So quick question guys. So i've been driving around with a ST front and stock rear sway bars and definetly notice better handling but I've noticed i've been getting a little too much understeer from it.

I have it on the tighter setting and am not sure whether or not the "looser" setting will offer that much of a difference.
So im looking to see if i should get a thicker rear sway bar to counter act the understeer.

First off my question is: The difference in thickness between the front and rear sway bars are what causes the understeer and oversteer charactersitics respectively right? So if i get two thicker bars but the overal ratio of thickness for the thicker bars is the same as the stock ratio...would it make any difference in handling?

DATA:
Stock s4 base sways:
.866 in
.472
difference: .394 inches

ST front and stock rear:
1.125
.472
difference: .653 inches

ST front and ST rear:
1.125
.75
difference: .372

ST front and RB rear(ST front is same as RB front other than the adj.):
1.125
.625
difference: .5 inches


So would the ST front and rear sways actually cause more oversteer charactersitics than the stock setup?

Are there other factors? And does this ratio affect anything?

 

It depends a bit on your other suspension components/tires. Typically you can increase the rear's to produce oversteer. If you went Stock Front/ST rear it should give you a bit of a tail happy experience. I used to run an RB front with if I recall an ST rear which gave me a pretty balanced setup.

 

good topic, we need more info! I've two have been thinking about the difference between bars available and it's effects with stock shocks and springs

 

yea im not looking for a tail happy experience lol but i am looking for something balanced instead of understeer. The rest of my suspension is all stock.

 

I'm interested in this thread. I just got a cheap strut bar in the front, seems to stiffen it up alot, not sure if i notice understeer but the fc understeers, then again I was going very very high speeds. I don't want the rear to go out more, its fine (Need to get DTSS eliminators though) not sure if I need wider front tires or something else

not tryin to thread jack ya

 

to the OP, what kind of setup are you going for? what suspension do you have?

 

With stock components you're generally going to be rolling the weight into the outter tires on cornering, the rear being stock swaybar is going to roll over the most and tend to stay in line, the fronts aren't going to want to roll over so you're going to instead put the cornering on your springs/tires, which often leads to understeer. When you put them on the back as well, you sort of balance it back out again giving it a more neutral feel. But this depends on your other suspension as well, as obviously theres different thickness/balance etc. Hard to explain at 4:30AM.

 

your experiencing understeer because you just stiffened up the front end only. Your rear end is softer thus having more grip out of the two.

And their sway bars where designed to be teamed up as a pair installed on the car.

 

yeah, what I experenced seemed like the front end was too light, if i gave much throttle at all on corners (going through slight turns pretty fast) I noticed the front end felt like it was on water alot yet it was dry road, kinda alarming at whatever speeds I was going, i think 60 ish which was probably pushing it alot lol

 

Yeah, the problem gets shifted to your other components then, that's why I typically like to do the majority of the suspension work at once.

 

No, it doesn't work like that. A sway bar's stiffness, assuming all else is the same (bar length, arm length, attachment points and so on), which is a pretty safe assumption for a stock replacement sway bar, then the stiffness is directly propotional to the 4th power of the diameter. So to compare, take the 4th power of the diameter of the various bars (d^4) and compare that.

With the suspension arrangement of the car, as you stiffen the front, you keep the car from rolling as much, which helps keep you from losing negative camber, which helps maintain grip. The rear doesn't do that, it has decent camber gain, which will at least partly cause the handling balance to change even if you stiffen everything up to the same ratios as stock.

If I were you, I'd just get the ST rear bar and be done with it. IIRC the d^4 ratio indicates a slight increase in oversteer / decrease in understeer compared to stock.

 

Black91N/A is correct about the math but you are thinking about it correctly.


Start with a larger rear only and see where you are at. A larger rear will increase oversteer. You could then put on a larger front, and increase understeer. Depending on the size of the front bar, the oversteer condition could be better or worse than what you started with.

 

as of now my suspension is completely stock minus the ST front bar and a mazdatrix three point strut bar

Im planning on selling that three point and going to a generic two and getting koni inserts all around with stock springs because im trying to stay in my autox group STS.


Black91n/a

thanks a lot for the informative post. I should probably read up on mor suspension books or what not but whats the background between the diameter to the 4th power? if its too much to explain dont worry about it but thanks again.

 

The 4th power comes from the formulas to calculate torsional stress in a round bar, where you use the moment of inertia of the bar, which uses the 4th power of the radius (if you're just comparing them, you can do it with the diameter, the ratios work out the same).

http://en.wikipedia.org/wiki/Torsion_(mechanics)

 

Has anyone ever use both the RB front and rear?

 

Sure, lots of people. I have them front and rear on my car.

 

man suspension stuff is so confusing. so many components to make a balanced car. Any books out there that i can read up on about it? that arent toooooooo engineer-styled lingo? lol

 

well dude just read the forums its free,.. take the time to see what everyone else is running.. typically you would want to upgrade your shocks/struts first, than i see sway bars after that. But also consider that others have different opinions/preferences on their setups.. Some guys like coilovers, some guys like shocks/spring combos, some guys like no rear sway bar setups. etc. It goes pretty deep with the FC since it has a pretty unique suspension design in the rear, typical ideal setup for other cars may not work so well with the fc.

 

90% of the info on forums is wrong.


Spend $20 and read a good book on the subject.

http://www.amazon.com/Tune-Win-Carro...d_bxgy_b_img_b

 

well with anything you read on the net, take it with a grain of salt, but still gives you an idea where to start.

 

yea thats the book i was looking at. I'll take a good look through it.

 

the thing is FC is a lil funky on the suspension, the general ideas may not be the best on it due to its suspension design

 

There is nothing funky about it. The front is a McPherson strut design - about at generic as you can get. The rear is a glorified trailing arm setup with reactive toe.

All the normal stuff pretty much applies.

You don't have to get all the math the first time through a book like Tune to Win, just try to pick up on the basic principles and go from there.

 

True,
You just need to learn the feel of your car, and take into consideration all the elements to having a great suspension work for you. I enjoy running the KYB's with no strut. The FC's handling is immaculate so anything would greatly enhance the ride.

 

That is the set up I use on my 10thAE as well. Stock heavy duty bar in the front, ST bar in the rear.

Adds just a slight bit of oversteer, so that the whole car is a little more balanced and predicable on mountain and sweeping style roads.