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      03-10-2010, 01:20 AM   #1
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Arrow Why (Aggressive) Lowering Springs May Ruin Your M3, Part II

This is a continuation of this thread... http://www.m3post.com/forums/showthread.php?t=343880

Actual Bump Stop Test Data

By chance I was able to put an OE front bump stop into a force/displacement machine and measure its behavior, which is shown in red.

As I mentioned in the previous thread, the OE bump stop behaves progressively, meaning its stiffness increases with more compression. And when this bump stop compresses to about 1" in length (1.875" mark on the graph), its rate shoots up, adding significant stiffness to the total wheel rate. At this point the bump stop is almost like a hard piece of rubber in comparison to the rest of the system.

And the data shows just that...

So What Does This All Mean?

This means that in stock form, M3's front suspension has roughly 1.875"-2" of compression travel. In this range, compression force rises linearly, meaning the wheel stiffness is consistent (stiffness is slope of force/displacement graph). Consistent stiffness = predictable weight transfer = predictable/neutral handling.

Now, take a lowering spring that drops the front suspension more than 1". Because of the drop, the suspension now compresses from the right of the 1.0" orange line, and is only left with <~0.875" (aka very little) of linear, predictable compression travel.

Those with an aggressive drop will also easily run into the highly non-linear, unpredictable stiffness range of the suspension travel (right side of the second orange line). This of course leads to more unpredictable handling vs. OE. Moreover, because the front axle can now become very stiff at relatively short travel, more understeer will be experienced during cornering.

Next step is to get actual spring data.

This is meant to be an objective, fact-based discussion. Comments to my analysis are more than welcome.
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      03-10-2010, 01:37 AM   #2
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Okay, now I really want to meet you out a TWS just to show how predictable my car can be with it's unruly H&R springs
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      03-10-2010, 01:48 AM   #3
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Quote:
Originally Posted by JC919 View Post
Okay, now I really want to meet you out a TWS just to show how predictable my car can be with it's unruly H&R springs
You coming this weekend?
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      03-10-2010, 01:48 AM   #4
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don't you need to adjust a lowered car with aftermarket springs to have stiffer springs? thus the blue line is probably higher and steeper sloped to accommodate for the decreased travel? the graph would be right if someone simply cut their springs?
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      03-10-2010, 02:12 AM   #5
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My understanding is that it's pretty common for performance cars with OEM suspension to run at or close to the bump stops. It allows them to run softer springs while controlling car motions at the extreme/increasing perceived roll stiffness as your data shows. I'd guess the dampers are tuned to handle this. I think the 1" drop case is not the end of the world because you're still staying within the range of spring rate the dampers were designed to run at low frequencies (basic chassis motion) - though on a bumpy (normal) track you'd be at a disadvantage especially in the corners/braking/accelerating and additionally wear out your tires slightly faster.


The 1.8"+ drop with OEM geometry/travel/bump seems silly though....
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      03-10-2010, 11:19 AM   #6
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Quote:
Originally Posted by SCtud View Post
a lowered car with aftermarket springs to have stiffer springs? (...) the graph would be right if someone simply cut their springs?
+1, had the same question. Can't wait for the spring rate comparison to shed a little light...
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      03-10-2010, 11:22 AM   #7
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btw. i love the excel graph and orange line overlays i assume you work in finance?
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      03-10-2010, 03:06 PM   #8
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Starting from the OP of the original thread this is what I am basically getting. Please correct me if I am wrong.

If I own a car with EDC my safest and best bet for springs is either Dinan or Eibach. These are both minimal drops but provide the best ride(non bumpy) and the safest amount of drop for all other stock components. Now I am also understanding that people are changing other suspension components. Such as bumpstops and front guide supports.

Let me just give everyone a little background on my situation. I have not ordered my m3 YET. But EDC seems like a great option I always wanted. UNTIL I knew I was going to get aftermarket rims/brakes. Since day one of seeing/driving this m3 it always looked 4x4 to me.

