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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > How to make your E90 handle - an indepth look @ dynamic chassis behavior & geo



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      12-05-2016, 03:49 PM   #23
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I get 100% what you guys are saying... but now you're talking about a very specific situation. It's already know that this chassis does not respond well to being lowered agressively and it's not ideal.

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The idea is that the farther the front suspension is from its ideal ride height, the less grip you have due to camber loss. If the springs are stiff, it won't compress as much and you'll keep the tires at a more ideal camber angle for grip.
No one here is slamming their bmws for performance. Ideal is to be what? 10-15mm lower than Msport height? Maybe you should seperate the comments out regarding running a lower than ideal cog and then compensating for that with a stiff spring rate?

You can reduce said camber change by tweaking the sway bar and playing with alignment, as you suggest yourselves. This better maintains the balance of the chasis I'd think.

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The problem with the front end of the e9x (and any mac strut) is the camber curve is limited. Compress the suspension beyond a certain point and you lose camber with each additional bit of suspension compression.
You've adressed these issues by swapping in m3 control arms, running a stiffer front sway, and dialing in alignment.

Again, if you've squared up the tires, adressed camber change with a stiffer front bar, aided turn in with a custom alignment (reduced factory toe-in), and dialed in negative camber, you've offset the need to run a jacked up front spring rate (if you've maintained an ideal ride height). The car will be pretty neutral (I say this from experience of modding my 128i with a neutral spring rate and now my 135i).

At this point I can imagine a stiffer front spring could lead to limiting suspension travel and front end grip. Allowing a bit of dive on braking is what toes the front suspension out and provides the aformentioned agility of the chasis on turn in. You're offsetting this by running overly stiff front springs. But then again this also depends on driver preference.

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Also, do not take spring rates at face value. How a spring is mounted, as well as the design of the suspension will act as levers on the spring itself, so the resulting spring rate at the wheel (wheel rate) is going to be different. Even a stock E9x with the suspension frequency designed by BMW has softer rear wheel rates than front. More on wheel rates:
everything I am saying regarding a neutral f:r spring bias is assuming we are talking about effetive wheel rates not static spring rates.
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      12-05-2016, 04:36 PM   #24
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bNks334 i'm with you all the way here.
No disputes to what you write. It all comes down to what tires you run - as that is going to open doors for more aggressive braking and pads, and also will be more demanding on suspension, ultimately requiring more roll stiffness. As you'd understand, the greater the grip, the greater the requirements of the suspension - thus the need for firmer rates.

A car prepared for track is going to see higher limits and a different set of demands from street use, and as a result, because weight transfer happens much more rapidly, you need to restore some stability back into the car - thus the firmer front rates. The stock spring bias is not a be all end all - it's what BMW configured for everyone. It is the same setup that gets beat by a solid axle mustang around Laguna Seca

Regarding stiffer springs vs stiffer sways - you hit the nail on the head. Stiffer sways will keep the inherit suspension travel upon brake dive - giving you that dynamic toe out. You're going to want that in lower traction situations (say, 200tw tires), and likely you'll want that in tighter, more technical tracks. But that same setup will not work as well at the Glen, or Mosport...where you have brakezones that take you from like 140mph back down to 70mph. You don't want that front end toeing out on you as much from hard braking. Everything is a compromise. The car needs to be setup for where it is being used, and what the driver demands of it.
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      12-05-2016, 05:58 PM   #25
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I love the details! Makes for interesting reading

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      12-05-2016, 06:09 PM   #26
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Motion ratio for front E92 (maybe all E9X) is 0.96 and rear is 0.563. Which is why the wheel rates are close to neutral when running 2 times stiffer spring rates at the rear. Which most aftermarket set ups don't have. Strange
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      12-05-2016, 06:39 PM   #27
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...There is a point where any more rear spring rate is detrimental to performance. I trust we all know this

Not addressed to anyone in particular: but guys keep harping about increasing rear rate to promote oversteer. Well, on a rwd car where you can throttle steer anyways, what good is it to also have the rear end step out on you everywhere during trailing throttle situations as well? An unstable car is not a fast one.

