travel that you seek, and have dampers that are matched to that spring rate. The valving should transfer fore/aft forces in a controllable fashion, such that the limits of adhesion of each individual corner is maximised.

As a car travels through a corner and the suspension is loaded on the inside and unloaded on the outside, you would want the outside to unload as slowly as possible so that you maintain maximum downward force exerted by the weight of the chassis. You want the spring to have large rebound damping. To damp a force means to reduce the force. In this case, you're damping (reducing) the force at which the spring pushes up against the chassis.

There you go, suspension dynamics 101.