I'm looking at a set of used eibach multipro coilovers. The springs on it are 550lbs fron and 450lbs rear. According to AM the stock eibach springs should be 225lb front, 250lb rear.

Wouldn't 550/450 be extremely hardcore track stiffness?

 

Those are going to be pretty stiff and harsh on the street. Not sure if that is something you can live with

 

yeah but what are you trying to achieve? better make sure your fillings are all secure, as you will be rattling your teeth on the street.

 

What rates would be ideal for occasional track use, comfort on the road but still maintains impeccable handling?

 

here's my thoughts but i'm not an expert. while dealing with Ground Control and Eibach to redo my suspension, i was after basically the same thing you are. the rear spring rate affects ride quality a bit more than the front so keep that in mind. stock spring rates on our s197 was around 136 and 142. my ground control system replaced them with eibach at 225 and 200. stiffer fronts i believe that gives a bit better handling. I don't autocross my convertible though and verts weight distribution is a bit different than coupes too.

I worked with hypermotive and eibach directly so i would reach out to them and ask

 

That depends on if you have adjustable dampers. If you have fixed valved dampers you probably want a bit higher spring rate. BMR makes their race springs at 240# for the front for example.

I have Steeda Sports which are 200# front and 175# rear. I find this the perfect spring rate with Koni Yellows which are adjustable. I go 3/4 stiff front and 1/2 stiff rear, and it makes the car feel really flat, hard and hooked up on the track. Too stiff for the street. Bu for the street I use the full soft shock setting.

 

I've been wondering about this, while we're on the topic:

The Koni yellows are adjustable for rebound damping only, correct? Which means that when the springs have been compressed, they wil rebound more slowly / take longer to return to "rest" position with the "stiff" setting. The rebound damping makes no difference on compression.

So how does that make the car ride flatter?

Small tangent: I have the steeda sport springs also. I am thinking my next related upgrade will be Bilstein shocks/struts, which are a high pressure gas shock. If I understand correctly, this means they have their own additional spring rate which effectively increases the total spring rate on compression. I'm thinking that would be even better . . . ?????

 

You are correct, rebound only is what Koni Yellows allow you to adjust.

So how does that help with flatter cornering? Here is my best explanation:

When the car enters a corner 2 things happen. The outside compresses, and the inside rebounds. By slowing down the rebound, the side that compresses has to slow down also. So the force that causes the lift of the inside is counteracted. Therefore the car stays flatter through curves.

I've heard a similar arguments about the mono-tube shock design. I'm not sure here to be honest. One side fits all argumentation is what makes me nervous about that. But again, you are right, there is more of spring rate effect with mono tube. I haven't had a chance to compare dual chamber and monotube design effects back to back yet. I'd love to though.

 

That makes sense; I thought of that too when I was thinking about this more after posting. The rebound damping keeps the inboard side from going up. Same thing during braking, keeps the rear end from going up. I can see how this would help especially for S-curves where you get that side to side rocking motion.

 

Yup, I'm thinking the same thing. Having adjustable compression would also be a big plus though.