Problems with Spring Rates, Damper Setup and Alignment

[frontside0815]

Hey guys,

since i don´t know what to do next and up to date my german guys as well as another english forum did not really had good ideas or help, i thought maybe here are some knowledged guys who can help me with my Problem:

You can see my Mods in my Signature.

After each Change on my Suspension Setup my car was in a shop called rennfeder for a new alignment.

They told me, that my Standard ST XTA is too soft for the power my car is making and i should let them build a custom Setup with custom spring rates and matched dampers. I thought buying an LSD before anything else would be the better Option, since the open e-diff isnt the best but they told me to let them build a Setup first.
Since every work they did to my car before was superb and made the car Feeling so connected to the street i trusted them.

So 4 weeks ago my car went in the shop and they installed the following:

- Spring Rates of 110N/mm Front, 120N/mm Rear
- Reworked the Dampers to match the spring rates
- Canged the springs in the rear for a linear one with helper spring
- Installed PU Bushings in the toe arms, on top of the coilover and on the camber arm (only arms left without PU are the trailing arms).

After picking the car up it felt just awkward...The Feeling when cornering was good, you could feel that the Body roll was a lot less although it felt like the dampers absorbed Shocks from the street better.

BUT the straight line Performance sucked a lot: in every gear higher then 2nd the car just pulled in every direction. So bad that i was frightened going WOT because it was just unpredictable....

Luckily i know a guy at the shop and my relationship to them is quite good- so they offered me to Change the Setup back to the normal ST XTA Setup (Spring Rates 70N/mm and 80N/mm)...

I got my car back on Monday last week: for my Feeling the acceleration is a lot better, but the car still pulls in every direction giving it full throttle especially when going full throttle on a hill or going upwards.

I tried to install the left PU Bushings i had in the trailing arms yesterday- i think it made the problem a little bit better, but the car is still not really driveable and its really really dangerous.

My alignment Settings are:

Zero Toe front, -2,45 Camber
30' toe rear, -1,40 Camber (with the custom Setup we had -2,1 camber)

They just said its because of the open diff and it wont be better until i install a lsd.
I will install a lsd this year, but i still know there is a Problem, since the car did not do that before they installed the custom coilover Setup...

I plan trying some other alignment option, i think the toe has to be setted up other than with the stock bushings?
Or maybe the PU Bushings just sucks ass and they are worse then the oem?

If there is no alignment that makes the car pulling straight, i will buy some new toe arms and try that..

I will try to attach some pictures from how the axle looks now.

[John_01]

I don't know the actual cause of your instability.. but I'm suspicious of polyurethane bushings. To me, this seems more likely than a issue with springs and dampers. A good alignment shop should be able to check if there is movement in the bushings.

The spring rates of 70N/mm front, 80N/mm rear are badly designed for STA coil over system. The rear spring rate is not much different to stock, so it does not match the higher spring rate on the front. I'm also surprised they installed a coilover system with 110N/mm front, 120N/mm rear, because this is also mismatched between front and rear. The front spring rate is nearly double what it should be for a balanced setup. Can you double check those spring rate numbers?

Normally to improve the stability of the handling, the top priority should be upgrading the rear subframe bushings. On a high powered car, stock rear subframe bushings are a likely cause of handling problems. However this may not be the main issue here, because it seems the problem only occurred after the suspension work was done.

[frontside0815]

Hey John,

thanks for your answer.
The Alignment shop checked if there is movement in the PU´s and there isnt.

Concerning the spring rates:
Yes i am 100% sure, that These are the right rates. I actually called KW three times to ask for the Different spring rates of their coilovers.

The 1M/M392 has 110NM/120NM Spring Rates
The E82 135/E92 335i non M has 70NM/80NM.

I know, that the General rule is rear 50% higher then the front- but KW does not do it like that, dont ask me why. All i know is that here in Germany 90% of the trackcars on Nürburgring or other tracks i have visited are equipped with KW Clubsport coilovers and they all work very well (although the rates are that strange).

