ARMA SPEED
BMW Garage BMW Meets Register Search Today's Posts Mark Forums Read

Go Back   BMW M3 and BMW M4 Forum > BMW F80 M3 / F82 M4 Technical Topics > Suspension | Brakes | Chassis

Post Reply
 
Thread Tools Search this Thread
      03-31-2021, 01:34 PM   #1
slaughter.mode
Major
slaughter.mode's Avatar
United_States
881
Rep
1,044
Posts

Drives: 2018 M4 Competition
Join Date: Mar 2018
Location: Chino Hills, California

iTrader: (0)

Garage List
2018 BMW M4 ZCP  [9.80]
Excentric Control Arm Bushing Upgrades?

Anyone ever use these? Description is: Reposition the rear control arm for lowered cars.

Not really sure what the benefit is with doing so.
Appreciate 0
      03-31-2021, 06:20 PM   #2
x.shell
▆ ✚✚   ▆▆▆▆▆▆
x.shell's Avatar
6577
Rep
5,304
Posts

Drives: ▋ ▉▉
Join Date: Nov 2012
Location:  ▆▆▆ ▆▆▆ ▆

iTrader: (3)

Have you ever been to a party and you casually ask a guy, "Hey, so what do you think about Chris Pine as Captain Kirk?" And you get a machine gun barrage of information detailing the history of Star Trek right up to the contemporary version of the movie opening up a worm hole of multiple parallel universes where Spock eventually finds Darth Vader and kills him before he destroys the Jedi Temple?

Anyways, in a nut shell, it has to do with suspension geometry/roll center/scrub radius. The function of that eccentric bushing adjustability goes hand in hand with every other adjustable aspect of suspension geometry, alignment, wheels, and tires.

If you post this question in the track forum, you'll probably get some very informed answers along with a bar fight (just kidding. maybe).
Appreciate 1
irunalot1515.50
      03-31-2021, 06:50 PM   #3
dvq
First Lieutenant
dvq's Avatar
United_States
319
Rep
317
Posts

Drives: 2018 M4 Competition
Join Date: Nov 2019
Location: Mountain View, CA

iTrader: (1)

Quote:
Originally Posted by the_ghost View Post
Anyone ever use these? Description is: Reposition the rear control arm for lowered cars.

Not really sure what the benefit is with doing so.
So my understanding is that when you lower your car, you basically invert the control arm — instead of it being nearly horizontal the control arm now has a downward sloping angle from your hub to the chassis.

Effectively this does two things: 1.) it lowers your roll center away from the center of gravity of the car — this has an effect of increasing the moment arm of that axle and induces more roll in your car. You typically fix this with stiffer springs or swaybars but that also leads to a less comfortable ride. 2.) as the control arm has a downward sloping angle and during a turn your wheel compresses, your tire gets less negative camber increases (not sure about this one).

When you use this eccentric bushing, you are effectively changing the mounting point of the control arm to the hub so that you can lower where it mounts instead of dead center of the bushing. This in effect changes the angle of the control arm, the roll center, and shortens the roll arm, and you get less roll.

The same applies to the front of the car but that's usually done with bumpsteer correcting adjustable tie rods and bumpsteer correcting adjustable lower control arms. The front is a little more complex since you have to fix the motion of all the control arms including the tie rods so they are parallel to each other or they will actually start steering the car when you compress the wheel — hence bumpsteer.

Anyone feel free to correct anything I've said wrong or add to it. I'm not an expert at this.
Appreciate 1
irunalot1515.50
      03-31-2021, 08:53 PM   #4
irunalot
Captain
United_States
1516
Rep
818
Posts

Drives: Porsche Carrera S
Join Date: Oct 2020
Location: Miami

iTrader: (0)

I'm definitely interested in how these can be utilized and properly configured.
Appreciate 0
      03-31-2021, 09:42 PM   #5
slaughter.mode
Major
slaughter.mode's Avatar
United_States
881
Rep
1,044
Posts

Drives: 2018 M4 Competition
Join Date: Mar 2018
Location: Chino Hills, California

iTrader: (0)

Garage List
2018 BMW M4 ZCP  [9.80]
Quote:
Originally Posted by x.shell View Post
Have you ever been to a party and you casually ask a guy, "Hey, so what do you think about Chris Pine as Captain Kirk?" And you get a machine gun barrage of information detailing the history of Star Trek right up to the contemporary version of the movie opening up a worm hole of multiple parallel universes where Spock eventually finds Darth Vader and kills him before he destroys the Jedi Temple?

