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      10-29-2012, 05:55 PM   #23
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To the OP - it's really dependent on what you feel the car is doing. What works for me and my driving style might not work for you and yours. The sway bar and minimize body roll on turn in - but so can your driving style by turning in earlier and slower. It's all about setting your car up for you.

As people said earlier - yes a sway bar can solve some understeer issues. Usually the issues that it solves are issues caused by body roll and the tire rolling over onto its outside edges.

In a properly set up car (camber plates, suspension, etc), this may not hold true - where adding a front sway would most likely cause more understeer.
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      10-29-2012, 06:14 PM   #24
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If you are on stock or near-stock spring rates, a bigger front sway bar on its own can make the car behave better in pretty much every way. This was my experience on my car with stock springs and RDSport front bar. Better off-throttle behavior, more settled in transitions, better corner exit traction. It's a good way to gain roll stiffness if you want to or are required to stay with near-stock spring rates, with no real downsides other than dealing with typical aftermarket part BS
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      10-29-2012, 06:19 PM   #25
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Quote:
Originally Posted by bigjae1976 View Post
Typically in an E46 (suspension design is not that different, right?), most run the biggest front bar possible and a smallish rear bar. Some even skip using a rear bar..all in the name to banish understeer. Sheesh, Turner sells a 40mm front bar. If the normal thinking were to hold true, wouldn't a 40mm bar render your steering wheel useless?

I think the main difference with the E9X is that you don't have to do nearly as much to get the car close to neutral.
E46 front suspension is very different from the E9x, as different as two mcpherson strut setups can be anyway. Take a look at the knuckle design and the lower control arms. The correct answer on an E9x doesn't appear to be to stop the suspension from moving so it can't screw up the tires, though if you're stuck with soft spring rates for whatever reason, a stiffer front bar does help
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      10-31-2012, 12:02 PM   #26
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All this obsession about bars...It's the LEAST of your concerns IMO.

A wise man once told me, suspension components impact handling in the following way:

Tires > Alignment > Springs > Shocks > Swaybars. Each one on the list has DIMINISHING returns in what it does for a suspension and how it can affect state of balance. Tires, obviously, has the biggest impact on how the car handles. In fact, I would guesstimate that 90% of all your handling ills can be cured by making sure you have the right size tires front and back. And since Alignment will affect the static and dynamic contact patch of the tires, it has the next biggest impact on a car's handling characteristics. In fact, I would say the two together will cure 99% of your handling ills. Then comes springs and shocks.

Heck, if you have springs of sufficient stiffness and shocks capable of handling said springs, you can even run WITHOUT front and rear bars. But if your concern is how the car handles, fix all the other parameter FIRST before worrying about the swaybars. Set your car's tire size, pressure, alignment, spring rate, and damper settings all up to get you to the ideal settings based on your style of driving, then if you still need to fine-tune the car's balance, and by fine-tune I mean you're having a rip roaring time at the track, and you notice that the front end still plows a little too early at more than half the turns at exit? Change the swaybar or its stiffness settings to see if it solves the problem.

But to obsess about swaybar settings before any other parameter is dialed in, IMO, is a waste of time.
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      10-31-2012, 03:23 PM   #27
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Quote:
Originally Posted by Richbot View Post
E46 front suspension is very different from the E9x, as different as two mcpherson strut setups can be anyway. Take a look at the knuckle design and the lower control arms. The correct answer on an E9x doesn't appear to be to stop the suspension from moving so it can't screw up the tires, though if you're stuck with soft spring rates for whatever reason, a stiffer front bar does help
I'm stuck with soft dinan springs right now.
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      11-01-2012, 07:40 PM   #28
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Quote:
Originally Posted by bigjae1976 View Post
I'm stuck with soft dinan springs right now.
Are you running stock camber up front?

I was thinking of adding a streetable plate (GC was recommended over Vorschlag because the former retains the rubber bushing), perhaps in conjunction with springs. Then if that still doesn't do it, go to a front sway...

Forgot to say, I am more concerned about tire wear due to insufficient camber at the track, then managing the last bit of understeer...
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      11-01-2012, 08:16 PM   #29
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why not start with camber plates? A larger front sway may help settle the front end a bit, but I wouldnt say the m3 has inherent understeer. it seems quite easy to get the rear to rotate, and a stiffer front seems to me that it would make the rear even easier to kick out. ie, unpredictably.
it could be worth experimenting, but my take is to try to settle the camber first.
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      11-01-2012, 08:44 PM   #30
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I think I went overboard and agree with Leo95se's assessment to try JUST camber plates first. The front sway was likely unnecessary at this point.

