GC's/Konis or Pro Kits/Illuminas?

[khendriksma1]

I have the opportunity to buy a slightly used set of Ground Control coilovers with Koni yellow adjustable shocks for a very good price. The current spring rates are 450F/190R. I have a 2g FWD car that is mainly street-driven with the chance of a few trips to the track. I am looking for something that will lower the car up to 1.5", handle/ride good, and reduce the rear squat on launch.

Do you think this setup will ride OK and not be bouncy or should I go with something like a Pro-Kit/Illumina setup (or something along those lines? Do the GC spring rates seem right to you for a FWD? I would have thought that for a FWD you would want a little stiffer spring in the rear and maybe a less stiff spring in the front. Anyway, mainly I am curious about how you think the GC/Konis will ride and which setup you think would be the best for my situation.

Kevin

 

[jtmcinder]

Those are crazy spring-rates, especially for FWD. You want to keep the front relatively soft (with weight transferring at the rear in corners), so you actually have some front grip.

With that said, I'd get the GC/Koni set-up, since it not only is adjustable in height, but the Konis are much shorter than Illuminas. Then I would start looking for some used 400# rear springs.

- Jtoby

 

[khendriksma1]

So, in your opinion, what would be the best setup for limited track use(out of these three).

1. GC/Koni coilovers (with 450F/300R spring rates?)
2. Tokico Illumina Kit (w/ springs)
3. KYB AGX with RS-R 1.5" lowering springs

I already have the RS-R springs.

What do you think? I guess I am not convinced that the GS's are the right thing for me... mostly street driving, a few trips to the track, not auto-xing.

By the way, the GC/Koni setup that I have the opportunity to buy is $375 for everything.

Kevin

 

[khendriksma1]

OK, I found out that the rear springs are actually 250lb springs, not 190lb.

 

[jtmcinder]

$375 for Konis and GCs? Grab it! Even if the Konis need to be rebuilt, you've saved several hundred.

You haven't mentioned sway-bars, so I'll assume that they are stock. If so, you really want rear rates above GC's suggestion. 350 minimum, with 450 fronts, and I'd seriously consider 375 or 400. Yeah, 400 is a tad more for autoXing than road racing, but I'd rather be loose and be able to get back on it than push. If running 400s in the rear freaks you out, then get just a rear sway-bar and run 350s.

Oh, and you don't want to go any lower with regard to the front spring-rates or else you won't be able to lower the car enough to get some real front camber (even with Konis). Since you seem to be good at finding deals, I'd be looking for 500-550 for the front and 400-475 for the rear.

- Jtoby

 

[khendriksma1]

Well, I found out that the rears are actually 250 lb spring rate.

What do you think will be less "bouncy"? The GC/Koni setup or loweing springs with adjustable shocks?

 

[jtmcinder]

You always reduce bounciness by upping the spring rates and the amount of damping, especially the rebound. So if this is THE issue, then this argues for the GC/Koni set up, since the springs are higher in rate and Koni yellows have most rebound damping (when set to full stiff).

Note that I said that Koni yellows have more rebound damping than Illuminas or AGXs; I did not say that Koni yellows have more compression damping.

The reason I keep harping on getting higher rear spring rates to go with the 450 fronts (in the GC kit) is that 450/250 will understeer like you won't believe, especially at autoXing speeds. I apologize profusely if this information is not on interest.

- Jtoby

 

[khendriksma1]

OK, so what do I gain with the Koni Yellows haveing more rebound damping thatn other brands but not more compression damping. Would you be able to tell me what the pros or cons are of each type?

Your information is useful so far although I don't plan on auto-xing with the car. Mostly street driving with the possibility of a few trips each season to the drag strip.

Kevin

 

[jtmcinder]

Here's the deal on compression vs rebound damping in two pieces.

With regard to what people mean by "how does the car ride?" the key is having low high-speed compression damping (HSC). HSC is the force the shock produces when the shaft is pushed in fast, as what happens when you hit a bump. The lower the HSC, the less the shock resists this and the less the car (and occupants) feel the bump.