Anyways, in a nut shell, it has to do with suspension geometry/roll center/scrub radius. The function of that eccentric bushing adjustability goes hand in hand with every other adjustable aspect of suspension geometry, alignment, wheels, and tires.

If you post this question in the track forum, you'll probably get some very informed answers along with a bar fight (just kidding. maybe).
Quote:
Originally Posted by dvq View Post
So my understanding is that when you lower your car, you basically invert the control arm — instead of it being nearly horizontal the control arm now has a downward sloping angle from your hub to the chassis.

Effectively this does two things: 1.) it lowers your roll center away from the center of gravity of the car — this has an effect of increasing the moment arm of that axle and induces more roll in your car. You typically fix this with stiffer springs or swaybars but that also leads to a less comfortable ride. 2.) as the control arm has a downward sloping angle and during a turn your wheel compresses, your tire gets less negative camber increases (not sure about this one).

When you use this eccentric bushing, you are effectively changing the mounting point of the control arm to the hub so that you can lower where it mounts instead of dead center of the bushing. This in effect changes the angle of the control arm, the roll center, and shortens the roll arm, and you get less roll.

The same applies to the front of the car but that's usually done with bumpsteer correcting adjustable tie rods and bumpsteer correcting adjustable lower control arms. The front is a little more complex since you have to fix the motion of all the control arms including the tie rods so they are parallel to each other or they will actually start steering the car when you compress the wheel — hence bumpsteer.

Anyone feel free to correct anything I've said wrong or add to it. I'm not an expert at this.
Great feedback, that definitely seems to make sense. I am going to just buy them along with Rear inner lower uniball bushings because they're cheap and my factory rubber ones are tore up bad. The shop I'm having install them (since I have a ridiculous HoA) do have a bunch of track cars so they, I expect, should know. The sales guys, not so much.
Appreciate 0
      03-31-2021, 09:52 PM   #6
chrisjguzman
Apex Junky
chrisjguzman's Avatar
No_Country
94
Rep
110
Posts

Drives: 2016 YMB F80 ,04 Vw turbo R32,
Join Date: Nov 2015
Location: Santa Clara Ca./ Las Vegas Nv.

iTrader: (0)

Rogue Engineering rear lower bushing is cheaper than Millways https://www.rogueengineering.com/Rog...air_p_284.html
__________________
2016 YMB F80 FatCat Motorsports Elite
2004 Vw Turbo.:R32 Streetwerke GT620+
1999 K2500 Suburban
2001 YZF R1
Appreciate 0
      03-31-2021, 10:50 PM   #7
dvq
First Lieutenant
dvq's Avatar
United_States
319
Rep
317
Posts

Drives: 2018 M4 Competition
Join Date: Nov 2019
Location: Mountain View, CA

iTrader: (1)

Quote:
Originally Posted by the_ghost View Post
Quote:
Originally Posted by x.shell View Post
Have you ever been to a party and you casually ask a guy, "Hey, so what do you think about Chris Pine as Captain Kirk?" And you get a machine gun barrage of information detailing the history of Star Trek right up to the contemporary version of the movie opening up a worm hole of multiple parallel universes where Spock eventually finds Darth Vader and kills him before he destroys the Jedi Temple?

Anyways, in a nut shell, it has to do with suspension geometry/roll center/scrub radius. The function of that eccentric bushing adjustability goes hand in hand with every other adjustable aspect of suspension geometry, alignment, wheels, and tires.