And let's also not forget that there are a lot more things into making suspension work than spring rates alone. You can have significantly firmer front rates and maintain a softer rear end and tune the handling balance of the car with rebound settings in the shock. Or if you're really fancy, bump settings in the shock also. And if you're really fancy, you likely can afford a proper coilover setup with custom rates and valving. And let's not forget tire pressures, and alignment. A quality shock is much more beneficial to performance than any sort of "ideal" spring rate anyhow - it is precisely why people shell out big bucks for Penske's and the like. If shopping for coilovers, I would not stop just at spring rates alone.

As for why aftermarket coilovers are configured this way - some just do it out of laziness (see eibach spring rates on their multi-pro r2 coilovers and you will see what i mean). However, some are actually tested on a 7 post shaker machine (see: KW, Bilstein) which imposes virtual loads on the suspension through a hydraulic platform which simulates whatever track surface and configuration they need. I wouldn't throw some spring rates out the window just because they do not match the front to rear spring rates on the factory e90.
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      12-05-2016, 07:31 PM   #28
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Quote:
Originally Posted by boro92 View Post
However, some are actually tested on a 7 post shaker machine (see: KW, Bilstein) which imposes virtual loads on the suspension through a hydraulic platform which simulates whatever track surface and configuration they need. I wouldn't throw some spring rates out the window just because they do not match the front to rear spring rates on the factory e90.
Was the car kw tested already modified in the ways discussed here?

I only continue the conversation because I'm still trying to learn all this and bouncing ideas off people helps.

Stock car is tremendously underspring off the factory floor. There's no question stock spring rate is too low for performance driving and more traction. A 3400lb 135i msport has an effective wheel rate of 110lb/in f:r off the factory floor (1.2hz). A 2700lb economy car comes with effective wheel rates higher than that lol. A 3400lb car will easily take advantage of an effective wheel rate of 250+lb/in. That means an 800lb spring in the rear to achieve 1.8xhz...

The heart of my personal issue is, what am I really gaining, or attempting to accomplish, by stiffening up the front springs relative to the rear? Im modified as seen in my signature...

Can anyone speculate on the advantage/disadvantages there would be for me, given my particular mods, running 500/1000 springs vs 330/1000 (1.99hz/2.10hz or an effective spring rate of close to 300lb/in)? Car is aligned to front 0 toe/-1.5* and .15 toe-in/-1.6*
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      12-05-2016, 07:46 PM   #29
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This is all so very interesting. I autox my car and only have M3 front sway(E90), M3 front arms, and rear subframe bushing inserts. I also have 0 toe/-1.5 front and .17 toe/-1.6 rear. I have MSport suspension from BMW and find it handles well with all nannies off but I know I Can get more control. I am looking at going square 8.5"x17" all the way around coming from a 8" front and 8.5" rear factory 17" rims.

Question is what am I missing? What can I do to get better handling without going full crazy race setup, I do DD this car as well and my G/F already get car sick easily.
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      12-06-2016, 11:50 AM   #30
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ccording to this post the e90 M3 rear does the opposite than regular e90

http://www.m3post.com/forums/showthr...=768539&page=2

Car will TOE OUT under squat, car will TOE IN when braking or diving and the rear end goes up.
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      12-06-2016, 11:58 AM   #31
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Quote:
Originally Posted by marconi118 View Post
ccording to this post the e90 M3 rear does the opposite than regular e90

http://www.m3post.com/forums/showthr...=768539&page=2

Car will TOE OUT under squat, car will TOE IN when braking or diving and the rear end goes up.
I think the 2nd poster has got it wrong.
James Clay even mentions: "The only time we have messed with exotic toe settings was combined with Motorsport geometry where we could get rid of a bit of the anti and move the toe link point to induce rear steer, which made the toe in under braking, out (or straight) under squat, and steered the car with roll."

IE: they have to physically change the hard mounting point of the toe link to make the rear end toe-in under braking. Which to his point, produces roll steer, as the more the back end rolls, the more the outside rear wheel points inwards (which btw - is when you'd also want a softly sprung back end!).

