Suspension help. Rear end shimmy still.

Optigrab

Corporal
Sep 19, 2018
133
You sure about that? According to RealOEM there is a 2.6kg difference between the two in favor of the non-M subframe, and that's not counting the additional bolt-on braces the M-cars have
I have called ecs and they gave me some really ridiculous weights as well. I have had two separate people tell me (one to my face) that one person can pickup the m3 subframe where as it takes two people to pickup the stock one supposed to be significantly lighter
 

Crystalline

Lurker
Sep 24, 2018
12
MA
Can some of the mentioned issue be eliminated by swapping in the m3 subframe?
I'm interested in finding out the expert opinion on this as well. If you source a M3 rear end you get some of these upgraded pieces plus the dif. I'm not sure if its better to swap things over to the 335i subframe or just bolt the m3 one up.
 
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Optigrab

Corporal
Sep 19, 2018
133
I'm interesting in finding out the expert opinion on this as well. If you source a M3 rear end you get some of these upgraded pieces plus the dif. I'm not sure if its better to swap things over to the 335i subframe or just bolt the m3 one up.
Both solutions have worked for many people. I could never get a straight answer on the amount weight savings since no one bothered to weigh the subframes.
 

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Jun 4, 2018
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Here are my thoughts on the the topic of the M3 rear subframe (and overall rear M vs Non M suspension for that matter)...

This thread posted by @Torgus is about rear end shimmy of his 335i. I'm going to add to this by saying that in general the non M rear suspension is unstable under acceleration. I continually see where lots of people have issues with this.

Variations in the road, steering inputs, etc, all apply a load to the suspension and that load can vary at any moment. If you have a lot of rubber bushings then you will have a lot of geometry changes happening, an oscillation for lack of a better word. Toe is what keeps the rear of a car stable so if the toe is constantly changing (oscillating) then the car will be unstable.

For this conversation we'll break break down toe change into two aspects: change from bushing flex AND change from the suspension moving up and down (bump/rebound) which is determined by the pickup points.

Removing bushing flex stops the oscillating of the toe change. This is good! However, BMW designed the toe setting under bump/rebound WITH bushing flex in mind. You take away the bushing flex now you take away the toe setting they were trying to accomplish. So if we look at the M3 suspension we will see that BMW changes the pickup points on the M3 subframe because they removed most of the rubber bushings elsewhere. This is why I said earlier simply putting the M3 arms and aftermarket toe arm does not get you the M3 suspension. BMW claims there is a difference in the upright pickup points, too, but I cannot confirm that right now.

So to sum up, when you accelerate, the rear squats (bump) and the toe changes. We change the bushings to ball joints. Now we accelerate, the rear squats, the toe change is different than what BMW intended. The problem is too little toe in is not good and too much toe in is not good for stability. At this point, unless we change the pickup points, the only thing we can do is change static toe settings to get stability. This is why I was saying earlier you can't use the OEM alignment specs (m or Non M) if you only change out the arms.

Therefore, I cannot confirm but it is HIGHLY likely switching to the M3 subframe will cure a lot of the instability because it controls the toe change better under squat when there are fewer bushings.

A few side notes...

The fact that the M3 subframe is 5-10lbs heavier is a moot point, it's sprung weight and below the CG of the chassis. Those who say the M3 is WAY heavier are likely talking about the entire assembly including diff and axles.

I'm in the middle of measuring and testing all of this and will certainly let everyone know over the coming weeks/months as I find answers.
 

fmorelli

Colonel
Staff member
Aug 11, 2017
2,120
Virginia
I would add one other point, though likely obvious. Regardless of how the car is used, as we crank the horsepower up on these cars, we tax the suspension design. For one, the contact patch to deal with the power, changes the geometry. Second, pushing a lot more power (both max and differential) through a suspension that was not designed to take the kinds of loads. By suspension design I don't mean geometry, necessarily, but things like durometer hardness of rubber.

Filippo
 
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Jun 4, 2018
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@fmorelli very good point. The stock HP for the 335i is 300. For the M3 it was 414. When accelerating, in stock form, the M3 will squat more because it has more power. BMW changed the lower trailing arm pickup point on the M3. Changing this pickup point changes dive during braking, or squat if under acceleration. The catch is what did BMW intend with this change? Did they intend to reduce dive under braking or reduce squat under acceleration. Once I measure I'll confirm what its doing.