If you post this question in the track forum, you'll probably get some very informed answers along with a bar fight (just kidding. maybe).
Quote:
Originally Posted by dvq View Post
So my understanding is that when you lower your car, you basically invert the control arm — instead of it being nearly horizontal the control arm now has a downward sloping angle from your hub to the chassis.

Effectively this does two things: 1.) it lowers your roll center away from the center of gravity of the car — this has an effect of increasing the moment arm of that axle and induces more roll in your car. You typically fix this with stiffer springs or swaybars but that also leads to a less comfortable ride. 2.) as the control arm has a downward sloping angle and during a turn your wheel compresses, your tire gets less negative camber increases (not sure about this one).

When you use this eccentric bushing, you are effectively changing the mounting point of the control arm to the hub so that you can lower where it mounts instead of dead center of the bushing. This in effect changes the angle of the control arm, the roll center, and shortens the roll arm, and you get less roll.

The same applies to the front of the car but that's usually done with bumpsteer correcting adjustable tie rods and bumpsteer correcting adjustable lower control arms. The front is a little more complex since you have to fix the motion of all the control arms including the tie rods so they are parallel to each other or they will actually start steering the car when you compress the wheel — hence bumpsteer.

Anyone feel free to correct anything I've said wrong or add to it. I'm not an expert at this.
Great feedback, that definitely seems to make sense. I am going to just buy them along with Rear inner lower uniball bushings because they're cheap and my factory rubber ones are tore up bad. The shop I'm having install them (since I have a ridiculous HoA) do have a bunch of track cars so they, I expect, should know. The sales guys, not so much.
Make sure they know what they're doing when setting up the eccentric offset bushings, I would take it to nobody other than a speciality shop that has experiencing in roll center adjustment etc.
Appreciate 0
      04-05-2021, 07:29 PM   #8
irunalot
Captain
United_States
1516
Rep
818
Posts

Drives: Porsche Carrera S
Join Date: Oct 2020
Location: Miami

iTrader: (0)

I ended up ordering the Milway bushings as I'm also using the SPL Front Lower Control Arm to fix the roll center.

I'm having front arms, rear bushing and MCS 3 ways installed next week and will report back after its complete
Appreciate 0
      04-05-2021, 07:33 PM   #9
slaughter.mode
Major
slaughter.mode's Avatar
United_States
881
Rep
1,044
Posts

Drives: 2018 M4 Competition
Join Date: Mar 2018
Location: Chino Hills, California

iTrader: (0)

Garage List
2018 BMW M4 ZCP  [9.80]
Quote:
Originally Posted by dvq View Post
Make sure they know what they're doing when setting up the eccentric offset bushings, I would take it to nobody other than a speciality shop that has experiencing in roll center adjustment etc.
Quote:
Originally Posted by irunalot View Post
I ended up ordering the Milway bushings as I'm also using the SPL Front Lower Control Arm to fix the roll center.

I'm having front arms, rear bushing and MCS 3 ways installed next week and will report back after its complete
Awesome. I don't expect a ton of difference but I am more concerned about comfortability.
Appreciate 0
      04-05-2021, 07:47 PM   #10
irunalot
Captain
United_States
1516
Rep
818
Posts

Drives: Porsche Carrera S
Join Date: Oct 2020
Location: Miami

iTrader: (0)

After the GC camber plates my car is a bit noisy over bad roads but its tolerable. I'm sure the front lower control arm will add more noise than the rear bushings, but we shall see LOL. I did end up finding and fixing all the rattles in my car and that made a massive difference. Road noise I can tolerate but rattles drive me crazy. I'd like to go to full SPL suspension but am being cautious with the noise. I will tolerate it for the ability to correct the roll center.

I'll let you know how it goes overall, hopefully its not to bad in the noise department.
Appreciate 0
      04-09-2021, 05:21 PM   #11
slaughter.mode
Major
slaughter.mode's Avatar
United_States
881
Rep
1,044
Posts

Drives: 2018 M4 Competition
Join Date: Mar 2018
Location: Chino Hills, California

iTrader: (0)

Garage List
2018 BMW M4 ZCP  [9.80]
Quote:
Originally Posted by irunalot View Post
After the GC camber plates my car is a bit noisy over bad roads but its tolerable. I'm sure the front lower control arm will add more noise than the rear bushings, but we shall see LOL. I did end up finding and fixing all the rattles in my car and that made a massive difference. Road noise I can tolerate but rattles drive me crazy. I'd like to go to full SPL suspension but am being cautious with the noise. I will tolerate it for the ability to correct the roll center.