A stock E9x will toe-out under braking, so that under roll the rear axle understeers (the outside wheel toes out as it rolls, to combat the rear axle from steering when it's compressed).

In short, unless you modify the fixed mounting point, a stock e9x will be loose under braking but stable on power. This toe change is also seen when you lower the car. Anyone who has lowered an E90 will see - you throw it on an alignment rack, and your once normal rear toe has suddenly toe-d in a lot due to the decreased ride height. It's why they make rear toe links in the first place - because the car gets too much rear toe when you lower it.
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      12-06-2016, 12:00 PM   #32
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Quote:
Originally Posted by bNks334 View Post
Was the car kw tested already modified in the ways discussed here?

I only continue the conversation because I'm still trying to learn all this and bouncing ideas off people helps.

Stock car is tremendously underspring off the factory floor. There's no question stock spring rate is too low for performance driving and more traction. A 3400lb 135i msport has an effective wheel rate of 110lb/in f:r off the factory floor (1.2hz). A 2700lb economy car comes with effective wheel rates higher than that lol. A 3400lb car will easily take advantage of an effective wheel rate of 250+lb/in. That means an 800lb spring in the rear to achieve 1.8xhz...

The heart of my personal issue is, what am I really gaining, or attempting to accomplish, by stiffening up the front springs relative to the rear? Im modified as seen in my signature...

Can anyone speculate on the advantage/disadvantages there would be for me, given my particular mods, running 500/1000 springs vs 330/1000 (1.99hz/2.10hz or an effective spring rate of close to 300lb/in)? Car is aligned to front 0 toe/-1.5* and .15 toe-in/-1.6*
Post up an in-car driving vid where we can see the steering inputs when you are on track. That will very clearly indicate whether you need more front spring or not (as well as alignment changes).
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      12-06-2016, 12:30 PM   #33
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Quote:
Originally Posted by boro92 View Post
I think the 2nd poster has got it wrong.
James Clay even mentions: "The only time we have messed with exotic toe settings was combined with Motorsport geometry where we could get rid of a bit of the anti and move the toe link point to induce rear steer, which made the toe in under braking, out (or straight) under squat, and steered the car with roll."

IE: they have to physically change the hard mounting point of the toe link to make the rear end toe-in under braking. Which to his point, produces roll steer, as the more the back end rolls, the more the outside rear wheel points inwards (which btw - is when you'd also want a softly sprung back end!).

A stock E9x will toe-out under braking, so that under roll the rear axle understeers (the outside wheel toes out as it rolls, to combat the rear axle from steering when it's compressed).

In short, unless you modify the fixed mounting point, a stock e9x will be loose under braking but stable on power. This toe change is also seen when you lower the car. Anyone who has lowered an E90 will see - you throw it on an alignment rack, and your once normal rear toe has suddenly toe-d in a lot due to the decreased ride height. It's why they make rear toe links in the first place - because the car gets too much rear toe when you lower it.
So toe-in under acceleration and toe-out under braking. I said this and was corrected. I was told that is only for FWD.
http://www.e90post.com/forums/showpo...6&postcount=28
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      12-06-2016, 01:20 PM   #34
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Originally Posted by feuer View Post
So toe-in under acceleration and toe-out under braking. I said this and was corrected. I was told that is only for FWD.
http://www.e90post.com/forums/showpo...6&postcount=28
Take a look at this. I think those forum guys are just going off conjecture rather than what is observed when altering ride height.
My alignment - this is from changing out the lowering springs and putting back stock springs. Note the rear toe post change. It went crazy toe out with the increase in ride height. The car goes toe-in under compression and toe-out under extension. Confirmed by alignment rack. Double confirmed by James Clay, who mentioned he was only able to accomplish the opposite of this with a change in how the toe links are mounted.

