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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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      12-08-2016, 02:36 PM   #45
nikitino25
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Quote:
Originally Posted by boro92 View Post
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?).
KW recommends the following lowering range with Clubsports:

Front Lowering: 1.2" to 2.3"
Rear Lowering: 0.9" to 2.1"

I guess this would be down from stock ride height but the problem is that I can't remember or don't know what "stock" ride height is. From the picture, does it look like I'm in the recommended KW range? And to clarify, you're saying that less forward rake is better for the roll center?
My car is not corner balanced and I've always wondered what the front/to rear height ratio would look like on a corner balanced coupe? Anyone have a pic by chance? The main thing I'm trying to dial out is a bit of unwanted body roll when changing direction at high speeds. Hopefully my upcoming H&R bars will help mitigate this....I guess i'm just trying to get the best ride height for high speed handling if there is such a thing and now keeping within the KW lowering range. My car doesn't look lowered more than 2.3" in front and 2.1" in the rear does it?

Last edited by nikitino25; 12-08-2016 at 02:41 PM.
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      12-08-2016, 05:38 PM   #46
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No, your car doesn't look that low.
What tracks are you hitting, and do you have video?
Less forward rake is better - yes. Keeping the nose higher puts your camber curve in a more ideal spot (it loses camber beyond a certain ride height), but also keeps your roll stiffness in check geometrically and actually will affect body roll to a degree (too low will actually enhance bodyroll). Also, going too low puts all of your suspension arms in a range they were never intended to travel in frequently, and the amount of bump steer you get may be more dramatic when compared to closer to stock height. That said, I am not saying lowering is bad - you want to drop cg. How far you go is also going to be determined by how bumpy the tracks you go to are. Or if you like to hit the berms, you can slam into those bump stops which wont help you any. So adjust accordingly.

Corner balancing is going to do just that - change corner heights to alter the weight distribution in the car. It's not that the front may be higher than the rear. But more like the driver side rear is higher than the passengerside rear (and the opposite for the front). This is to account for your driver weight and other factors.

As for the rear, I'd remove the rake and drop it down to where your fronts are. More stability out of corners. look at the e90 grand am cars also - they are setup where the rears are close to front ride heights (but fender gap in rear is like none, compared to the front where there is still some).
See pic here: http://www.e90post.com/forums/attach...1&d=1248703937
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      12-08-2016, 07:27 PM   #47
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Actually I haven't tracked my car (yet) but do a lot of high speed driving down in Mexico......my car's ride height actually looks proportional to the turner car....if I raise the rear to match the front (talking fender gap here) the car would just be that much more raked forward....I think my current setup is about right then, to avoid raking the car, the front (wheel gap) needs to be higher than the rear which mine and the Turner car is...
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      12-08-2016, 07:47 PM   #48
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Quote:
Originally Posted by nikitino25 View Post
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?
Yeah, I've got adjustable toe arms and end links, so the lowering isn't a big deal. I usually disconnect the camber link to release the springs, and adjust the ride height, with HPA's ride height adjusters. It's gonna be a pita anyways, since you need an alignment afterwards. The JRZ's aren't too bad on the street. Not cloudlike, but no where near unbearable. I'm at right under the middle stiffness settings on both ends. They're little stiff at low speeds. Although I have solid shock mounts and camber plates, along with 450F 800R rates. I feel like you could make them comfortable if you tried. Body control is top notch, and bumps really don't upset the car anymore.
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      12-09-2016, 12:11 PM   #49
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I actually found a way to adjust the rears without removing the spring. With a large plumbers type vice grip wrench, you can hold the base of the adjuster so that it doesn't spin when you adjust the spanner ring with the supplied wrench. It's still not easy though....
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      12-12-2016, 12:41 PM   #50
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      12-17-2016, 07:01 AM   #51
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Nice read, thanks!

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.
Have a look on what Alpina is doing on their xdrives.
They use different spring (probably stiffer) in front, but stock dampers. In the rear they use stock springs but different dampers, also a softer sway bar.
See my findings: http://www.e90post.com/forums/showthread.php?t=1332583
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      12-23-2016, 01:54 AM   #52
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Some good information in this thread. I would suggest if the RWD guys are interested in a more in-depth and much more analytical look at the suspension of their cars, they should review FE1RX's write up on 1addicts:
http://www.1addicts.com/forums/showthread.php?t=956039

As most people know, the E8X and E9X share identical suspension in every way (on RWD E9X models) save a few rear hub parts that are mostly inconsequential.

The thread I have linked to is an SAE quality writeup and truly the most in depth proper mathematical review of our cars in existence. If you search for his username you will also find many other threads that he has started for topics like comparing control arms (M vs non-M), benefits of the M rear arms (non existent basically), etc.

Hope that helps,
Mark
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      12-24-2016, 08:58 AM   #53
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Quote:
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?
Ideal ride height is when the lower control arms are parallel to the ground +/- a few degrees. This is when most of the force from the ground goes towards moving the suspension arm vertically rather than horizontally.
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      12-27-2016, 11:25 AM   #54
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Quote:
Originally Posted by lowside67 View Post
Some good information in this thread. I would suggest if the RWD guys are interested in a more in-depth and much more analytical look at the suspension of their cars, they should review FE1RX's write up on 1addicts:
http://www.1addicts.com/forums/showthread.php?t=956039

As most people know, the E8X and E9X share identical suspension in every way (on RWD E9X models) save a few rear hub parts that are mostly inconsequential.

The thread I have linked to is an SAE quality writeup and truly the most in depth proper mathematical review of our cars in existence. If you search for his username you will also find many other threads that he has started for topics like comparing control arms (M vs non-M), benefits of the M rear arms (non existent basically), etc.

Hope that helps,
Mark
Mark, that's an awesome awesome thread. Thank you for posting
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      12-27-2016, 11:52 AM   #55
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Great read. My 335i track car is simply amazing.
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      12-28-2016, 01:17 AM   #56
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Quote:
Originally Posted by rothwem View Post
Ideal ride height is when the lower control arms are parallel to the ground +/- a few degrees. This is when most of the force from the ground goes towards moving the suspension arm vertically rather than horizontally.
I believe it would be more accurate to say ideal suspension behaviour is achieved when the lower control arms are below horizontal (which is because the car will continue to gain camber as it moves through bump travel). This is often the primary reason you see people citing the "don't lower the car too much" adage. In addition, riding the bump stops all the time is a recipe for unpredictable handling at best so in cases where people are running soft springs, this is another good reason to maintain a reasonably high ride height.

However, it is also true that the lower the ride height, the lower the centre of gravity and roll centre which results in less lateral weight transfer during cornering and more overall grip. Cars with splitters or other underbody type aerodynamics also benefit from exponential gains as the car gets lower.

As is often the case, for a street car, the "ideal ride height" is likely a compromise between the two.

-Mark
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      03-03-2017, 10:01 PM   #57
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http://www.splparts.com/products/spl...x-f8x-bmw.html

http://www.splparts.com/products/spl...t-version.html

Found these. Definitely interesting.
For all of you that are into this kind of stuff, there's alot of measurements that go into setting up these adjustable arms correctly. Using special software is the easiest way to do it. You cant just slap them on.
I want to do this, but it's just more time and money spent setting these up than is worth it on a street car. Plus you would most likely have to change out the spherical bearings every few years.
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      03-06-2017, 11:30 AM   #58
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Quote:
Originally Posted by shirtpants_ View Post
http://www.splparts.com/products/spl...x-f8x-bmw.html

http://www.splparts.com/products/spl...t-version.html

Found these. Definitely interesting.
For all of you that are into this kind of stuff, there's alot of measurements that go into setting up these adjustable arms correctly. Using special software is the easiest way to do it. You cant just slap them on.
I want to do this, but it's just more time and money spent setting these up than is worth it on a street car. Plus you would most likely have to change out the spherical bearings every few years.

WOW Great find. I hadn't seen roll center correction arms for E90, let alone repositioned tie rods to get rid of the bump steer. Those are great finds. And yes - not streetable. Those sphericals are non sealed. For what it's worth and those staying near stock height, bimmerworld and others make spherical tension rod bearings to replace the rubber ones. And the lower control arm can actually rock a spherical in there too (and someone on these boards make an eccentric delrin bushing as well!). Those with x drive get away with not touching the LCA, as it's already a balljoint. an x drive will have a fully non rubber front end with spherical tension rods and camber plates.

Those SPL parts though...That's something! Adjustable for length, RC height and the tie rods to fix bump steer. Very proper
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