I'll let you know how it goes overall, hopefully its not to bad in the noise department.
You get these slapped in yet?
Appreciate 0
      04-09-2021, 05:40 PM   #12
irunalot
Captain
United_States
1516
Rep
818
Posts

Drives: Porsche Carrera S
Join Date: Oct 2020
Location: Miami

iTrader: (0)

Quote:
Originally Posted by the_ghost View Post
Quote:
Originally Posted by irunalot View Post
After the GC camber plates my car is a bit noisy over bad roads but its tolerable. I'm sure the front lower control arm will add more noise than the rear bushings, but we shall see LOL. I did end up finding and fixing all the rattles in my car and that made a massive difference. Road noise I can tolerate but rattles drive me crazy. I'd like to go to full SPL suspension but am being cautious with the noise. I will tolerate it for the ability to correct the roll center.

I'll let you know how it goes overall, hopefully its not to bad in the noise department.
You get these slapped in yet?
They just arrived today and my cars is in the shop on the 15th for its new suspension.
Appreciate 0
      04-14-2021, 06:59 PM   #13
irunalot
Captain
United_States
1516
Rep
818
Posts

Drives: Porsche Carrera S
Join Date: Oct 2020
Location: Miami

iTrader: (0)

Quote:
Originally Posted by the_ghost View Post
You get these slapped in yet?
The car went into the shop this afternoon so I will have it back Friday. I did reach out to Milway to ask about the position of the bushing. They did recommend the 15 degree installation as seen below.
Attached Images
 
Attached Images
File Type: pdf 90474B Geometry.pdf (203.4 KB, 105 views)
Appreciate 0
      04-15-2021, 01:21 AM   #14
slaughter.mode
Major
slaughter.mode's Avatar
United_States
881
Rep
1,044
Posts

Drives: 2018 M4 Competition
Join Date: Mar 2018
Location: Chino Hills, California

iTrader: (0)

Garage List
2018 BMW M4 ZCP  [9.80]
Quote:
Originally Posted by irunalot View Post
The car went into the shop this afternoon so I will have it back Friday. I did reach out to Milway to ask about the position of the bushing. They did recommend the 15 degree installation as seen below.
I need to find a shop that's really versed in these type of upgrades. This diagram is great for my understanding, I'm going to find a shop. Right on!
Appreciate 0
      04-15-2021, 04:37 AM   #15
irunalot
Captain
United_States
1516
Rep
818
Posts

Drives: Porsche Carrera S
Join Date: Oct 2020
Location: Miami

iTrader: (0)

I did some digging around and found a similar part. The eccentric bushing is part of the Team Schirmer kinematics kit as well.

https://www.teamschirmerparts.com/co...s-gt-rear-axle
Appreciate 0
      05-07-2021, 06:45 AM   #16
irunalot
Captain
United_States
1516
Rep
818
Posts

Drives: Porsche Carrera S
Join Date: Oct 2020
Location: Miami

iTrader: (0)

Some interesting notes on roll center adjustment using these eccentric rear bushings and SPL front lower control arms with the supplied roll center correction spacers. Keep in mind I am also installing MCS 3WR with true rear coil overs while reading this. Although this will apply to any spring or coil-over. This particular MCS coil-over setup is supplied with 6-inch front and rear springs. But….

So now we have corrected the roll center in the rear by moving the lower control arm down and the hub up which is the desired effect of the eccentric bushing. This extends the rear damper and spring which left my rear to low with no room for adjustment with the 6-inch spring as its now to short. I need to move to a 7-inch rear spring to get the rear ride height correct and allow some room for adjustment to properly corner balance the car.