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      12-06-2016, 01:28 PM   #35
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Originally Posted by tdavis42 View Post
Question is what am I missing? What can I do to get better handling without going full crazy race setup, I do DD this car as well and my G/F already get car sick easily.
Where do you feel the car lacks?
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      12-06-2016, 02:02 PM   #36
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Firstly, the above alignment is achieved all on stock xDrive ride height (I am on stock springs). The only suspension modifications to the car are Vorslag camber plates and Bilstein B8 shocks. The latter is important. Bilstien B8 shocks are shortened shock bodies with also reduced shock stroke. I run these on stock springs for a couple reasons. The obvious one is firmer bump travel and a significant boost in rebound. There is simply much improved body control with these shocks. The less obvious reason is reduced suspension droop. Suspension droop is a big factor in tuning how the car handles. Droop is defined as how much the wheel can extend downwards beyond the stock ride height. IE: Notice when you jack up the car, the wheel has a lot of downward travel? This is droop. Droop determines how grip is maintained on both front and rear axles to a degree. Consider this: When you accellerate, the rear end squats. But also, the front end lifts. In extreme situations, reduced droop will reduce front end rise under accelleration, which as you can imagine, will affect how the front tires grip in these situations. But what's more is that if the front end rises less during hard accellerations, this also means weight transfer happens more quickly between front to rear - it simply takes less time for the rear end to squat and load up the rear tires. In a dynamic driving situation, one can load up whichever end of the car more quickly to manage weight balance - which is a great advantage on the track. What's more, reduced droop also helped me pick up the inside rear tire during cornering. Yes, you read that right. A BMW is picking up the inside rear tire during cornering. What's this mean? It means a lot of weight is transfered to the nose of the car, helping generate more mechanical grip (to a degree - and in very specific situations, which is beyond the scope of this post. But hear me out), and ultimately helping the car rotate on corner entry.
I'm interested in your outlook on suspension droop. I made a thread a while ago, and people basically told me I was an idiot for worrying about droop. I'm not sure that pursuing limited droop on the front axle is the best way of going about things. With our xDrive suspensions, we're already limited in total travel, and our suspension is shifted up a bit too, so in comparison to a RWD car, we've got roughly the same bump travel, but less droop.

With the B8's, you're limiting the droop travel even further. When your on the throttle then, you're taking grip away from the front, and I would think that it would result in late corner understeer just as you're getting on the power. Its fairly easy to drive around corner entry understeer (trail braking), but if your car wants to push wide on corner exit, that means you've got to wait longer to add throttle.

Wouldn't a more effective way to speed weight transfer be to increase overall spring rate? Maybe run a longer, stiffer bumpstop in the rear? Decreased front rebound and rear compression damping and increased front compression and rear rebound?

Quote:
Originally Posted by boro92 View Post

The best thing to do here to really make the car a precision machine is to insert some full aluminum subframe bushings in the back. Turner, RE and Bimmerworld make these.
I'm interested in these, mostly just from a durability standpoint--I don't want to ever have to replace those suckers once I've done them the first time. I worry a bit about the chassis attachment points though. The E46 cars have cracking problems, I'd hate to encounter something similar on our vehicles. I also haven't heard from anyone who is running them, it seems like only race teams are using them.
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      12-06-2016, 10:25 PM   #37
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Quote:
Originally Posted by rothwem View Post
Where do you feel the car lacks?
Not sure yet......just got the increased power upgrades done on the car and we will see what it feels like at the next autox event. I wanted to get the handling a little more dialed in before adding more power. THe way the car drove stock was alright but I knew adding more power without a way to handle it was stupid. I think I will like the handling the way it is but I know I will be due for shocks soon as I just hit 80k on originals.

I'm also getting new rear tires tomorrow so that will really help.
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      12-07-2016, 12:02 PM   #38
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Quote:
Originally Posted by rothwem View Post
I'm interested in your outlook on suspension droop. I made a thread a while ago, and people basically told me I was an idiot for worrying about droop. I'm not sure that pursuing limited droop on the front axle is the best way of going about things. With our xDrive suspensions, we're already limited in total travel, and our suspension is shifted up a bit too, so in comparison to a RWD car, we've got roughly the same bump travel, but less droop.

With the B8's, you're limiting the droop travel even further. When your on the throttle then, you're taking grip away from the front, and I would think that it would result in late corner understeer just as you're getting on the power. Its fairly easy to drive around corner entry understeer (trail braking), but if your car wants to push wide on corner exit, that means you've got to wait longer to add throttle.