This is just a guess...no data behind it.
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      11-01-2012, 09:14 PM   #31
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Quote:
Originally Posted by bigjae1976 View Post
I think I went overboard and agree with Leo95se's assessment to try JUST camber plates first. The front sway was likely unnecessary at this point.

This is just a guess...no data behind it.
I am running camber plates up front as my only mod. I am using -2.8 front and -1.8 rear camber settings. I also run a square wheel and tire track setup. My car feels pretty darn well balanced, no understeer here.
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      11-01-2012, 09:49 PM   #32
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Quote:
Originally Posted by CanAutM3 View Post
I am running camber plates up front as my only mod. I am using -2.8 front and -1.8 rear camber settings. I also run a square wheel and tire track setup. My car feels pretty darn well balanced, no understeer here.
I have been thinking about going back to the OEM front bar but I don't think it matters. I don't plan to drive my M3 on the track a lot so I'll just deal with it as it.
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      11-02-2012, 06:46 PM   #33
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Quote:
Originally Posted by Purple Derple View Post
I posted this in another thread:



The the HACK said, dynamic camber change is an issue with macpherson strut design. The basic effect is that as the spring compresses when you load that corner, the wheel itself goes through a camber change, first gaining camber, and then losing it as the spring goes deeper into compression. This rate of camber change can be plotted on a graph where you see can see the camber change for a given length of compression and that is called the dynamic camber curve. Peep this vid.



I have no idea what the dynamic camber curve looks like for the e9x m3, but I would guess it is among the best out there since bmw, and m division really do know how to get the macpherson strut working for them. I believe it is for these reasons: 1 the longer control arms on the m3 broaden the curve so that marginal the rate of camber change is lessened at every point. If you think about it geometrically, an arc that is had wider radius has less change in degrees for a given distance than a short one. 2. the m3 has higher control arm joints with the chassis than other bmws that suffer this problem. Higher control arm joints mean a more acute angle between the A arm and the strut, putting the majority of the suspension's travel in the camber gain part of the curve. Camber gain is better than camber loss, but it can still hurt the contact patch nevertheless. That said, no proper tube chassis race car would have this design.

Ultimately, like the HACK said, the only way to know what works is by testing it, and what works with one tire will not necessarily work with another, especially if they're very different in grip.
Very interesting thread. Great info above--animation was very informative.
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Originally Posted by bigjae1976 View Post
I used the dinan Stage III specs (front and rear) but with more front camber. I ran 39psi hot on street tires. It tends to oversteer on exit. I can throw away one session were my rears were 47psi...definitely could tell it the tire pressures were too high while I was driving it.

If I come off the track and all of the pressures are equal on all 4 corners then I can say the car does lean towards oversteer. Not a huge issue though, I just keep my foot in the throttle and DRIFT BABY! I am asian so that is totally normal.

Quote:
Originally Posted by bigjae1976 View Post
Typically in an E46 (suspension design is not that different, right?), most run the biggest front bar possible and a smallish rear bar. Some even skip using a rear bar..all in the name to banish understeer. Sheesh, Turner sells a 40mm front bar. If the normal thinking were to hold true, wouldn't a 40mm bar render your steering wheel useless?

I think the main difference with the E9X is that you don't have to do nearly as much to get the car close to neutral.
Quote:
Originally Posted by Richbot View Post
If you are on stock or near-stock spring rates, a bigger front sway bar on its own can make the car behave better in pretty much every way. This was my experience on my car with stock springs and RDSport front bar. Better off-throttle behavior, more settled in transitions, better corner exit traction. It's a good way to gain roll stiffness if you want to or are required to stay with near-stock spring rates, with no real downsides other than dealing with typical aftermarket part BS
With our cars, and stock or close-to-stock spring rates, the thinking does seem to be that a slightly bigger front anti-roll bar will help with turn-in. The following is from Dinan's website description of their Stage III suspension for the E90/92 M3:

The higher spring rates, increased suspension travel and improved suspension geometry give the M3 even more grip for faster and more predictable cornering capabilities. All of the EDC system features are maintained for cars equipped with the option. To further reduce body roll and increase turn-in, the Stage 3 suspension system includes a 28.5mm front swaybar with urethane bushing and front camber plates.