I see that i did not update my signature here:
I have PU Bushings in the subframe- they really made a big difference, after installed the wiggle of the rear was not present anymore. But now its there 100x heavier

[bNks334]

Originally Posted by frontside0815

Hey John,

thanks for your answer.
The Alignment shop checked if there is movement in the PU´s and there isnt.

Concerning the spring rates:
Yes i am 100% sure, that These are the right rates. I actually called KW three times to ask for the Different spring rates of their coilovers.

The 1M/M392 has 110NM/120NM Spring Rates
The E82 135/E92 335i non M has 70NM/80NM.

I know, that the General rule is rear 50% higher then the front- but KW does not do it like that, dont ask me why. All i know is that here in Germany 90% of the trackcars on Nürburgring or other tracks i have visited are equipped with KW Clubsport coilovers and they all work very well (although the rates are that strange).

I see that i did not update my signature here:
I have PU Bushings in the subframe- they really made a big difference, after installed the wiggle of the rear was not present anymore. But now its there 100x heavier

You may be feeling the e-diff braking a wheel as it begins to spin?

7k is pretty damn stiff on the front and 8k is barely any stiffer than stock. The rear of the car is going to oscillate 2x as much as the front. The rear will squat 2inches for every 1in the front does.... etc etc. Weight shifting around due to the imbalanced spring rates could easily cause the sensation of instability. Damping might be set too soft on the front or the rear allowing the car to bounce under load...

[frontside0815]

I really know, that you guys recommend other spring rates.
But being on track´s very often i know quite a few guys who run their BMW´s with the only purpose of being a track car-

90% of the guys are running KW Clubsports or Competition. And like i said: In the E9x and E8x Platform KW uses this rates- i cant really understand why but it seems to work well, because These cars are all running really really well.

[ShocknAwe]

Honestly I'm not sure its the spring rates. Sounds more like a blown damper or bushing deflection. Could be a sagged spring too, but you could see that with the car on a level surface.

[fe1rx]

Originally Posted by frontside0815

- Spring Rates of 110N/mm Front, 120N/mm Rear
- Canged the springs in the rear for a linear one with helper spring

I have to second the previous opinions that these spring rates do not make sense. The math is really indisputable.

I can't imagine why a helper spring would be needed at the back. That spring should never get slack enough to need one. An appropriate length rear spring with a height adjuster doesn't need a helper spring.

That said, these points are not the cause of your straight line issues, as you proved by switching springs back.

Originally Posted by frontside0815

I got my car back on Monday last week: for my Feeling the acceleration is a lot better, but the car still pulls in every direction giving it full throttle especially when going full throttle on a hill or going upwards.
If there is no alignment that makes the car pulling straight, i will buy some new toe arms and try that..

Can you put a GoPro on each side of the car, pointing back at the rear wheels?

I think what you will see is dramatic toe changes when accelerating. If so, something is worn in one of the rear control arms.

[bNks334]

Originally Posted by fe1rx

I
Can you put a GoPro on each side of the car, pointing back at the rear wheels?

I think what you will see is dramatic toe changes when accelerating. If so, something is worn in one of the rear control arms.

I think he pressed out all the stock bushings. My guess is the e-diff is braking wheels due to wheelspin. Almost impossible to figure something like this out over the internet though.

[fe1rx]

Originally Posted by bNks334

I think he pressed out all the stock bushings. My guess is the e-diff is braking wheels due to wheelspin. Almost impossible to figure something like this out over the internet though.

Wishbone, guide rod, outer camber bearing are all suspects too. They weren't changed to urethane.

My point is find out what the suspension is doing under acceleration, and that should narrow down the why.

Another point, we don't know what rear wheels and tires are being used. Rear spacers or wheel offsets that dramatically change the rear scrub radius will accentuate the tendency to dynamically rear toe change under braking or acceleration.

Bottom line though is it sounds like something in the rear suspension is "broken".

[frontside0815]

Thanks for the help guys.

fer1x: Doesnt Öhlins also use such a strange setup with 10nm more in the rear than in the front on the normal E82?

