[alpineweissm]

I have a 335is with M3 control arms front and back with Dinan camber plates and alignment pin out. Stock struts. Would going with a little stiffer front sway bar add any corning abilities on the track? Say the E93 M front sway? Also, i'm still getting more outer wear on my R888's than I care to see with -2.5 camber. Would a stiffer sway up front help even out my tire wear as well?

[Cloud9blue]

It will help a little, but don't expect a huge difference with stock springs, since sway bar is really just a multiplier for spring rate under lateral load.

[Kgolf31]

Originally Posted by alpineweissm

I have a 335is with M3 control arms front and back with Dinan camber plates and alignment pin out. Stock struts. Would going with a little stiffer front sway bar add any corning abilities on the track? Say the E93 M front sway? Also, i'm still getting more outer wear on my R888's than I care to see with -2.5 camber. Would a stiffer sway up front help even out my tire wear as well?

You'll never get rid of the outer wear

(Running -3.6* camber, going to -4* camber soon and will still have this issue)

[chris82]

Originally Posted by Kgolf31

You'll never get rid of the outer wear

(Running -3.6* camber, going to -4* camber soon and will still have this issue)

How do you still have outter tire wear with that camber? I know you have a fairly stiff/flat setup in front too...

[Kgolf31]

Originally Posted by chris82

How do you still have outter tire wear with that camber? I know you have a fairly stiff/flat setup in front too...

Cause 255 Tires on 9" wheel, running RE-71Rs and 26 PSI Hot.

Outside is left side


Outside is right side


This is after flipping, outside left side

[The HACK]

Originally Posted by chris82

How do you still have outter tire wear with that camber? I know you have a fairly stiff/flat setup in front too...

Because physics. No matter what setup you have the OUTSIDE half of the tire will always be doing more work than the inside half when cornering. Camber merely evens it out a little.

OP, I'm going to share with you two fairly well written articles, only because they agree mostly with MY point of view and frankly, I'm sick of typing the same stuff over and over.

http://oppositelock.kinja.com/why-yo...bar-1733925447

http://www.vikingspeedshop.com/the-t...out-sway-bars/

That second link is especially helpful, especially the cheat sheet near the bottom...Since the first half of the article really just rehash the basics.

And I will repeat this mantra once more.

Tires > Alignment Geometry > Springs > Dampers > Swaybars. Always try to solve your performance problems in this order. Actually, if I was to get back to my cynical self:

OS > Tires > BRAKES > Alignment > Springs > Dampers > Swaybars. Brakes has a far more significant effect on lap time and "handling" than just about anything you can throw at the car except for tires. But NOTHING fixes driving ills like some fine-tuning of the car's operating system.

[alpineweissm]

Originally Posted by The HACK

Tires > Alignment Geometry > Springs > Dampers > Swaybars. Always try to solve your performance problems in this order.

Excellent articles.

I'm on the stock sport suspension other than the control arms and camber plates, so it sounds like getting Koni FSD's next is probably going to have the biggest impact on handling. I gravitated toward the sway bar since it's much cheaper

I have two track days on my current set of tires. The wear doesn't look as even as Kgolf31's. I guess I have a lot of rotating to do in my future.

[natedog7700]

Definitely some good information on this thread, not to get off topic, but ive been debating swapping out my bald Pirelli run flats for Non run flats. Run flat sidewalls are extremely stiff so im not sure how i feel about the potential "sloppy" and less precise steering that comes along with non run flats. Do you guys have any input on this? Im looking at RE11A's to be specific.

[Ginger_Extract]

Glad to see my articles being mentioned.

Yes, a front bar will always help a McStrut car in terms of tire wear and grip. As long as you're not so stiff that you're picking up a wheel, it can only help. That said, in terms of balance, a front bar will add a touch of mid-corner understeer, but it helps the front end transition more quickly, so it's able to be driven around.

[Ginger_Extract]

[QUOTE=Kgolf31;19463878]Cause 255 Tires on 9" wheel, running RE-71Rs and 26 PSI Hot. /QUOTE]

More pressure. I know you like run them low, but it's a compromise. Running 225 on a 7" wheel on my H-Stock car, with -0.5* front camber, and wear is totally acceptable at 38psi hot.

[alpineweissm]

Originally Posted by Ginger_Extract

Glad to see my articles being mentioned.

Yes, a front bar will always help a McStrut car in terms of tire wear and grip. As long as you're not so stiff that you're picking up a wheel, it can only help. That said, in terms of balance, a front bar will add a touch of mid-corner understeer, but it helps the front end transition more quickly, so it's able to be driven around.

So the E93 M front sway is probably the best choice?

[Kgolf31]

[QUOTE=Ginger_Extract]

Originally Posted by Kgolf31

Cause 255 Tires on 9" wheel, running RE-71Rs and 26 PSI Hot. /QUOTE]

More pressure. I know you like run them low, but it's a compromise. Running 225 on a 7" wheel on my H-Stock car, with -0.5* front camber, and wear is totally acceptable at 38psi hot.

