Originally Posted by Purple Derple
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.
interesting thread. Great info above--animation was very informative.
Originally Posted by bigjae1976
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.
Originally Posted by bigjae1976
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.
Originally Posted by Richbot
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.