Suspension question

[PhoebusApollo]

I realize that to have ideal geometry in the car there's a lot of math do be done to calculate the stiffness of the parts in my suspension. I'm looking at purchasing a set of TEIN coilovers (likely the SS) and the springs are interchangable. If I were to purchase the Tanabe Anti Sway bars (30 and 27mm) what would the best spring be for the TEIN's? I know there is a ratio there, but math is not my strong point.

[aither]

I don't know about an ideal geometry being so important, except in terms of roll centers. I think most of what is important is driver preference/style. With the larger anti-roll bars, you have the option of running a less stiff spring, performance wise. Also spring rates should be matched with the coilover's dampening. Getting too stiff or soft of rates can be a bad idea in terms of shock life and performance. It might help if you mention what you are trying to achieve with the car, and what you want from it. Do you want more oversteer, less, etc?

[PhoebusApollo]

Believe it or not (and I am taking great risk in saying this on this forum... ) I don't want the car to drift. I'm interested in as much "bite" as possible from my tires. Where I live there are a plethora of very twisty roads, and the highest level of traction is my goal. However, if the tires do break loose in the rear, I would also like that to be predictable and controlable. Is that too much to ask? :-D

[Q45tech]

Tires breaking loose is a tire problem! Not a suspension problem as changing the relative forces on the tires has to do mostly with body weight.

Changing the rear stiffness by increasing the rear sway bar removes traction from the rear.........makes the tires wash out sooner. The rear already as much more traction than the front [why we say the front understeers] without acceleration.

The usual problem is tire compounds which are way to hard [to increase longevity].

Increasing the front tire load rating [strength] is a good way to help increase the front predictability. Front always washes out first due to excessive front weight.

Obviously as you accelerate a RWD car the rear tires must share: the traction gets divided amongst handling and acceleration.

You surely don't want to stiffen the rear much beyond 10-20% [from oem stock springs and rear bars] if aggressive wet weather driving is a consideration.

Having progressive rear springs is less ideal in wet weather as, if you lose it, recovery is much harder as the rear swings out becuase most match the shocks to the softest part of the progressive spring rate not the stiffness part.

Sometimes you actually use a softer front sway bar with the addition of a MILD rear sway bar.............all about the solution to the math problem..........different ways to skin the cat.

[PhoebusApollo]

Ok, so let me see if I understand this correctly. The smaller the diameter of the bars, the less force they are exerting on the tires. As I picture it in my mind, the tortional force they exert reverses any camber on the wheel, bringing the bottom lip of the wheel in towards the center of the car, reducing contact patch and causing the tires to slip sooner? Therefore the less amount of force the bar exerts the more cambered a wheel will be, increasing (to a point) the amount of contact patch in a turn and increasing grip? And the suspension allows for travel in a wheel in an up/down motion only, keeping the tire on the ground as much as possible? So if I want maximum grip and a soft ride, I would want a soft anti sway bar, and a high/normal ride height with a small amount of rebound. Do I have it? Or am I retarded?

[whiterps13]

i think before you even look at the suspension you should highly consider r-compund tires. these will give you more "bite" than most suspension upgrades, but to utilize the grip fully you will want coilovers, sway bars, and struts bars. these may also provide so much grip that some weaker parts in your suspension (ie. bushing, tie-rods, tc rods etc...) should be upgraded too. as far as your original question i think you have understood it pretty well.

[Nismo_Freak]

Ok, so let me see if I understand this correctly. The smaller the diameter of the bars, the less force they are exerting on the tires. As I picture it in my mind, the tortional force they exert reverses any camber on the wheel, bringing the bottom lip of the wheel in towards the center of the car, reducing contact patch and causing the tires to slip sooner? Therefore the less amount of force the bar exerts the more cambered a wheel will be, increasing (to a point) the amount of contact patch in a turn and increasing grip? And the suspension allows for travel in a wheel in an up/down motion only, keeping the tire on the ground as much as possible? So if I want maximum grip and a soft ride, I would want a soft anti sway bar, and a high/normal ride height with a small amount of rebound. Do I have it? Or am I retarded?

A soft rebound along with a high amount of travel length would lend towards a "softer" suspension feel as Dennis (Q45tech) has outlined before.

What I would suggest to you would be to get a moderate stroke, using a soft compression in the rear (to allow throttle input to take effect quickly, and change weight faster), and keep the rebound settings hard to allow you to re-transfer any resulting oversteer from the weight shift. Use a high spring rate (like 7.0 kgf/mm - 8 kgf/mm) in the rear with a 250mm spring.

As for the front a solid 10 kgf/mm 200mm spring or 225mm spring along with slightly harder compression, and a moderate rebound would work well.

For the roll bars... I'd stick with a small diameter, this is my personal preference. The spring rate should accomodate most of the travel and roll resistance. If the car suffers from excessive roll, then more than likely the car is lowered too much causing the roll center to be out of spec. Reworked lower control arms can fix that to some extent, but for the most part 240s do not like to be slammed.

Tires are by far the best investment you can do towards a car's handling. No matter the amount of weight tuning you do, or modding the suspension geometry, you're still limited by the amount of grip the tire can give.

TiresSuspensionCornerweightAlignmentRoad Testing (heat, pressure, etc.)Recalibration of Alignment

BTW, AFAIK the sway bar only effects the roll resistance of the car by tie-ing in the lower arms with a rigid bar. It effectively adds progressive spring rate via tension. Therefor the only effect it has on camber is the reduced amount of suspension bump. So from there, based on your static camber you can deduce if it is reducing your contact patch. If thats the case you need to remove static negative camber from the rear or deminish the amount of bump.

[Q45tech]

I disagree, as body roll is good, it warns you in wet weather long before breakaway occurs.

Taking an oem rear designed 3.5" [half of shock stroke] and reducing it by 2/3 to +- 1.0 " with 7kg/mm [391 pounds per inch] springs [or spring sway bar combos] is pretty radical for the street [where you find bumps as opposed to racetrack where you don't].

"if the tires do break loose in the rear, I would also like that to be predictable and controlable. Is that too much to ask? :-D"

The above is what the factory builds in, safe controllable recovery for novice drivers who don't understand the physics of driving!

Thats why you don't change things very much back to my 10-20% not 350%.

Obviously there are those that want bone jarring non compliant chassis and the oem feel and minute steps inbetween.

[Nismo_Freak]

Thats why you don't change things very much back to my 10-20% not 350%.

Obviously there are those that want bone jarring non compliant chassis

[PhoebusApollo]

Ok then... By jove I think I've got it... thanks all!

Oh btw... I do have to get a suspension. My struts are blown and I have an inspection soon and Nissan wants something like $300 per corner, so I figure why not spend that money on something nice.