I don't care about the wear. 38 PSI isn't fast.

26 PSI is.

I'm competing for Nationals, I'll go through tires that's fine with me

[chris82]

Originally Posted by alpineweissm

Excellent articles.

I'm on the stock sport suspension other than the control arms and camber plates, so it sounds like getting Koni FSD's next is probably going to have the biggest impact on handling. I gravitated toward the sway bar since it's much cheaper

I have two track days on my current set of tires. The wear doesn't look as even as Kgolf31's. I guess I have a lot of rotating to do in my future.

Curious,how is the stock 335is suspension? Is it the same as the M-Sport E90 suspension?

[Cloud9blue]

Originally Posted by chris82

Curious,how is the stock 335is suspension? Is it the same as the M-Sport E90 suspension?

Exactly the same as standard ZSP suspension. There is no M-sport suspension for US market btw.

[alpineweissm]

[QUOTE=Kgolf31;19467480]

Originally Posted by Ginger_Extract

I'm competing for Nationals, I'll go through tires that's fine with me

How do the RE-71Rs compare to the R888s? I know the RE-71R has a 200 UTQG and the R888s 100. Should I switch, or are you bound to some sort of competitive restriction?

[Kgolf31]

[QUOTE=alpineweissm;19476887]

Originally Posted by Kgolf31

How do the RE-71Rs compare to the R888s? I know the RE-71R has a 200 UTQG and the R888s 100. Should I switch, or are you bound to some sort of competitive restriction?

I'm limited to 200 Treadwear Tires.

If I wasn't I'd be on Hoosier A7s

[The HACK]

Originally Posted by alpineweissm

So the E93 M front sway is probably the best choice?

From one of the articles I quoted:

As your static spring rate INCREASES, the sway bar thickness should INCREASE.

As your static spring rate DECREASES, the sway bar thickness should DECREASE.

As suspension travel distance INCREASES, the sway bar thickness should DECREASE.

As suspension travel distance DECREASES, the sway bar thickness should INCREASE.

As tire traction INCREASES, the sway bar thickness should DECREASE.

As tire traction DECREASES, the sway bar thickness should INCREASE.

If the car UNDERSTEERS, the FRONT sway thickness should usually DECREASE. (Not always)

If the car OVERSTEERS, the REAR sway thickness should usually DECREASE. (Not always)

While the above isn't always TRUE, it's a good starting point on determining if and when you'll need to ADJUST your swaybar stiffness.

Notice it doesn't say anything about using swaybars to FIX any handling or wear ills? That's because OTHER parameters makes a bigger return on investment in your suspension. If you're using stiffer swaybars up front to mask the lack of camber or poor wear due to spending too much time rolling over the sidewalls, you're throwing a bandage on a GSW.

To REALLY answer whether or not some swaybars up front will fix your tire wearing ills, you need the following tools. A tire thermometer. A video camera that captures the wheel's movement in relation to the chassis as you drive. And a photographer buddy who can take picture of your front end as you enter and exit a corner.

If you are seeing positive camber on the outside wheel in the middle of a turn as shot by your photographer buddy, what you'll need is stiffer springs (because the soft springs are allowing compression of the suspension well past the roll center). If you're not seeing positive camber on the outside wheel in the middle of a turn, but the inside wheel is seeing significant wheel movement on your video, then you need higher rebound control. If you're getting good camber gain on the outside wheel, little movement on the inside wheel, but continue to get really bad wear on the outside? Take a tire thermometer to the outside, middle, and inside of the tire to see if there's a drastic temperature change upon exiting a hot lap. If there is, adding stiffer anti-roll bar on a MacStrut CAN alleviate some of that lack of camber, because at this point you've likely already add 1) stiffer springs to combat outer wheel movement and 2) higher rebound to decrease suspension travel thus 3) higher swaybar rate up front will help.

But if you can't do either (stiffer springs or higher rebound rate), for whatever reason or compromise you need to make because NOT racecar, then to a certain extent a thicker front bar MAY help even out the wear. Or it may not, and actually exacerbate your handling woes because it increased the propensity to understeer, and if UNDERSTEER is what caused the uneven wear. That's the reason I rarely EVER encourage swaybar as the first fix for anyone serious about on-track performance, because it is the most dependent on other factors of the suspension and least predictable in its effect, especially on a MacStrut car.

As to your original statement, whether or not the E93 M3 swaybar is the best...The problem with using swaybar to fine-tune the suspension, is you need to FINE-TUNE it. So a static swaybar like the E93 M3 is designed to be used, as determined by BMW engineer, to work best with a chassis of E93 M3's weight, spring rate, suspension travel, and damper rate. IF you throw the E93 M3 swaybar on the car, and it works? Great. Perfect example of blind squirrels finding acorns. Ideally, you'd want a swaybar with some adjustability to it so you can figure out if it's too thick and causing you to run out of front grip mid corner, or still too soft given your changes in other parameters to fix your handling ills and thus allowing you to change its stiffness to a certain degree.