And, similarly, from Turner Motorsport's website:

BMW made a lot of changes in the front suspension for the E82 1-series and E9X 3-series. One area where they improved on past suspensions is by using hollow sway bars to reduce weight. And to further tune the handling the bar sizes were varied among each model. We have collected the various stock sizes along with an H&R M3 bar and gave it all to one of our suspension engineers to draw some direct comparisons.

All of the E9X front sway bars are interchangeable so you can pick and choose which bar will work best for your particular application. The E93 M3 cabrio bar is the largest outside diameter [28mm] - BUT it narrows down to 24mm in the middle and it's hollow. Both will reduce it's effectiveness. You can see that the stock E90/E92 M3 front bar is a straight 26.5mm throughout it's entire length. So the difference between the two is pretty small on paper. Either one would be an upgrade over the stock non-M E9X bar. But if you want the stiffest, the H&R is clearly superior because A) it's a straight 27.0mm diameter across its length, and B) it's a solid bar, not hollow, so it resists twisting a lot more.

Sway bars contribute to the overall spring rate of the suspension. Going with too large/stiff of a bar will impact the handling balance and ride, especially with stock or mild sport springs. So you don't always want to install the biggest and stiffest bar out there. Careful consideration of the rest of your suspension and even your tires is recommended. For a E9X non-M street car, with stock or sport springs, we would probably recommend a stock M3 or the E93 M3 front bar because we know it works well in this application and it's guaranteed to be an improvement with minimal downsides. If you use the H&R M3 bar on the street, you should balance it with the H&R M3 rear bar. And if you're building a track car with stiff springs, or already have an M3, the H&R bar is clearly the best choice.

H&R Front Sway Bar - E9X M3 - 27mm
52% stiffer than the factory E90/E92 M3 bar. 42% stiffer than the E93 M3 bar!
27mm straight across (not a tapered center like the E93 M3 factory bar)
Solid core, not hollow like the stock bars (better at resisting twist)
Forged, non-adjustable steel ends
Highest tensile steel strength available

The H&R for the E9X M3 is the best anti-roll bar option for the E9X M3. Don't be let down by the "small" size compared to the factory sway bar sizes - there are some big differences! We've had our in-house suspension engineers run the math and the H&R swaybar is over 52% stiffer than the factory E90/E92 M3 bar and even over 42% stiffer than the E93 M3 sway bar upgrade. There are several reasons for this - the stock sway bars are hollow (for lighter weight) and will twist more than the solid H&R bar. Also, the E93 M3 bar is often called a 28mm bar but it actually tapers down in the center to 24mm which greatly reduces its effectiveness. So if you're looking for a serious sway bar upgrade, the H&R is clearly the way to go. Note: to maintain the handling balance of the car, we recommend only using the front bar with the matching H&R rear bar or heavily revised racing suspension.
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      11-02-2012, 09:10 PM   #34
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You hit the nail on the head.. "Matching" bars!
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      11-13-2012, 07:17 AM   #35
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Just to throw some fuel on the fire. Turner were at LRP yesterday tuning their LRP M3. They were testing some custom H&R springs for that car, with only a front sway bar. I asked them about that, as I am interested, and the engineer guy I chatted to said that with M3's rear was stiff enough as stock and that adding the sway bar to the front stiffened up front end roll and improved turn-in for a little better handling on the track. I pressed him again about needing a rear sway bar too, but he said it was a a lot of trouble to put in, and you would be okay with just a front bar if you wanted to tighten body roll up. I was expecting him to insist on matched bars since his company is a supplier.
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      11-13-2012, 08:52 AM   #36
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I don't think you'll see many rear bar offerings for the masses because of the install requirements. Not sure if your avg sway bar buyer is going to go to that trouble.
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      11-13-2012, 06:28 PM   #37
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That doesn't mean it's right, just lazy..
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      11-13-2012, 07:09 PM   #38
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Quote:
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That doesn't mean it's right, just lazy..
and..?

You didn't finish your point...

I was just surprise that TMS hadn't put both front and rear on their new M3
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      11-13-2012, 07:38 PM   #39
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It's pretty common for racecars to end up with very little or no rear bar on a front engine, rear drive setup. Rear spring tends to have more influence on ride quality than front spring so a rear bar makes sense for a street car, but I'm not sure I would ever want to go stiffer than stock considering how good the highend dampers can be now
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      11-14-2012, 03:31 PM   #40
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Exactly.. Those cars are so high end with all of the other components (likely a solid rear end) that a swaybar isn't as relevant. I'm sure it's still correct from an engineering standpoint, and not sure it's all that valuable at 'our' level.
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