In the front you get the opposite effect as the coil-over is mounted to the hub and not the control arm. The roll center adjustment brings the hub up and the control arm down, but this now compresses the front damper and spring thus the need for a 5-inch front instead of the 6-inch.

Looking at the effect on roll center its pretty dramatic and should help overall suspension kinematics. Thats my hypothesis at least as Team Schirmer does run these eccentric rear bushings on their kinematics kit and that’s been part of their secret sauce for the M car rears. Of course, the spring rates and damper valving comes into play but I’m confident in MCS having this dialed in as well.

The shop should have the car back together after the spring changes and corner balance on Tuesday and I will report back as to the results. Only concern is the shorter damper travel in the front and is it within the correct "working range".

Anyone with more suspension feel free to chime in and add to the knowledge.

Last edited by irunalot; 05-07-2021 at 06:53 AM..
Appreciate 0
      05-07-2021, 06:53 AM   #17
slaughter.mode
Major
slaughter.mode's Avatar
United_States
881
Rep
1,044
Posts

Drives: 2018 M4 Competition
Join Date: Mar 2018
Location: Chino Hills, California

iTrader: (0)

Garage List
2018 BMW M4 ZCP  [9.80]
Quote:
Originally Posted by irunalot View Post
Some interesting notes on roll center adjustment using these eccentric rear bushings and SPL front lower control arms with the supplied roll center correction spacers. Keep in mind I am also installing MCS 3WR with true rear coil overs while reading this. Although this will apply to any spring or coil-over. This particular MCS coil-over setup is supplied with 6-inch front and rear springs. But….

So now we have corrected the roll center in the rear by moving the lower control arm down and the hub up which is the desired effect of the eccentric bushing. This extends the rear damper and spring which left my rear to low with no room for adjustment with the 6-inch spring as its now to short. I need to move to a 7-inch rear spring to get the rear ride height correct and allow some room for adjustment to properly corner balance the car.

In the front you get the opposite effect as the coil-over is mounted to the hub and not the control arm. The roll center adjustment brings the hub up and the control arm down, but this now compresses the front damper and spring thus the need for a 5-inch front instead of the 6-inch.

Looking at the effect on roll center its pretty dramatic and should help overall suspension kinematics. Thats my hypothesis at least as Team Schirmer does run these eccentric rear bushings on their kinematics kit and that’s been part of their secret sauce for the M car rears. Of course, the spring rates and damper valving comes into play but I’m confident in MCS having this dialed in as well.

The shop should have the car back together after the spring changes and corner balance on Tuesday and I will report back as to the results.
Great info to know. I'm becoming more concerned my B16s, which are a street oriented configuration, will be less compatible with these dynamics. I'm just going to swing by the local M track junkie shop, they have to know. Thanks for this!
Appreciate 0
      05-07-2021, 07:05 AM   #18
irunalot
Captain
United_States
1516
Rep
818
Posts

Drives: Porsche Carrera S
Join Date: Oct 2020
Location: Miami

iTrader: (0)

Quote:
Originally Posted by the_ghost View Post
Great info to know. I'm becoming more concerned my B16s, which are a street oriented configuration, will be less compatible with these dynamics. I'm just going to swing by the local M track junkie shop, they have to know. Thanks for this!
This is exactly why I moved from Bilstein B16Ds to MCS as I wanted a motorsport focused system and not a STREET sometimes track setup.
Appreciate 0
      05-07-2021, 08:13 AM   #19
irunalot
Captain
United_States
1516
Rep
818
Posts

Drives: Porsche Carrera S
Join Date: Oct 2020
Location: Miami

iTrader: (0)

Quote:
Originally Posted by the_ghost View Post
Great info to know. I'm becoming more concerned my B16s, which are a street oriented configuration, will be less compatible with these dynamics. I'm just going to swing by the local M track junkie shop, they have to know. Thanks for this!
Thank you for sharing this bushing and creating this post. If you didn't make this post I would not have gone down this rabbit hole and corrected the front and rear roll center.
Appreciate 0
      12-28-2023, 03:40 PM   #20
nevaland9
New Member
29
Rep
21
Posts

Drives: 2011 E90 M3
Join Date: May 2021
Location: New York

iTrader: (0)

I know this is an old post but has there been any update on this? I too have recently discovered kinematics and its basically been my hyper fixation for the past month or two. I also just got the two rear eccentric kits for the rear of my E9x and already have the Turner fronts but will likely purchase the Strom front knuckles at some point next year.

