Okay,

Here's what you need to know, i have an 06 base, and i was in the market for coilovers about a year ago. I was originally looking at Bilstein, KW V3, or used Zeals based on the ease of use ("no true coilover set up bushing fatigue problems", and complimets paid by board members referring to ride quality). I did my homework, so I started researching spring rates. This is what i found

Stock 03-04.5

Front 6.1 kg/mm
Rear 6.4 kg/mm

(Too much push) Nissan corrected the problem!

04.5-current

Front 5.6 kg/mm
Rear 7.6 kg/mm

I felt the balance was perfect, just a tad bit of push but can be solved with about 1/2 to 3/4, only problems for me were overall softness and ride height was too high.

So Why is it that most all of the aftermarket coilover companies offer kits with spring rates:

F 12kg
R 10kg

or

F 10kg
R 8kg

Is it just me or does that seem like a bad idea? It doesn't take a rocket scientist to figure that the car is going to push quite drastically, that's a 4 kg/mm difference in overall ratio front to rear!!! i say this because i race Formula cars professionally and in all my experiences, once you find a good handling balance, you keep the spring difference (ratio f to r) the same, and move up and down the spectrum while tuning shocks and alignment to cure problems from here to there. I know rake is effective and can be dialed in to help rotation issues, but then you look like a 1/4 queen.

I knew i wasn't going to abuse my Z on track, but i do love the dampning and ride height adjustablility that comes with coilovers, so i wanted a set that wasn't too stiff and retained at least something close to my stock balance. With all that in mind, i purchased a set of HKS Rs coilovers with rates of

F 8kg
R 8kg

Basically what i felt was the least of the big mistakes. Does anyone else share the same concern as i do? I know my car understeers fairly bad now, alot more than it did stock. I'm thinking of trying to get either HKS to make some 10kg rears, or possibly talking to swift to get some. Does swift sell the diameter that the HKS Rs uses?

If that fails, i'm going to get adjustable sway bars and try and dial out some of the push with a stiffer rear set-up then up front. But i'd really like to cure this the right way with springs rather than bandaging a problem with a sway bar.

Anybody with some insight custom spring info and sizing would be greatly appreciated! Or anybody with a shared concern, feel free!

 

Under hard braking your car is going to have alot more weight in the front, hence a higher spring rate in front will keep the car more balance once u let off the brakes and transitioning into a turn. Again there's alot of other factors that will cause understeer, espcially after installing a set of coilovers. Your allignment, front and rear camber will be off after install coilovers and adjust your ride height. Once allignment is done, you'll feel alot different. And also corner weighing the car will probably bring that balance that you are looking for.

 

First and foremost, you are overthinking things a bit, because as soon as you change tires and align the car properly, you can toss the stock Z characteristics completely out the window. Second, as you alter spring rates, valving should change too. Given that this changes the interaction of the damper and spring, it also will change the cars characteristics. Alignment plays a critical factor in over/understeer. So do swaybars. My point is nothing operates in a vacuum - so don't look at it as a zero sum game, it's not. A Z is nose heavy, and as such, front rates should ideally be stiffer. It might sound counterintuitive to what you are used to be its proven itself to work time and time again, year after year.

HKS don't offer custom valving services, so if you uprate the springs you'll have to find someone who can revalve them. I own the same coilovers, I've never felt the need to alter the valving or rates in any way. My car is just as fast around the tracks I run on than my ITS BMW is.

If you study the threads, you'll see the same recommend units coming up again and again by guys who know what we're talking about, such as us, G35sedan, and a few others. Study these threads, and you'll end up with something suitable for your needs and budget

 

all you need is a stiff rear sway bar and leave the front sway bar alone to regain your balance. Of course it depends on your tire sizes too (front vs rear)

also things like what LSD and power you run can give you the ability to oversteer at will anyway

+1 to the fronts need to be stiffer when braking from high speed. Even with 10kg springs up front, I wish my car wouldn't dive as much as it does when doing hard braking even from just 80mph. It's not too bad though

 

i know about the valving, but it just seemed odd to me considering the spring being the starting point of the suspension, but the more and more i read about bars, i think that's going to be the most practical way to go! As well as a good corner weight, i'm hoping the rear will be happily singing behind the front end. No more of this plow! thanks for the interest guys!


As a side note, does anyone know how long HKs takes to rebuild a shock? I'm pretty sure my right front compression valve needs a once over. The rebound adjustment is still useable and noticeable when adjusted, but it's the initial shock imapct on a sharp bump that seems a bit soft and oscilates alot more than the left front or the whole car for that matter. It seems to pivot over bumps on that right front corner, the only thing i can think is that eventhough the coilovers are the same height from side to side, the right front is a bit lower assuming more of the load, but i don't think if it's not visable that'd it be dramatic enough to make the difference i see and feel.

 

OP: You mean more oversteer with a stiffer suspension in the rear right?

 

yes, i mean more oversteer in the rear. A general rule of thumb to use is: whatever end of the car (front or rear) is stiffer in realtion to the weight proportion of the vehicle will slide first. Assuming you had a perfectly balanced car, stiffening the front will generate a push, and stiffening the rear will induce more of an oversteer attitude to the handling characterisitcs.

a good example is a mustang, is has a 4.6 litre iron block that is very very nose heavy. Generally speaking, the car's front end will loose grip before the rear will (assuming you dont stab the throttle).

 

Also, you can't compare rates of stock spring locations to coilover spring locations, they have different leverage.

Chris

 

study!!