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Suspension & Braking Forum by BimmerWorld
Have some questions about suspension or brake setups for your E46 BMW? Get all your answers here!
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Old 04-03-2007, 08:17 PM   #21
Nico3k
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It's great threads like this that keep me from ditching this forum

Mr Paddle.Shift: that was an excellent explanation! They should force people to read your posts before they can register!
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Old 05-21-2008, 02:45 PM   #22
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Great thread regarding the functions of a swaybar. We need more of this types of threads.
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Old 05-31-2009, 11:47 PM   #23
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I read like half of the first page so far cause theres a **** load of reading. Anyway when i take medium fast turns my car reachs its max then the back kicks out and then its like the whole car starts sliding to the outside. I wanna say it understeers but its not like the understeer i know. Same thing though.

And thats with DSC completely off. That might have been because of my shitty continetals. Ive got dunlop direzza going on tomorrow. so ill let you guys no whats up then. But i think i need a rear bar on the stiffer side and a medium front

Is that correct?

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It's great threads like this that keep me from ditching this forum

Mr Paddle.Shift: that was an excellent explanation! They should force people to read your posts before they can register!
Whatd you get for the ticket in your sig?
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Old 05-31-2009, 11:48 PM   #24
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Old 10-24-2009, 06:18 PM   #25
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To continue the link-fest for those interested - here is a great overview of suspension components and vehicle dynamics (plus a nice discussion on tires) - "Design and optimization of Suspension Systems and Components"
http://129.241.63.76/prodsim/Hjulopp...tReport_v1.pdf
Is there an updated link for this report?
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Old 10-24-2009, 06:37 PM   #26
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Is there an updated link for this report?
I can't find one, but PM me your email address and I'll send it to you (2MB file)

You also might enjoy this - The Automotive Chassis: Engineering Principles
http://www.scribd.com/doc/15362943/T...-Stoll-Betzler
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Old 09-07-2012, 02:22 PM   #27
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I finally registered here so I can actually use some of the info I have recently learned. I studied vehicle dynamics in school. Duke W and MrPaddleShift have made great points so far. Something no one has seemed to mention is roll steer and chamber change as a result of roll.

First, roll steer. Simply put, when your car leans into a turn (rolls) the suspension geometry changes. Sometimes the kinematics work out so that the inside or outside tire or both may turn a bit adding or subtracting steering angle from the wheels. Most setups try to minimize the roll steer, but if you have any rolls steer I think you would want positive. That is having the wheels add steering angle into the turn under roll. So, if your suspension exhibits roll steer, then a softer anti-sway bar will allow more roll and thus more steer, which makes the car feel less understeer at the steering wheel (notice I say at the wheel, the tire will still be understeering, but is automatically adding steering angle that you can't feel). For a stiffer roll bar the roll steer could be lessened thus seemingly added understeer (at the steering wheel).

Second, camber angle is important. Radial tires are affected less by camber angle than biasply so this effect may be negligible. In a turn the tires also tend to lean in or out, adding or subracting camber (more body roll will create a larger effect, not a linear relationship on most any suspension). In a turn the inside tire will lean in and the outer tire will lean out. This lean creates lateral force in addition to the slip angle of the tire. If you turn your wheels to the limit while stationary and get out, you will see that the tires are leaning. BMW has designed the suspension geometry so that under high lateral acceleration, the tire will still lay flat on the road. The body roll tilts the tire a few degrees the opposite way and it is standing straight up again. By increasing the siffness of the front roll bar you decrease the effect of BMWs steering geometry and remove the lateral force added by the camber change. This will induce understeer.

These are not the largest factors, but just two I saw weren't mentioned. Suspensions are so complex that to tell anything you really have to just test in the real world and at minimum have a full kinematic model of the system. Some of this may be unclear. If it is just ask and I'll try to elaborate.

For those interested, I use Gillespie "Fundamentals of Vehicle Dynamics" for my everyday references. You can find a copy online somewhere for free if you really want one, but I think linking to it would be a violation of rules here. And yes I know this thread is old as balls, but thought I'd add to the forums already huge knowledge base.

Last edited by WDE46; 09-07-2012 at 02:25 PM.
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Old 09-07-2012, 02:25 PM   #28
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This thread is so old, it's safe to say most of the users who posted on the first page have now passed away.
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Old 09-07-2012, 03:31 PM   #29
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This thread is so old, it's safe to say most of the users who posted on the first page have now passed away.
Not true. More information is always better and new owner need something to reference.
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Old 09-07-2012, 03:36 PM   #30
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Not true. More information is always better and new owner need something to reference.
What do you mean not true?
Original posters could have died since then.
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Old 09-07-2012, 05:01 PM   #31
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More information is always better
I disagree. Too much information is most certainly a bad thing, especially when it inundates an individual to the point of not being able to make a sound decision. Also, it doesn't help when a lot of 'info' is merely speculation.
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Old 09-07-2012, 06:44 PM   #32
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This thread is so old, it's safe to say most of the users who posted on the first page have now passed away.
really, these are people that have a lifespan longer than a fly

actually the first four posters have "last activity" 8-31-12, 8-30-12, Today, and Today. i think it's safe to say "most of the users who posted on first page" have not passed away.

all in all a good thread/read
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