The following is modded:

Installed before giving the car to the shop:
- PU Subframe Bushings
- M3 FCA
- Guide Rod new M3 ones
- Wishbone/Upper Arm PU Bushing on the wheel side

Installed while inside the shop:
- Toe Arm: Both Sides PU
- Camber Arm: PU Bushing on the Side of the Subframe
- PU Strongflex Strut Mount

Installed after picking the car up to see if it solves the issue:
- Trailing Arm: Both Sides PU

So all Rubber Bushings were changed for PU ones. The only Rubber Bushing left is the one on the wheelcarrier side in the guide rod.
And there are no bushings left used, so i dont see how anything there could be broken?

The strange thing is:
I have been at a trackday last monday (Bilster Berg) and you don´t really notice the problems on track. I think thats because you are above max. NM all the time and you notice it the most when the engine makes most power.

During the drive home just one takeover and you noticed it again..

I tried to play around with the different damper settings:
The front and rear dampers were almost turned fully stiff- after loosening them quite a bit i again thought that it made the problem a bit better.

It is still there and the car still does not accelerate as good as before it went to the shop for the custom setup, but it´s better then when I picked it up in the beginning.

Tires are Michelin 245/35 Pilot Super Sports all around on BBS RC 303 8,5 x 18 ET38. But they were mounted before and i did not have these problems, so they are not the reason for it.

I have a shop which wants to try some other specs during alignment..maybe this helps. Then i am thinking about order the Bimmerworld Toe Arms, just to make sure, its not the PU Bushings in the Toe Arms which deflect more then the oem ones.....

I don´t have 2 gopros i think :/ but that is a really good idea! I have to see if there is a friend who can borrow me one. Will let you know!

[MightyMouseTech]

Originally Posted by frontside0815

Thanks for the help guys.

fer1x: Doesnt Öhlins also use such a strange setup with 10nm more in the rear than in the front on the normal E82?

The following is modded:

Installed before giving the car to the shop:
- PU Subframe Bushings
- M3 FCA
- Guide Rod new M3 ones
- Wishbone/Upper Arm PU Bushing on the wheel side

Installed while inside the shop:
- Toe Arm: Both Sides PU
- Camber Arm: PU Bushing on the Side of the Subframe
- PU Strongflex Strut Mount

Installed after picking the car up to see if it solves the issue:
- Trailing Arm: Both Sides PU

So all Rubber Bushings were changed for PU ones. The only Rubber Bushing left is the one on the wheelcarrier side in the guide rod.
And there are no bushings left used, so i dont see how anything there could be broken?

The strange thing is:
I have been at a trackday last monday (Bilster Berg) and you don´t really notice the problems on track. I think thats because you are above max. NM all the time and you notice it the most when the engine makes most power.

During the drive home just one takeover and you noticed it again..

I tried to play around with the different damper settings:
The front and rear dampers were almost turned fully stiff- after loosening them quite a bit i again thought that it made the problem a bit better.

It is still there and the car still does not accelerate as good as before it went to the shop for the custom setup, but it´s better then when I picked it up in the beginning.

Tires are Michelin 245/35 Pilot Super Sports all around on BBS RC 303 8,5 x 18 ET38. But they were mounted before and i did not have these problems, so they are not the reason for it.

I have a shop which wants to try some other specs during alignment..maybe this helps. Then i am thinking about order the Bimmerworld Toe Arms, just to make sure, its not the PU Bushings in the Toe Arms which deflect more then the oem ones.....

I don´t have 2 gopros i think :/ but that is a really good idea! I have to see if there is a friend who can borrow me one. Will let you know!

Stability during hard acceleration is quite often just rear toe. Need to increase toe-in in the rear.

[frontside0815]

Hey Today i set up my side mirrors so that i can see my left rear wheel during acceleration.
It seems that the tire does change toe in out direction during acceleration...

So do you think Bimmerworld Toe Arms would solve this issue?