Side note...
More squat either from a geometry change OR a soft spring means more suspension compression which means more toe change (possibly too much) which can lead to instability. A stiff spring means less squat which means less toe change (possibly not enough) which could also lead to instability. As we dig into this we see that there are a lot of things that can cause stability problems. Gotta find that sweet spot.
 

Rob09msport

Captain
Oct 28, 2017
1,164
Monroe CT
I cant speak to arm mounting locations but I do know it is quite a bit lighter than the stock subframe
I'm pretty sure i remember it being heavier with very few differences if you search harold at hpa did a in depth comparison between m3 and non parts including weight and strength and sub frame was not beneficial.
He lightly touched the subject of pickup points I think Barry will get us a definitive answer as when harold did his write up 400 hp was then the norm now we are wrestling with 500 and more .
 
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Just to add to the topic of geometry I'll discuss some of my findings on the front which we can then relate back to the rear.

First I'll say that typically in the past BMW designs the suspensions on the Non M cars first then refines them on the M cars. I assume they did that with the E90 but I repeat... I assume, so take it for what it is worth.

Non M front...
The front control arm has a rubber bushing where it connects to the subframe and a ball joint where it connects to the spindle. The tie rod has ball joints on both the rack and spindle connections. When you corner and put a lateral load on the suspension, the control arm becomes shorter in length as the rubber bushing deflects. Since the tie rod does not have any rubber, it stays the same length. This causes the front tire to move in the direction of toe out. Think about it as if you are looking from the top down.

There is also a toe change from compressing the suspension (bump) which is caused by different angles and lengths of the tie rod and control arm with respect to each other. Think about it as if you were looking from the front.

Now lets go and replace the control arm with the M arm that has a solid ball joint where it connects to the subframe. You no longer have the toe change from the bushing flex (think top view from above). BUT you still have toe change from the different angle and length between the tie rod and control arm (front view from above). Now your "dynamic" toe is totally different than what BMW designed to the car to have.

Lets look at the M3 front...
Where the tie rod attaches to the spindle is different than the Non M spindle. (think front view again) The tie rod is now angled different so when the suspension goes into bump, the arc the arm follows pushes the toe towards toe out more than the Non M.

BMW wants toe to be a certain spec while cornering to create stability. That is why they changed the geometry on the M3 since they changed the rubber bushings to ball joints.

The Non M Rear Suspension...
BMW moved the tie rod mounting point a few mm on the M3 front spindle compared to the Non M. In the rear, the toe arm is over 30mm shorter! There is a significant geometry change with respect to dynamic toe control compared to the Non M.

The point...
Sorry for the long winded post but I wanted to point out how important suspension geometry is even if it's just changing something a few mm.
 
Jan 5, 2018
34
South Jersey
Just to add to the topic of geometry I'll discuss some of my findings on the front which we can then relate back to the rear.

First I'll say that typically in the past BMW designs the suspensions on the Non M cars first then refines them on the M cars. I assume they did that with the E90 but I repeat... I assume, so take it for what it is worth.

Non M front...
The front control arm has a rubber bushing where it connects to the subframe and a ball joint where it connects to the spindle. The tie rod has ball joints on both the rack and spindle connections. When you corner and put a lateral load on the suspension, the control arm becomes shorter in length as the rubber bushing deflects. Since the tie rod does not have any rubber, it stays the same length. This causes the front tire to move in the direction of toe out. Think about it as if you are looking from the top down.

There is also a toe change from compressing the suspension (bump) which is caused by different angles and lengths of the tie rod and control arm with respect to each other. Think about it as if you were looking from the front.

Now lets go and replace the control arm with the M arm that has a solid ball joint where it connects to the subframe. You no longer have the toe change from the bushing flex (think top view from above). BUT you still have toe change from the different angle and length between the tie rod and control arm (front view from above). Now your "dynamic" toe is totally different than what BMW designed to the car to have.

Lets look at the M3 front...
Where the tie rod attaches to the spindle is different than the Non M spindle. (think front view again) The tie rod is now angled different so when the suspension goes into bump, the arc the arm follows pushes the toe towards toe out more than the Non M.

BMW wants toe to be a certain spec while cornering to create stability. That is why they changed the geometry on the M3 since they changed the rubber bushings to ball joints.

The Non M Rear Suspension...
BMW moved the tie rod mounting point a few mm on the M3 front spindle compared to the Non M. In the rear, the toe arm is over 30mm shorter! There is a significant geometry change with respect to dynamic toe control compared to the Non M.

The point...
Sorry for the long winded post but I wanted to point out how important suspension geometry is even if it's just changing something a few mm.
Thank you for that information regarding the suspension, very good read. I have a question. So if one changes the stock Non-M suspension. They should no longer use stock alignment specs? I ask as I have done a few things to the suspension and keep burning through rear tires. I have Eibach Springs, Bilstein shocks, Front M3 arms, aftermarket rear camber arms and Toe arms ( a friend gave them to me) and Rear Subframe Inserts. I recently noticed the Rear toe arms I had were crap and had a bunch of play( but this was one of the best upgrades to the suspension to me as in stability wise). So i ordered Some Meagan arms as they have good reviews and not much complaint about noise like with some of the higher end Toe arms. But now i wonder if maybe I just have to use different alignment specs?
 

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Jun 4, 2018
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@barry

https://www.1addicts.com/forums/showthread.php?t=1079383
https://www.1addicts.com/forums/showthread.php?t=1079383
I have to keep looking I think the key in your search is it was on reference to a 135 but I think the second link was one of a few different posts during that period.
Did you mean to post different links as they are both the same? I saw this a long time ago and what fe1rx did was awesome. His study was the difference in the structural differences between the M3 arm and the non m arm. He didn't discuss geometry at all really. I will admit I did skim it and could have missed a post where he did discuss geometry.
 

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Jun 4, 2018
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Thank you for that information regarding the suspension, very good read. I have a question. So if one changes the stock Non-M suspension. They should no longer use stock alignment specs? I ask as I have done a few things to the suspension and keep burning through rear tires. I have Eibach Springs, Bilstein shocks, Front M3 arms, aftermarket rear camber arms and Toe arms ( a friend gave them to me) and Rear Subframe Inserts. I recently noticed the Rear toe arms I had were crap and had a bunch of play( but this was one of the best upgrades to the suspension to me as in stability wise). So i ordered Some Meagan arms as they have good reviews and not much complaint about noise like with some of the higher end Toe arms. But now i wonder if maybe I just have to use different alignment specs?
I do know when you corner and put a lateral load on the rear suspension you get toe in. This creates stability. I do not know what happens to toe when you accelerate. I can pretty much assure you it toes in as well as toe out would create instability. The problem is I don't know how much it toes in under acceleration (trying to figure that out).

The problem is you have to measure the toe change dynamically, that isn't easy. Then make a bushing to ball joint change and do it all over again.

So basically that's a long winded... no you can't get away with stock alignment specs. The problem is that I don't know what should be used. I'm on a quest to find out.
 

Optigrab

Corporal
Sep 19, 2018
133
I do know when you corner and put a lateral load on the rear suspension you get toe in. This creates stability. I do not know what happens to toe when you accelerate. I can pretty much assure you it toes in as well as toe out would create instability. The problem is I don't know how much it toes in under acceleration (trying to figure that out).

The problem is you have to measure the toe change dynamically, that isn't easy. Then make a bushing to ball joint change and do it all over again.

So basically that's a long winded... no you can't get away with stock alignment specs. The problem is that I don't know what should be used. I'm on a quest to find out.
alot of that is over at 1addicts most of the people with this swap are autocross and track guys
 
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alot of that is over at 1addicts most of the people with this swap are autocross and track guys
Awesome! that sure would save a lot of time! So those guys have measured how the rear toe changes dynamically with the M3 parts? Could you send a link to where someone discusses that? It would be much appreciated.

Cheers,
Barry
 

Optigrab

Corporal
Sep 19, 2018
133
... no you can't get away with stock alignment specs. The problem is that I don't know what should be used. I'm on a quest to find out.
Dont know about deflection...you said you are looking for alignment specs that work that was what i was referring to. Tons of threads with people running m3 hardware discussing and testing alignment for various uses autocross track etc
 
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Dont know about deflection...you said you are looking for alignment specs that work that was what i was referring to. Tons of threads with people running m3 hardware discussing and testing alignment for various uses autocross track etc
Gotcha... @Silver_Sur4r_N54 was looking for alignment specs because he said he kept wearing out rear tires.

@Silver_Sur4r_N54 is it street driving that is wearing out the rear tires? How is the wear... across the whole tread or on the inside? Premature wear can mainly be a culprit of too much toe scrubbing the tire tread.

If you were to measure the rear toe change under bump with no load on the suspension (i've done this) you will get zero toe change. When you accelerate, the wheel will be pushed toward the front of the car and as the suspension squats (bump), there will now be a toe change, IE toe in. Assuming your car is stable under acceleration, what I suspect is happening is there is too much toe in as you accelerate. To solve this you would want to start with less "static" toe in on your alignment. This will result in less toe in under acceleration reducing tire wear. You will have to play around with this or maybe someone over at 1addicts, like @Optigrab suggested, has done it which will save you some time figuring it out.

Unfortunately I won't have a conclusion soon as I have another project getting in the way (grrr...). However I am looking to figure this out ASAP for developing e90 track suspensions. Hopefully in the coming weeks.
 
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Bnks334

Sergeant
Dec 1, 2016
271
New York
Awesome! that sure would save a lot of time! So those guys have measured how the rear toe changes dynamically with the M3 parts? Could you send a link to where someone discusses that? It would be much appreciated.

Cheers,
Barry
As you probably already know, this would require 3D modeling the suspension. Felix did measure the affect of static compression on the suspension (toe and camber deflection), but, I've found some of his numbers to be a bit odd. Some tests he has refined the data on, others, I don't think people really even understood any of what he did so the numbers go un-peer-reviewed lol. His data is spread out across multiple threads. Some of it is in the "ohlins" thread he made. Measuring changes dynamically, especially to see the affects of changing pickup points, is an entirely different ballgame.

I do enjoy reading your posts, and, I hope you continue to post up data. I've argued quiet a bit of what you're saying here and elsewhere with people like the "autocrossers." A lot of people just don't understand the affects of the suspension changes they are making.
 
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As you probably already know, this would require 3D modeling the suspension. Felix did measure the affect of static compression on the suspension (toe and camber deflection), but, I've found some of his numbers to be a bit odd. Some tests he has refined the data on, others, I don't think people really even understood any of what he did so the numbers go un-peer-reviewed lol. His data is spread out across multiple threads. Some of it is in the "ohlins" thread he made. Measuring changes dynamically, especially to see the affects of changing pickup points, is an entirely different ballgame.

I do enjoy reading your posts, and, I hope you continue to post up data. I've argued quiet a bit of what you're saying here and elsewhere with people like the "autocrossers." A lot of people just don't understand the affects of the suspension changes they are making.
Yeah 3D modeling the e9X suspension would be next to impossible. I've done it with the e46 and that was a pain and it is a much more simple suspension. For the e9X you would need some expensive equipment and a lot of time. The front has a virtual steering axes. The rear has a total of 10 pickup points PER SIDE not including the ARB, and then accounting for rubber deflection, and then figuring out what load to apply to deflect the rubber....... my head already hurts so I'll stop there.

BMW publishes the static toe change of the Non M e90 rear (also lateral and braking deflection). I posted the graphic earlier in this thread. About 10 years ago when the e90 first came out I measured static toe myself and got the same answer which is zero toe change. They don't unfortunately publish the M3 data.

Now i'm curious about the dynamic changes so I'm back at it. I will be using data acquisition with potentimeters and other measuring devices to figure out some basics. I don't like to slap parts on and test test test, it gets very expensive. I think the key here is to get a general understanding and apply principles.

Today I took a quick moment to look the the M3 front spindle vs Non m. In conjunction to a different pickup point on the Z axis of the tie rod (which changes bump steer), there is also a Y axis difference. What this means is the steering ackerman is also different on the M spindle.
 
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