I am not sure what your profession is, but you seem to know alot more about suspensions than I. I will take your advice and try a set of springs to help reduce body roll. Do we know if the stock speings are progress or linear? progressive would explain the small amount of body roll present in the car.

I think tanabe's are the most streetable, however, I do want the wheelgaps to be even front to back...what does that leave me with...eibach? those are more than 5-10% stiffer right?

Knowing my goal of almost no roll and yet a smooth ride, would you suggest the eibachs?

 

Stock springs are linear. I'm not a big fan of progressive springs mostly because no one makes progressive dampers so you're always going to be compromising the damping settings with progressive springs.

AFA brand recommendations, it's a tough call. Most aftermarket springs are intended to lower the car first, and typically don't increase the spring rate enough to counter increased roll couple from the drop which is why aftermarket sways are so popular. Without doing the homework on the suspension (figuring out the roll center and what happens to it at different ride heights) it's impossible to give a decent recommendation. Short of doing all the homework, you'd be best off finding a CL member with springs installed and taking a ride in the car to see if you like it.

 

If understeer is an issue for you, another thing to consider with springs is to try transfer a little stiffness to the rears. Put another way, let's say the stock springs are 300 and 300 lb/in front to rear. By going with 350 and 400 lb/in in the aftermarket springs, you will tend to reduce the understeer of the car.

Don't mean to muddy up the water any further but some don't take this into consideration and unknowingly increase the understeer built in at the factory.

 

^everything but sways

 

Whats all this negativity towards aftermarket sways in the IS crowd? It seems as if most of us guys in the GS section have upgraded sway bars. I know for sure that my car handles better with these than it did previously with the stock pieces. I have a G-meter readings as proof, and also beating a certain German car with an M badge through corners as some evidence

On a second note, I do have Tein Flex coilovers so the sways are much better matched VS someone putting upgraded sways on a stock suspension.

 

It's not negativity. It's intelligent tuning. Start with springs. Match sways to springs if necessary. Comparing your GS to our IS is apples and oranges. Completely different starting point.

 

It seems to me like springs and sways should be upgraded together (matched), since intuitively, stiffer springs would reduce the effectiveness of the stock sways. I realize that intuition is often wrong...

 

It's a maybe. It all depends on the compromises the engineers made at the factory. Did they opt for softer springs and a more compliant ride while making up for the lack of stiffness with stiffer sways (the sways on the car are not small) or did they match them dead on, or...the only way to find out is to try the changes and see how they work together.

Still, no one is making sways yet, so there's some empirical data that the OEM sways are pretty beefy.

 

I don't see how it could be a maybe. Well, I guess I could see how lowering the roll center might make it a maybe ...

The whole point of tuning anything about the car is to alter the compromises that the OEM made. It is my belief that they chose an undersized rear sway bar to increase understeer. I would do the same thing in their shoes, but I prefer a more neutral balance for myself. If someone offered an adjustable rear, I would leave my front bar alone.

My reason is because I hate the amount of understeer this car has with OEM tire sizes. On top of that, I want a wider / lower profile rear tire so that I can improve gearing a bit and still be able to go full throttle without totally losing traction. If I do that, my understeer problem will get even worse.

 

Tuning suspension is like tuning a Honda engine. Change one thing, 20 other things need to be adjusted to compensate for the change. So it's all a maybe...

The last feature that makes me wonder about changing the sways is knowing the sport suspension package uses the same sways as the lux package. So I suspect they've erred on the stiff side.

If you want more rear sway, have you looked at drilling a second hole a bit forward of the original one? This is the quickest and easiest thing to change the rear sway stiffness.

 

Well, that's why I figured Eibach would do the homework for us, and design a matched set of sways for their springs. I would hope that they would do enough R&D to know what 20 other things happen when their springs are installed.

Regarding the sport package, it only lowers the front by .5", and doesn't change anything else, right? In that case, I wouldn't expect that much of a change in sway bar requirement. Didn't they actually make that height adjustment in a way that might not have even changed the roll center?

I haven't considered changing the "lever length" of the stock sways. If there is room for new bolt holes, then I would consider lengthening the front arms and shortening the rears. However, it seems that there needs to be a very significant change to accomplish what I want. I've already set my front and rear toe out to the most agressive end of spec, and it didn't seem to help much.

BTW, I don't see the analogy about Honda engines, since tuning my S2000 seemed so easy...

 

I've tuned a lot of Honda bike engines. Change compression, even a small amount, and you have to change 20 other things to compensate and get the increase you expected in the first place. Same thing with cams, fuel system, lightening rotating parts, etc., etc., but I digress.

The front is dropped 10mm, not even 0.5". It invariably lowers the roll center, there is no escaping this unless they compromised the roll center at standard ride height. It's basic geometry, there's just no way out.

What we don't know is the spring rate on the sport springs. It has to be higher, and the sway requirement is based on preload and spring rate. Generally a higher spring rate needs a stiffer bar for the same effect, except that the stiffer spring inherently provides more roll resistance, so it may not be necessary to add roll stiffness using the sway bar. That's the trade off.

That's why I said, start with springs. You add roll resistance with stiffer springs. Drive the car. See if it meets your expectations with just a spring rate change. If it doesn't, and you are happy with the ride on the stiffer springs, THEN change the sway for even more roll resistance. Don't forget, the whole reason the suspension guys put sway (roll) bars on the car is because it allows them to run softer springs for better wheel compliance. If it weren't for that, we could ditch sway bars entirely and keep our fully independent suspension design.

 

If you want to get rid of the body roll, you would have to lower your car. I think sway bar is controlling under or over steering.

 

Lowering makes roll worse, not better. See discussion about roll couple for more information.

 

I thought the sport suspension just had different knuckles, or something. If so, it wouldn't necessarily change roll center any more than putting smaller wheels / tires on the front.