Buuuuuuut...As many here like to point out, and as myself have stated multiple times, I don't know Jack & stuff about cars and suspension. And Jack just left town. And frankly, you should NEVER believe what any internet poster has to say about anything, like I have stated multiple times, even if said poster has a well written blog with painstakingly documented laptimes and fact to back up his writting, that you happen to agree with (no offense Ginger_Extract).

So you should probably just disregard everything I just typed out, and go ahead and get that E93 M3 front swaybar.

[chris82]

Originally Posted by The HACK

From one of the articles I quoted:

Why should you increase the stiffness of your sway bar as you increase your spring rates? Not seeing any logical reason for this in the articles you mentioned. If you have a car that corners flat, why increase the sway bar stiffness? All it will do is lift up the inside wheel

EDIT: I know you that cheat sheet doesn't apply to all situations

[Cloud9blue]

Originally Posted by chris82

Why should you increase the stiffness of your sway bar as you increase your spring rates? Not seeing any logical reason for this in the articles you mentioned. If you have a car that corners flat, why add a sway bar? All it will do is lift up the inside wheel

EDIT: I know you that cheat sheet doesn't apply to all situations

Yeah, it is also weird it states why sway bar thickness should decrease when tire traction is increase. Wouldn't you want less lateral load transfer with thicker bar when you run stickier tires???

[gavronm]

Originally Posted by Cloud9blue

Yeah, it is also weird it states why sway bar thickness should decrease when tire traction is increase. Wouldn't you want less lateral load transfer with thicker bar when you run stickier tires???

Trying hard to remember my race car suspension engineering class almost 18 years ago now but I think I can answer this and the previous question.

The point to making these sway bar changes is to keep the lateral weight transfer "the same" (as a percentage of the total) as it was before the other change so you can isolate the effect of the other change on other handling parameters.

Assume for the sake of this mental exercise that your "perfect" setup has the inside tire with essentially zero vertical load but still just barely touching the pavement. Assume further that the non-sway-bar changes are NOT done for the sake of improved cornering (because you already have a "perfect" setup). The goal then is to keep the inside tire in the pavement-skimming "position" after making all the other changes.

For the previous question, when spring rates go up, to keep the lateral weight transfer the same you need to increase the sway bar stiffness. If you don't stiffen the sway bar the stiffer spring on the inside wheel will push that wheel "down" - if you will, and that tire will be carrying more load than it did before you swapped the springs.

For cloud9blue's question, stickier tires are going to allow for an increase in lateral g's, which will increase the available lateral load transfer. With the same swaybar, that increase lateral load transfer will compress the outside spring more and the sway bar will lift the inside tire up off the pavement instead of just barely skimming it. By softening the sway bar you allow that inside tire to drop back down to just barely skimming the pavement.

Before someone (ahem) jumps down my throat let me just say the whole skimming the pavement thing may or may not be ideal for a given car, I'm just using that as a reference point because it makes it easy to visualize effects of the changes.

Interesting result of this exercise is if you get stickier tires AND stiffer springs you just might be OK with that original sway bar.

[Cloud9blue]

Originally Posted by gavronm

For cloud9blue's question, stickier tires are going to allow for an increase in lateral g's, which will increase the available lateral load transfer. With the same swaybar, that increase lateral load transfer will compress the outside spring more and the sway bar will lift the inside tire up off the pavement instead of just barely skimming it. By softening the sway bar you allow that inside tire to drop back down to just barely skimming the pavement.

Interesting result of this exercise is if you get stickier tires AND stiffer springs you just might be OK with that original sway bar.

You have a point, but I still believe it is a bad idea to follow some sort of general rule of thumb when it comes to sway bars. The effects of sway bar is directly affected by other parts of the suspension, including alignment, suspension travel, camber gain/loss under compression, spring rates, and etc. What works for one car does not mean it will work for the other.

Let's take the stickier tires = softer sway for example. With a softer sway and grippier tires, you could end up so much compression on the outer side of the suspension, causing chassis roll and camber loss (as it would occur with the macpherson struts on the front end of our cars), you could significantly reduce the size of contact patch you used to have before and end up with less grip.

I think for non-aero cars like ours, the contact patch of the outer tires matter a lot more than that of inside tires, considering under fast corner, the inside tires are very lightly loaded no matter what kind of trick suspension you are running.

[gavronm]

Originally Posted by Cloud9blue

You have a point, but I still believe it is a bad idea to follow some sort of general rule of thumb when it comes to sway bars. The effects of sway bar is directly affected by other parts of the suspension, including alignment, suspension travel, camber gain/loss under compression, spring rates, and etc. What works for one car does not mean it will work for the other.

Totally agree. I was just trying to work through the theory behind the generalization. The problem with tuning a street car for the track is you don't know what compromises were made and in what order of priority to arrive at your starting point.