Can someone explain why the roll stiffness of the anti-roll bar is dependent on the coil spring rate? Maybe I'm missing something...

Though the springs and anti-roll bars are coupled systems, their roll stiffnesses are characteristics of themselves....not of the system as a whole. Together they define the roll stiffness of the chassis. I can definitely see the amount of force that each system applies is impacted by the stiffness of each system. For example, if the coil springs are swapped for stiffer units, the anti-roll bars will not apply as much force because the chassis will not be rolling as much. Similarly, if the anti-roll bars are swapped for stiffer units, the springs will not be applying as much force during body roll.

I think the above statement should read, "The reaction forces contributed by the bar is dependent on the springs..." Agree, disagree?

 

No camber joints, no front aero. Why do you sy that?

I'm inclined to agree with you, I think total roll stiffness is total roll stiffness (in an ideal, steady state, completely flat track, etc) no matter where it comes from. But don't listen to me, I turned a fast car into a slow car last time I messed with this stuff


Ok, so here's the calculations I came up with. Assuming my car was properly balanced before I started changing bars and springs and I then replace the replace the Saner (on the middle setting) with a stock '01 bar, I get a bar difference of about:

667 lbf/in - 300 lbf/in = 367 lbf/in

Converting that to a difference in wheel rate:
wheel rate = sway bar rate * motion ratio ^ 2
wheel rate = 367 * 0.53 ^ 2
wheel rate = 103

Convert that wheel rate back into a spring rate:
spring rate = wheel rate / motion ratio ^ 2
spring rate = 103 / 0.7 ^ 2
spring rate = 210

So I put on 100 lbf/in extra spring, but really I needed 200? Am I doing this right? Or did I simplify the equation too much?

 

I calculated all of this awhile back and I think the thread can shed some light on just what you are asking.

Sway Bar Motion Ratios and Calculated Spring Rate/Roll Resistance

I also have a spreadsheet I put together that generates all this stuff. It allows me to juggle sway bars and springs by theory. I used it to successfully add a big front bar and the stock rear bar and maintain similar handling characteristics.

 

[QUOTE=FormulaRedline,Oct 15 2010, 07:56 AM] No camber joints, no front aero.

 

I just installed my J's S1.

Camber range is approximately -1.6 to -3.8. My precursory alignment has the camber adjusters at half, yielding -2.4.

Toe varies WILDLY with camber adjustment from 3/4" to -1/2". The car toes in when adding negative camber.

Stock balljoints:
camber: -1.8 (adjusters maxed)
toe: -1/16"

J's S1 balljoints:
camber: -2.4 (adjusters middle)
toe: 1/8"

You cannot just install these joints then drive on the street. A rough alignment is necessary to get to an alignment shop. Install the balljoints then adjust the camber from max to roughly half. Toe should be +/- 1/4" if you started with numbers similar to my car.

 

I found when installing these on my car, that if you hold the outer tie rod and turn the inner tie rod 10 flats that that gets you back to where it was to begin with.

FWIW: I started with -2 and now at -3.5

 

[QUOTE=chetly,Oct 18 2010, 04:24 PM] FWIW:

 

running 650lbs springs square, saner front bar on 2nd hole and no rear bar, the outside tire temps were about 20 degree's hotter than the inside, therefore the need for more negative camber.

 

That makes a lot more sense, thank you.

My rough math puts my roll rate approximately 50% stiffer than yours. It only makes sense my car would need less static camber.

 

Surprised no one has commented on this yet:

STREET TOURING
- In light of further member input received since its prior meeting, and per the unanimous recommendation of the STAC, the
SEB has reconsidered its earlier decision and is recommending the following change to the BOD, effective 1/1/2011:
- Delete 14.2.F

no lips, wings ect. I think its going a bit far and am now wondering if my OEM trunk lip is going to have to come off for the national tours