[John_01]

- Camber Arm: PU Bushing on the Side of the Subframe

This one is a heavily loaded bushing. On the Bimmerworld website they have a spherical bearing upgrade for this as well, which they obviously recommend. I wonder if the polyurethane version is adequately stiff.

Bimmerworld toe links would probably help. I wonder if the lower camber link bushing may also be contributing to this.

If trying to identify the issue by looking in the mirror, I think its may be hard to see properly. Mostly what you see is the compression of the rear suspension.

[frontside0815]

You mean These:
http://www.bimmerworld.com/BimmerWor...aring-Kit.html ?

Fucking expensive.. Wont spend almost 300 bucks for some bushings, that is ridiculus.

And looking at powerflex and what they use for this bushings it Looks almost 100% identical to what i installed- powerflex is a well known brand and i doubt they would offer these bushings if they were that bad:

http://www.powerflex-deutschland.eu/...676520678.html

Will decide in the next days if i am gonna try the BW or other upgraded toe arms or not.

[John_01]

The rear camber arm bushing set from Bimmerworld is less expensive than the toe arms. $250 vs $290. Price is easy to judge, but what we don't know is how much deflection is reduced. Unfortunately we have no way to compare the options of Stock rubber, Spherical bushing, and Polyurethane. I agree with your assessment that Powerflex is a well known and popular brand.

[Suhb]

I know this is an unpopular opinion among these forums, but 0 toe is absolute shit on this car. Having tried 0 toe, experiencing really nice, quick steering response at the cost of serious front end instability, I dialed it back to 0.03 toe in on both sides.

This, coupled with -2.4 degrees of camber, the car's front end is still crap. What others are saying is true on some level. You need solid mounted or close to 0 flex bushings in all control arms to make 0 toe work. Every time you get on the gas, the rear pushing the front wheels makes the car gain more toe out causing instability. Braking gives the car even more toe out. All of the the instability is exaggerated by the negative camber causing the front end to dart around.

My car experiences really hard driving, auto cross but also a lot of highway miles and and I have not been satisfied at all with 0, or very small toe in at all. I am going to return the toe settings to just under factory toe in levels.

It's the nature of a streetable rear wheel drive car to gain to out in acceleration and braking. So you'll have toe out on the front end more often than not. Gauge how much stiffer your bushings are than stock, your braking G's and acceleration G's, and dial in approapriate toe in. You want the toe in to get close to 0 toe under max braking/acceleration. Toe out makes the car unstable.

Another unpopular opinion: what may give an experienced race car driver in terms of suspension setup the fastest lap time may not give you the fastest lap time. They do it for a living and drive the car on the absolute edge. Don't push the suspension set up to the cutting edge limit (especially in terms of toe) if it costs you stability. Instability and unpredictability kills your lap times until you have more experience under your belt.

[bNks334]

Originally Posted by Suhb

I know this is an unpopular opinion among these forums, but 0 toe is absolute shit on this car. Having tried 0 toe, experiencing really nice, quick steering response at the cost of serious front end instability, I dialed it back to 0.03 toe in on both sides.

This, coupled with -2.4 degrees of camber, the car's front end is still crap. What others are saying is true on some level. You need solid mounted or close to 0 flex bushings in all control arms to make 0 toe work. Every time you get on the gas, the rear pushing the front wheels makes the car gain more toe out causing instability. Braking gives the car even more toe out. All of the the instability is exaggerated by the negative camber causing the front end to dart around.

My car experiences really hard driving, auto cross but also a lot of highway miles and and I have not been satisfied at all with 0, or very small toe in at all. I am going to return the toe settings to just under factory toe in levels.

It's the nature of a streetable rear wheel drive car to gain to out in acceleration and braking. So you'll have toe out on the front end more often than not. Gauge how much stiffer your bushings are than stock, your braking G's and acceleration G's, and dial in approapriate toe in. You want the toe in to get close to 0 toe under max braking/acceleration. Toe out makes the car unstable.