Wouldn't a more effective way to speed weight transfer be to increase overall spring rate? Maybe run a longer, stiffer bumpstop in the rear? Decreased front rebound and rear compression damping and increased front compression and rear rebound?



I'm interested in these, mostly just from a durability standpoint--I don't want to ever have to replace those suckers once I've done them the first time. I worry a bit about the chassis attachment points though. The E46 cars have cracking problems, I'd hate to encounter something similar on our vehicles. I also haven't heard from anyone who is running them, it seems like only race teams are using them.
You're right on the droop.
I did it just to hasten weight transfer. Yes, less front droop means less on-power steering. I accepted that compromise, as this is an awd car. It understeers on power anyway, and I can deal with the reduced on power steering issue via sway bars (rear) and tire pressures to keep the balance. I opted to hasten weight transfer so that the balance of the car can be adjusted more quickly (read: i can take weight off the nose quickly, but i can also put weight back on the nose quickly). It makes the car more tossble for trail braking and more quick to rotate when on the brakes--I'm consciously choosing to be able to weight the axles quicker at the expense of on power front-axle grip. Certainly, that can very from driver to driver (it is a driver preference thing). So I can see it go either way. Yes, there is on power push, but it's no where as bad as an fwd car and easily managed with the alignment (read: a loose one) which I run. The other factor to consider is the stock xdrive springs rock a ton of spring preload. The nose lifts at the slightest touch of the throttle. Having more droop here will slow weight transfer and improve front axle grip, yes. But I have the car rotating so much through some corners already that I haven't found the need for the extra droop. My tune may change if I had more buttoned down suspension setup (read: coilovers), but I do not. Soft stock springs....I want some quick weight transfer

Regarding the alloy bushings - I did a lot of research on this also. No chassis tearing noted on e9x, even with r comps etc and these mods being done to M3s (which are of course, way way way faster than my 328).