With regard to serious handling performance, such as when autoXing, the key is having lots of low-speed rebound damping (LSR). When you make a fast transition, the shocks on the side that is now being unloaded (i.e., the shocks on the inside of the corner) are being forced to extend by the energy stored in the springs. Weight will transfer faster and the car will "hunker down" if you don't allow this to happen. The extension of shocks due to loss of weight is relatively slow, so the attribute of the shocks that controls this is LSR. Lots of LSR makes the car feel responsive.

We could stop here and I would say that Koni yellows have the highest rebound-to-compression damping ratio of the OTS shocks for our cars, which is one of the reasons I argue for them. (Another reason is that they have shorter bodies than the other OTS shocks, so you can lower the car more.) But there's actually another issue.

As you increase the spring rates on a car, the springs themselves resist bumps more and more, which transfers more of the bumps to the frame (and occupants). At the same time, the amount of energy that can be stored in the springs is increased. So you need less and less HSC and more and more LSR as you install stiffer and stiffer springs.

Illuminas, for example, adjust both compression and rebound at the same time. So they don't work well with stiff springs because you are stuck making a choice: turn them down to get less HSC to have a better ride or turn them up to get more LSR to make the car handle better.

Koni yellows don't have this problem. The adjuster only changes rebound ... LSR in particular. So you can crank them up all the time and have good handling all the time. You can also - within reason - keep adding stiffness to the springs and turning up the shocks to get the needed extra LSR. The "wall" is up around 500 lbs/inch, which is higher than most people run on the street. (Those running higher rates are pretty serious about low-speed handling, so they are probably running real coil-overs with separate adjustments for compression and rebound, anyway.)

Getting back to your options: an AGX on full soft has more HSC than a Koni Yellow. If street ride is the key issue, you don't want them. Illuminas on full soft have less HSC than Koni yellows. So, again, if all that matters is the ride on the street, these are better than Koni yellows for low to moderate spring rates.

If you can handle a little extra roughness, then up the spring rates to the 500 range and get Koni yellows. Being able to crank up the LSR for autoXing is just too useful.

Note: my car has 500/450 springs and Koni yellows. I have a pregnant wife and 3yo daughter. Now that the car has a silencer on the exhaust, this is the car we drive as a family. Yeah, it ain't the same as the Legacy wagon, but it's fine. (As long as I remember never to lift in a corner.)

I hope that helps.

- Jtoby

 

[khendriksma1]

Well, that was a VERY informative post. I can see you have done your homework on suspension.

I think you have convinced me to buy the GC/Koni combo. I will probably end up changing the rear spring rate so that I have a 450F/350R setup rather than the 450F/250R that the set currently has. I guess the worst case scenario is that I don't like them and I end up selling them. It shouldn't be too hard to get most of the $375 that I will have paid for them.

I am only being this skeptical because I made the mistake of buying some of those cheap eBay coilovers a couple of years ago and only had them on for two days because the ride sucked so bad (with stock shocks). I realize now that was about the DUMBEST thing I could have done suspension-wise.

Thanks again for all your help.

Kevin

 

[jtmcinder]

450/350 is a fine place to start. Most of all, it's a safe way to start, because the car will have similar characteristics to what it has now, only better overall.

Do some autoXing next summer. (Or, if you're one of those lucky b'stards in a warmer climate, do some autoXing this "winter.") If, after a while, you find that the car still has too much terminal understeer, such that you have to trail-brake at corner entrance and wait forever before stomping on the gas at corner exit, then look around for some used 400s for the rear.

But be real careful about loaning your car to inexperienced drivers once the high-rate springs are on the rear. You lift in a corner and the tail is gone. End of story. My co-driver late this summer was coming from a Honda (understeer city). He spun on 40% of his runs in my car. But when he got the hang of it, he had an ear-to-ear grin.

- Jtoby

 

[khendriksma1]

Well, I really have no intention of auto-xing. Pretty much just street with a little drag strip.

Kevin

 

[my97mitsGSX]

so what would be the medium for street/drag racing as far as spring rates with the koni yellows.

450 front and 400 rear?

what spring rates do the GC come with originally. Where can I order different spring rates?

Thanks