03-31-2021, 01:34 PM | #1 |
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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. |
03-31-2021, 06:20 PM | #2 |
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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). |
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03-31-2021, 06:50 PM | #3 | |
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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. |
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03-31-2021, 09:42 PM | #5 | ||
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03-31-2021, 09:52 PM | #6 |
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Rogue Engineering rear lower bushing is cheaper than Millways https://www.rogueengineering.com/Rog...air_p_284.html
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03-31-2021, 10:50 PM | #7 | |||
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04-05-2021, 07:29 PM | #8 |
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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 |
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04-05-2021, 07:33 PM | #9 | |
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04-05-2021, 07:47 PM | #10 |
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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. |
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04-09-2021, 05:21 PM | #11 | |
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04-09-2021, 05:40 PM | #12 | ||
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04-14-2021, 06:59 PM | #13 |
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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.
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04-15-2021, 01:21 AM | #14 |
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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!
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04-15-2021, 04:37 AM | #15 |
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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 |
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05-07-2021, 06:45 AM | #16 |
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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.. |
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05-07-2021, 06:53 AM | #17 | |
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05-07-2021, 07:05 AM | #18 |
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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.
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05-07-2021, 08:13 AM | #19 |
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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.
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12-28-2023, 03:40 PM | #20 | |
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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:
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12-30-2023, 05:22 AM | #21 |
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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. |
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12-30-2023, 10:37 AM | #22 | |
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