Suspension Upgrade Options for the M3

[GOVCO]

Awesome information in this thread. I think, for my driving style, that I will be going the route of Dinan Stage 2. It may be a little on the higher end, but I feel it yields the best results for what I am looking for.

[Gee-klaw]

Originally Posted by JAJ

OK, so it's four months or so later and it's time for an update ...

You Sir, are a genius!

[dcgolfdr]

Originally Posted by GOVCO

Awesome information in this thread. I think, for my driving style, that I will be going the route of Dinan Stage 2. It may be a little on the higher end, but I feel it yields the best results for what I am looking for.

Get the camber plates installed at the same time to cut down on labor costs down the road!!

[GOVCO]

Originally Posted by dcgolfdr

Get the camber plates installed at the same time to cut down on labor costs down the road!!

You know, I thought of this very thing. Price difference isn't that much. Thanks for the heads up.

[1MOREMOD]

thanks for the write up good read.

[robbiedawg]

if you were looking for a ride that was no harsher than stock,but wanted a little less floatiness on high speed sweepers,what shock/struts would you guys go with?

[LateBraking]

Originally Posted by robbiedawg

if you were looking for a ride that was no harsher than stock,but wanted a little less floatiness on high speed sweepers,what shock/struts would you guys go with?

AFAIK there's not a shock only replacement, there's just spring replacements, coilover conversions for the stock shocks, and full coilover systems. What people would go with differs per person.

[robbiedawg]

what got me thinking about shocks only was this bilstein set from turner-
http://www.turnermotorsport.com/p-21...08-wo-edc.aspx

i just got the car,so i'm in the learning stage

[LateBraking]

Originally Posted by robbiedawg

what got me thinking about shocks only was this bilstein set from turner-
http://www.turnermotorsport.com/p-21...08-wo-edc.aspx

i just got the car,so i'm in the learning stage

Oh thats right, I had forgotten that RD Sport had Bilstein shock only replacements that they recommended with their springs. I would still go for a different setup like the Ground Control kit or KW V3's though.

[vincemca]

Great Information!http://www.m3post.com/forums/images/smilies/w00t.gif

[BigMacSmallFries]

Dude, I'm impressed. Thanks for putting this altogether, and for the others pitching in. Glad I have a working knowledge of our suspension set up.

So, what I'm gathering for those keeping their cars on the street and wanting to keep the costs low is that the Dinan springs with the shortened bump stops are the only way to go (from the lowering spring choices). Track use really requires stepping up to the Coilovers.

..I imagine for those of us tracking only a few times per year, the Dinan would be acceptable for the occasion. Any comments?

Originally Posted by JAJ

Essentially, I couldn't find a string of data points (in an hour or more of data) that would behave sensibly for more than a second or so. You're double integrating, so the process is to integrate from acceleration to velocity, detrend it, then integrate velocity to position and detrend it again. If you pick your start and end points when you can be confident that the suspension is at static height, then you can look at movements away from that static height. You can also look at motion from a "sensibility" perspective to see whether the data says the suspension is in places that physically it just can't go.

For sets longer than a second, you don't get consistent trends for detrending. The accelerometer signal has (what I presume is) low frequency noise components that make the integrated result wander around by 10's of cm over a few seconds.



I did a force vs velocity curve for the OEM dampers based on the acceleration data. F=MA, sprung and unsprung masses and known spring rates allow you to compute the forces and velocities of the suspension parts and graph the contribution from the dampers. This is actually easier to do because you only integrate once, and you can get enough samples to see the shape through the noise. It was an interesting exercise, but I can't find the data on my laptop, and I may have chucked it in a fit of cleaning up.

I thought a lot about analog accelerometers because I'm an analog circuits guy from decades ago. That would have been vastly easier for me to set up and calibrate than digital processing, but vastly harder to post process. I'd have been able to bandpass filter it, integrate and detrend it and get meaningful numbers without breaking a sweat. Digitally, it's not so easy for me. If I was starting now, though, I'd take a close look at Bosch BMA180 digital accelerometers - they have built-in bandpass filtering and data cleanup. They might work better.

[BigMacSmallFries]

In addition, I never have more than two people sitting in the car at any one time so my suspension never bottoms out. I tried driving over a speed bump at 70kmh once to see what would happen, it's the only time I've bottomed out. So I'm guessing since the rear seats and trunk are rarely used is that it's OK to have a smaller bump stop, with a spring that has a slightly higher spring rate.

Again... any insight or helpful comments?

Originally Posted by BigMacSmallFries

Dude, I'm impressed. Thanks for putting this altogether, and for the others pitching in. Glad I have a working knowledge of our suspension set up.

So, what I'm gathering for those keeping their cars on the street and wanting to keep the costs low is that the Dinan springs with the shortened bump stops are the only way to go (from the lowering spring choices). Track use really requires stepping up to the Coilovers.

..I imagine for those of us tracking only a few times per year, the Dinan would be acceptable for the occasion. Any comments?

[leo95se]

Originally Posted by JAJ

For those of you following this thread, ponder this:

Attachment 390235


The context is that I ran the car at a modest speed over a speed bump. As you can see, the wheel (red line) ran over it, the body (green line) followed with a time delay, and the suspension (blue line) ran out of travel twice on compression at about 3cm upward travel with a 5cm extension in between.

seeing this, i dont see how sleeve kits could benefit this/a car. We would be adding greater harmonics due to a higher spring rate coupled with stock (lower rate) dampers. it would seem to me, in a non-empirical approach, that this combo would create bounce. also, i dont know if the damper would be able to maintain the same comp/rebound as the spring, which could lead to larger issues.

any view on sleeve kits?

[adc]

Originally Posted by leo95se

seeing this, i dont see how sleeve kits could benefit this/a car. We would be adding greater harmonics due to a higher spring rate coupled with stock (lower rate) dampers. it would seem to me, in a non-empirical approach, that this combo would create bounce. also, i dont know if the damper would be able to maintain the same comp/rebound as the spring, which could lead to larger issues.

any view on sleeve kits?

Isn't the EDC damper adjustable? Even self-adjustable in certain modes?

[leo95se]

Originally Posted by adc

Isn't the EDC damper adjustable? Even self-adjustable in certain modes?

yes but the dampers are rated for 120(150?)lb springs. how can compression and bump compensate for a spring rate thats 400+lbs higher?

[adc]

Originally Posted by leo95se

yes but the dampers are rated for 120(150?)lb springs. how can compression and bump compensate for a spring rate thats 400+lbs higher?

I didn't think the KW sleeve-overs are 400lbs higher.

[M3SQRD]

Originally Posted by leo95se

yes but the dampers are rated for 120(150?)lb springs. how can compression and bump compensate for a spring rate thats 400+lbs higher?

I believe the effective spring rate, at least in compression, is much higher because the F suspension is setup to run on the bump stops. Also, the F suspension has been preloaded to ~200 lbf (may have an effect on stiffness if the spring rate is progressive).

From my early discussions with Jay at GC it sounds like the EDC (non-ZCP) dampers can handle a F spring with a 400-440 lbf/in rate, as long as the car is not lowered by more than ~0.5" and upper mounts with increased suspension travel are used.

[visvim_m3]

Awesome writeup, it all makes sense now why the BMW competition package only lowers the car by 10mm.