I think your only partially correct about the front and rear ride height change. I do believe that the rear will sit lower with the roll center correction eccentrics but i dont believe the front LCA spacers will have the same effect as the front LCAs dont apply load like the rear spring arm thus it doesnt dictate height. Now if the front shock was mounted directly to the LCA, then i do believe it would effect the ride height. This is all theoretically of course, i could be wrong about this but i dont recall having to make any height adjustments in the front from installing the front LCA spacers.

I would love an update on your impressions of the car after install, i think kinematics is a relatively new discussion and theres very limited knowledge shared on these forms on this topic.

Quote:
Originally Posted by irunalot View Post
Some interesting notes on roll center adjustment using these eccentric rear bushings and SPL front lower control arms with the supplied roll center correction spacers. Keep in mind I am also installing MCS 3WR with true rear coil overs while reading this. Although this will apply to any spring or coil-over. This particular MCS coil-over setup is supplied with 6-inch front and rear springs. But….

So now we have corrected the roll center in the rear by moving the lower control arm down and the hub up which is the desired effect of the eccentric bushing. This extends the rear damper and spring which left my rear to low with no room for adjustment with the 6-inch spring as its now to short. I need to move to a 7-inch rear spring to get the rear ride height correct and allow some room for adjustment to properly corner balance the car.

In the front you get the opposite effect as the coil-over is mounted to the hub and not the control arm. The roll center adjustment brings the hub up and the control arm down, but this now compresses the front damper and spring thus the need for a 5-inch front instead of the 6-inch.

Looking at the effect on roll center its pretty dramatic and should help overall suspension kinematics. Thats my hypothesis at least as Team Schirmer does run these eccentric rear bushings on their kinematics kit and that’s been part of their secret sauce for the M car rears. Of course, the spring rates and damper valving comes into play but I’m confident in MCS having this dialed in as well.

The shop should have the car back together after the spring changes and corner balance on Tuesday and I will report back as to the results. Only concern is the shorter damper travel in the front and is it within the correct "working range".

Anyone with more suspension feel free to chime in and add to the knowledge.
Appreciate 0
      12-30-2023, 05:22 AM   #21
irunalot
Captain
United_States
1516
Rep
818
Posts

Drives: Porsche Carrera S
Join Date: Oct 2020
Location: Miami

iTrader: (0)

You are right the front did not end up lower it was just the rear and we ended up using a longer spring to compensate for this.

The cars handling was amazing and the current owner agrees as well. Unfortunately I don’t have a baseline to test against as we did so many changes at once.

I did see a YouTube video where BimmerWorld is offering a kinematics update on the inner rear LCA to help correct the rear roll center.

I agree there is not enough information about this topic, which is an important one if you want to do things right.
Appreciate 1
M3SQRD1939.50
      12-30-2023, 10:37 AM   #22
M3SQRD
Major General
M3SQRD's Avatar
1940
Rep
5,309
Posts

Drives: E92 M3,G20 330ix,F22 240iX,F82
Join Date: Jun 2009
Location: Mid-Atlantic

iTrader: (11)

Quote:
Originally Posted by irunalot View Post
You are right the front did not end up lower it was just the rear and we ended up using a longer spring to compensate for this.

The cars handling was amazing and the current owner agrees as well. Unfortunately I don’t have a baseline to test against as we did so many changes at once.

I did see a YouTube video where BimmerWorld is offering a kinematics update on the inner rear LCA to help correct the rear roll center.

I agree there is not enough information about this topic, which is an important one if you want to do things right.
You never hear about rear roll center correction being discussed. You’re right, it’s an important suspension setup parameter.
Appreciate 0
Post Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -5. The time now is 10:37 AM.




f80post
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST