Suspension help. Rear end shimmy still.

Sep 19, 2018
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#61
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?
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.
Some info here

https://www.n54tech.com/forums/showthread.php?t=30461
 

[email protected]

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Jun 4, 2018
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#62
This is why I'm studying the rear suspension in detail. There just seems to be some not so accurate info out there. For example... Someone in that thread says the following which is not true: "Under braking for example the wheels will tend to toe out beyond zero"

I'll repost this from earlier, which is BMW documentation. Y axis is bump/rebound. So 1 is when the suspension compresses (bump), 2 is ride height, and 3 is when the suspension droops (rebound). The X axis is toe where towards the right (4) is toe in, IE positive toe. When braking the front compresses and the rear droops. So if you look at the green line (braking) you will see when the suspension droops (section 3) the rear toes IN. This is good as it creates stability.

bump curves.JPG


There is some other info in that thread about tire wear that I disagree with but its a moot point for this thread discussion.
 

Bnks334

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Dec 1, 2016
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#63
This is why I'm studying the rear suspension in detail. There just seems to be some not so accurate info out there. For example... Someone in that thread says the following which is not true: "Under braking for example the wheels will tend to toe out beyond zero"

I'll repost this from earlier, which is BMW documentation. Y axis is bump/rebound. So 1 is when the suspension compresses (bump), 2 is ride height, and 3 is when the suspension droops (rebound). The X axis is toe where towards the right (4) is toe in, IE positive toe. When braking the front compresses and the rear droops. So if you look at the green line (braking) you will see when the suspension droops (section 3) the rear toes IN. This is good as it creates stability.

View attachment 17835

There is some other info in that thread about tire wear that I disagree with but its a moot point for this thread discussion.
Is this a chart for the front or rear axel? Pretty sure this is from the "E90 suspension" BMW academy doc?
 

[email protected]

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Jun 4, 2018
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#64
Is this a chart for the front or rear axel? Pretty sure this is from the "E90 suspension" BMW academy doc?
Rear axle spring travel range. BMW participants manual E90 Suspension.
 
Sep 19, 2018
133
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#65
This is why I'm studying the rear suspension in detail. There just seems to be some not so accurate info out there. For example... Someone in that thread says the following which is not true: "Under braking for example the wheels will tend to toe out beyond zero"

I'll repost this from earlier, which is BMW documentation. Y axis is bump/rebound. So 1 is when the suspension compresses (bump), 2 is ride height, and 3 is when the suspension droops (rebound). The X axis is toe where towards the right (4) is toe in, IE positive toe. When braking the front compresses and the rear droops. So if you look at the green line (braking) you will see when the suspension droops (section 3) the rear toes IN. This is good as it creates stability.

View attachment 17835

There is some other info in that thread about tire wear that I disagree with but its a moot point for this thread discussion.
It would not surprise me if some of the people with issues had bent or damaged suspension components
either way the more info the better. Not sure if any of the time attack cars have posted their alignment info....
it would be interesting to see. Good luck!
 
Oct 28, 2017
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Monroe CT
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#66
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.
Yes I had 2 links don't know how I did that I'll fix when I get home im driving encase geico asks lol
 

Asbjorn

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Mar 10, 2018
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#67
You are welcome! I love suspension stuff. Anyone feel free to ask me anything suspension related!

Cheers,
Barry
Really enjoy reading about your findings. I am all bearings up front now, and had no idea I was changing toe behavior away from the intended design.

I would really love your inputs on how to adjust camber in this thread. At this point I am trying to figure out what the right direction is. Ie if I need less tire pressure or less camber to get towards a more even contact patch on track. Some of my track buddies run much more camber than me.
 
Jan 5, 2018
14
1
South Jersey
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#68
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.
apologies for not replying sooner but... I am wearing tires on the inside edge... I do not track with this car. It is all street driving... Spirited of course, a lot of hard launches and quick acceleration. But I believe you are right about the changes in Toe. When I had a e38 7 series that was lowered I would had the same problem with rear tires but replacing most of the rear suspension bushings helped tremendously. Thought possibly could be the same with the e92. But i think the Toe changes added with more power is just causing me to run the tires down faster.
 

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