Another unpopular opinion: what may give an experienced race car driver in terms of suspension setup the fastest lap time may not give you the fastest lap time. They do it for a living and drive the car on the absolute edge. Don't push the suspension set up to the cutting edge limit (especially in terms of toe) if it costs you stability. Instability and unpredictability kills your lap times until you have more experience under your belt.

I agree to some extent. I have recommended 0 toe up front several times now and I'm actually running .05* per side myself out of preference. Car feels a lot more stable than when I had it at 0. I've driven with toe-out before after making camber changes and the car was very darty for daily driving. With slight toe-in, the car doesn't "wander" under heavy braking and acceleration as much. I do think a bit of toe-out is nice for autocross cars though.

I only have m3 front arms and my car doesn't wander at all. I do also have rsfb installed. I'm sure rear toe arms and camber arms won't hurt anything though.

[frontside0815]

Just a quick update:
I am in holiday atm and my car is in another shop.
After driving the car the shop said the problem is really strange and so heavy that he doesnt think it will be solved only with a new alignment.

So what i did was ordering Bimmerworld Toe Arms. They were installed 3 days ago- without a new alignment yet the shop says the car feels 50-60% better and the problem is almost gone.

So it seems that the PU Bushings are totally garbage. I really hate it, that i now have to do everything again and change out all Arms/Bushings where the PU ones are in.

I ordered a new M3 Upper Arm, just that the shop can dismount the OEM with PU in it before doing a new alignment.

After that i will do the following:

- Buying the spherical bearing from BW for the lower camber arm, to change out for the PU Shit
- Buying the bearings from BW for the Trailing arm, to change out for the PU Shit.

When changing the Bushings from the trailing arm, a new alignment is not necessary right?
But when changing the bushing on the lower control arm where the shock connects to, the car has to be aligned again, right?

When the car handles like before, i will think about the next steps regarding the coilover setup. I trust you guys that the spring rates are not that good, thats why i will sell the ST XTA and buy something with balanced spring rates- still haven´t decided which way to go.

Anything else you would do?

Thanks again for the help guys

[Kgolf31]

Originally Posted by frontside0815

Just a quick update:
I am in holiday atm and my car is in another shop.
After driving the car the shop said the problem is really strange and so heavy that he doesnt think it will be solved only with a new alignment.

So what i did was ordering Bimmerworld Toe Arms. They were installed 3 days ago- without a new alignment yet the shop says the car feels 50-60% better and the problem is almost gone.

So it seems that the PU Bushings are totally garbage. I really hate it, that i now have to do everything again and change out all Arms/Bushings where the PU ones are in.

I ordered a new M3 Upper Arm, just that the shop can dismount the OEM with PU in it before doing a new alignment.

After that i will do the following:

- Buying the spherical bearing from BW for the lower camber arm, to change out for the PU Shit
- Buying the bearings from BW for the Trailing arm, to change out for the PU Shit.

When changing the Bushings from the trailing arm, a new alignment is not necessary right?
But when changing the bushing on the lower control arm where the shock connects to, the car has to be aligned again, right?

When the car handles like before, i will think about the next steps regarding the coilover setup. I trust you guys that the spring rates are not that good, thats why i will sell the ST XTA and buy something with balanced spring rates- still haven´t decided which way to go.

Anything else you would do?

Thanks again for the help guys

For an Autox/Track oriented car I ran 400# in the front/700# in the rear. That's still relatively soft in the grand scheme of things.

I ran -3.5* of camber up front, 0 Toe with -1.9* of camber in the rear with 14 minutes of toe in, and never had these issues like you describe.

Also, make sure shock dynos are adequate to handle the spring rates, too much/little rebound and bump can play havoc on handling issues.

[frontside0815]

Picked up my car yesterday.
Installed the BW Toe arms and M3 Upper Arm.
So PU is left on the Lower Camber arm in the inside and on the trailing arm both sides.

With Installing the BW Toe Arm the car finally drives like before! Now you can go WOT without touching the steering wheel.

Still i want to throw out that fucking PU shit everywhere- really fucked up that strongflex seem to sell shit for the arms. The PU Bushings for the Subframe really helped.

Thanks for your help!