You're also right on the rebound, spring rates etc. However, I'm on an xdrive and there are no real performance options with awd unfortunately. I am stuck with stock springs and I am on Bilstein shocks. No adjustments as you know.
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      12-07-2016, 04:53 PM   #39
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Quote:
Originally Posted by boro92 View Post
You're also right on the rebound, spring rates etc. However, I'm on an xdrive and there are no real performance options with awd unfortunately. I am stuck with stock springs and I am on Bilstein shocks. No adjustments as you know.
There are actually some options, TC Kline is most common, but there is someone who has JRZs if you are willing to put down $3k+.
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      12-07-2016, 08:32 PM   #40
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Can anyone comment on the aforementioned ideal M-sport ride height and what it's supposed to look like on a rwd E92 coupe? Is the fender gap supposed to be the same front to rear? How much fender gap roughly? My car came with sport suspension originally and there was definitely a higher gap in front than the rear (stock sport) if I remember correctly which I always thought was due to U.S. regulations concerning ride height/pedestrians but maybe not. I now have KW clubsports and want to have them set to optimal ride height for high speed stability/handling vs outright traction; right now I have an almost 2-finger gap in front and almost a one finger gap in the rear. One thing I like about it this way is that it kind of levels the car out so it doesn't look like it's going downhill on level ground...do i need to raise the rear though to match the front (I don't have adjustable toe arms but am open to them)? Or raise both ends? Here's a pic of how my car sits....this is with 18" wheels by the way, M3 upper and lower control arms front and rear, and getting ready to slap on front and rear H&R sway bars. Sadly I haven't really taken advantage of my camber plates yet either, they are set right in the middle though I do have my shock tower pins pulled and last alignment I came away with neg 2 deg camber in both front and rear either side, .15 total toe (.07 and .08) in front and .17 total toe in rear (.09 and .08).....kind of weird that neg camber was pretty much the same front and rear, not sure that's ideal. I do plan on adjusting the front camber plates soon though for more neg camber in front....I guess what I'm trying to say is with these settings/parts and maybe a bit more front neg camber soon, what's my ideal ride height weighted toward high speed stability/handling? Or do I need to re-think my alignment first?
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      12-07-2016, 10:25 PM   #41
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Originally Posted by nikitino25 View Post
Can anyone comment on the aforementioned ideal M-sport ride height and what it's supposed to look like on a rwd E92 coupe? Is the fender gap supposed to be the same front to rear? How much fender gap roughly? My car came with sport suspension originally and there was definitely a higher gap in front than the rear (stock sport) if I remember correctly which I always thought was due to U.S. regulations concerning ride height/pedestrians but maybe not. I now have KW clubsports and want to have them set to optimal ride height for high speed stability/handling vs outright traction; right now I have an almost 2-finger gap in front and almost a one finger gap in the rear. One thing I like about it this way is that it kind of levels the car out so it doesn't look like it's going downhill on level ground...do i need to raise the rear though to match the front (I don't have adjustable toe arms but am open to them)? Or raise both ends? Here's a pic of how my car sits....this is with 18" wheels by the way, M3 upper and lower control arms front and rear, and getting ready to slap on front and rear H&R sway bars. Sadly I haven't really taken advantage of my camber plates yet either, they are set right in the middle though I do have my shock tower pins pulled and last alignment I came away with neg 2 deg camber in both front and rear either side, .15 total toe (.07 and .08) in front and .17 total toe in rear (.09 and .08).....kind of weird that neg camber was pretty much the same front and rear, not sure that's ideal. I do plan on adjusting the front camber plates soon though for more neg camber in front....I guess what I'm trying to say is with these settings/parts and maybe a bit more front neg camber soon, what's my ideal ride height weighted toward high speed stability/handling? Or do I need to re-think my alignment first?
In regards to high speed stability, lower is better to a degree. Less air going under the car = less front end lift = more high speed stability. Toe in brings stability, as well as aero like flat undertray, splitter, wing, hood vent etc.
Once you get going fast, the steering on a stock car becomes noticeably lighter, which is kind of scary...
Unless you get the spherical fully adjustable control arms w/ spacers from Bimmerworld(James clay doesn't even recommend these on a street car), you're always going to have to compromise between outright mechanical grip/correct geometry, stability, and responsiveness. Even then, you're still going to have to make compromises. I went down the rabbit hole of looking at the front suspension geometry a while ago, and came to the conclusion that unless you are competitively racing the car, it really doesn't matter. There's no need to re-invent the wheel. Hundreds of people are perfectly happy(and fast) using much higher front wheel rates than rear, and significantly lowering the entire car.
Experiment with the ride height a little. My JRZ's hated being close to OEM m-sport height, and when I lowered the car a little, they started working much better. I would think clubsports would like to be low.
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      12-08-2016, 03:33 AM   #42
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Thanks, my immediate plan is to raise the rear slightly to get it closer to oem m-sport height when I install my rear H&R swaybar one reason being that I don't currently have adjustable rear sway links nor toe arms and feel like things will line up better this way. It's a real pain to make ride height adjustments in the rear with the KW's though, the easiest way is to take out the spring which means disconnecting the upper or lower shock. Well the easiest way would be having the special BMW spring compressor tool but no dice on that. How do you like the jrz's on the street by the way?
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      12-08-2016, 07:58 AM   #43
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M3 rear subframe has longer toe arm than regular e90

will this increase or reduce toe variation in compression?

Asking because I am running M3 subframe on my 335i
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      12-08-2016, 09:29 AM   #44
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It should be noted that KW clubsport is provided with documentation which provides a ride height guide. The KW struts are not the most robust, and need to be run in the ride height ranges specified in the manual.

That said, the car pictured is raked forward (albeit less than factory), which is what you want. It moves the roll centers to a more ideal place compared to the factory configuration. Dropping the rear down (to equal or close ride height to the front) will assist with corner exit grip due to the bump-toe characteristics of the rear axle. That said, it also depends on the circuit(s) you are frequenting. The ground surface will also dictate if you have enough bump travel or not. Is the car corner balanced?

Also, what sort of behavior are you experiencing on entry and exit of corners? I'm assuming that since we're talking about rear axle height, you are addressing something (perhaps loose on entry and cannot get enough power down on exit?).
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