[Bootsie]

I know some related posts have been made, but I keep getting confused on how to do them. I am currently quite happy with my suspension performance with Prodrive springs (stock struts) and 27 f/ 22r sways. The only problem is they still have more roll than I would like.

Can someone tell me....

If I increased my sway settings to 29f/ 24r, how much softer would the spring rates need to be to keep the effective spring rate approximately the same? (I realize the Prodrives are progressive, so even an approximation would be appreciated.)

Would I have to go even softer if I wanted the car to flex the outside suspension as much as it did before. (Since there would be more resistance from the inside struts- due to the stiffer sways. whole car would be lowered- instead of just the outside. )

Thanks, and any help would be appreciated.

J

[Bootsie]

Just in case anyone wanted to know, I found a graph on Whiteline's website that charts how much the spring rate goes up when you up the sway bars. The change from 27 to 29 was 33% and the change from 22 to 24 was 42%. (EDIT- BTW, according to the chart, the increase stiffness from stock (20mm) to 29mm is 342%. I am guessing this does not adjust for the diameter variation of the 29 bar, though.)

QUESTION- To maintain my current overall spring rate, would I have to adjust my springs down 33%, would I need to halve that (to 16.5%, due to having two springs connected the the sway), or is there is something else I am not taking into account? (I suppose I could get a higher damping rate, but I would then want to lower the car a fair amount to get lower in the turn.....)


Also, going off Stretch's (admittedly rough) estimate (he mentioned it did not account for the change in diameter of the Whiteline bar), this would bring the front rate from 1877lb/in to 2477lb/ in. (This is with an adjustment for the wheel rate.) Even though it is a high estimate, those are some high numbers!

Any advice would be appreciated.

J

[waktasz]

The sways only affect roll stiffness, when cruising down the highway, the swaybar does not affect your spring rate at all.

The sways also don't change your spring rate by that much when turning. I'm not sure how much, but definitely not 33% of your total spring rate.

And those rates are way off...1800lb/in ?!? Where did you get that number from?

[twiSTies]

I'm a bit confused on how you want to cut down on roll, but want to keep the spring rate the same. You can adjust the swaybars stiffer for more roll stiffness, which would do what you'd want, but by then lowering your spring rate, you'd only be back where you started.

[4banger]

Originally Posted by Bootsie

QUESTION- To maintain my current overall spring rate, would I have to adjust my springs down 33%, would I need to halve that (to 16.5%, due to having two springs connected the the sway), or is there is something else I am not taking into account? (I suppose I could get a higher damping rate, but I would then want to lower the car a fair amount to get lower in the turn.....)

When you think about this, you want to think of each corner of the car as a spring/mass/damper system.

1. You need to calculate the ammount of mass being supported by each strut based on the weight distribution of the car.
2. Calculate the wheel rate for the front of the suspenion based on the spring constant of your front springs.
3. Calculate the spring rate of the sway bar and then add that to the wheel rate using the motion ratio for the sway bar.

When you corner, your car will roll as weight is transfered off of the outside front wheel. The most weight that can be transfered off is the same number that you calculated for that corner in 1. You can then determine how much that corner of the suspension will uncompress based on the wheel rate of that corner (inches of uncompression = mass of corner / wheel rate of that corner).

So, if you want an estimation of what spring rate you would need to have for the same ammount of roll if you stiffened the sway bar, use your estimate of the new sway bar rate and recalculate the wheel rate. Then solve for inches of uncompression using the known mass of the corner and your new wheel rate.

I'm not sure what you are talking about with regards to lowering the car to get lower in the turn. Your goal should be to have as little roll as possible to stay in the 'good' part of the camber curve. Lowering the car on stock struts takes you out of the 'good' part of the camber curve. if you descide to get new springs, you should try and pick ones that maintain the stock ride height.

[4banger]

Originally Posted by waktasz

The sways only affect roll stiffness, when cruising down the highway, the swaybar does not affect your spring rate at all.

The sways also don't change your spring rate by that much when turning. I'm not sure how much, but definitely not 33% of your total spring rate.

And those rates are way off...1800lb/in ?!? Where did you get that number from?

I think you should read this thread Sway bars and total spring rates (why sway bars sometimes do too much).

[CGMDan]

And if your not racing, looking for that last .01sec, does any of it really matter?

[stretch]

Here ya go, just plop in your spring rates:
http://www.fromsteve.net/carstuff/su...ensionCalc.zip

(I've been working on this a while and will start a new thread for it once I'm sure it's correct.)

[Bootsie]

Thanks for the responses, guys. I am out of town and having problems with this computer, so I will look at this closer when I get back home next week. (I cannot seem to open Stretch's link on this computer, but I really want to!)

J