My whole attitude on lowering a car is very negative. I know how many days of R&D went into developing spring/shocks/tire sizes/compounds/ spring rates etc etc. I always try and choose a suspension setup as close to stock as possible because I do not want to ruin one of the best parts of my new car especially an m3s suspension.

In tire and wheel choice I will not go larger then a 19` rim and probably end up with a lightweight 18`. I will not stretch the tire size much more then stock because I take into account all the actually development behind the antics.

But I cannot live with spending 9k+ on wheels/tires/brakes and having a gap I can fit 4 fingers in between my fender and my tire. I hope everyone understands my feelings and theory on the whole suspension thing. I always go with the theory function over form. So yes I LOVE the m3s handling and ride etc etc. If I can improve all of that while gaining somewhat of a drop that is my optimal route. I would not want a large drop for aesthetics only while loosing my ride to bumpiness and or rubbing.

Would it make sense for me to not even get edc and then just get coils. This is where I am at with this decision and I am actually happy because I didn't order the car yet SO I can weight my options. Thank you for the read and thank you to everyone who put technical data in this thread I learned a lot.
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      03-10-2010, 03:32 PM   #9
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i'm in a similar boat (though i already am stuck with EDC). i wonder if you plan on dropping the car just an inch (eibach or h&r), would you still do coilovers or would springs be good enough (whether you had EDC or not)?
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      03-10-2010, 06:14 PM   #10
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both threads present no evidence of "ruining" anything.

If you lower your car with just springs ... the springs will most likely be stiffer ..... therefore, you will wear the shocks out faster (EDC or not) since the shock will have to work faster.
You will also wear all the attached suspension components more .....and it is wise to check for cracks, worn bushings and loose nuts/bolts more often the with OE Springs.

The same applies to Coilover Kits minus the shock wear.

This BMW was obviously designed to use the bump stops as a helper spring ... and when you shorten the spring you increase the bump stops load .... is that 'ruin' your M3???

And please understand that you are not exempt from the laws of 'accelerated wear & tear' just because you have a full C/O kit and not just springs. The only thing you save is your OE Shocks.

Springs alone have never yielded better handling then a full C/O kit ..... only this is the 1st time its more popular ...to keep the EDC shocks.

Bottom-line: If you want better handling ... go with a rebutable Coilover Kit.
if you want to keep your EDC shocks and lower your car .. go with Springs.
Both will wear your suspension components faster and neither will 'RUIN' your M3.


And furthermore, for what it's worth ..... the same exact e90/e92m3 at the track ..... one with H&R Springs and one with OE Springs .... same driver, same hour ... The H&R spring'd M3 will lap slightly faster... and that's a fact.

Last edited by mastek; 03-10-2010 at 06:24 PM.
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      03-11-2010, 01:19 AM   #11
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Quote:
Originally Posted by rldzhao View Post
You coming this weekend?
Sorry bud, I was until I figured out this morning that I'm heading offshore. What's that MSR Houston date again? Hopefully it will be during one of my off weeks.
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      03-11-2010, 04:08 AM   #12
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Quote:
Originally Posted by mastek View Post
both threads present no evidence of "ruining" anything.

If you lower your car with just springs ... the springs will most likely be stiffer ..... therefore, you will wear the shocks out faster (EDC or not) since the shock will have to work faster.
You will also wear all the attached suspension components more .....and it is wise to check for cracks, worn bushings and loose nuts/bolts more often the with OE Springs.

The same applies to Coilover Kits minus the shock wear.

This BMW was obviously designed to use the bump stops as a helper spring ... and when you shorten the spring you increase the bump stops load .... is that 'ruin' your M3???

And please understand that you are not exempt from the laws of 'accelerated wear & tear' just because you have a full C/O kit and not just springs. The only thing you save is your OE Shocks.

Springs alone have never yielded better handling then a full C/O kit ..... only this is the 1st time its more popular ...to keep the EDC shocks.

Bottom-line: If you want better handling ... go with a rebutable Coilover Kit.
if you want to keep your EDC shocks and lower your car .. go with Springs.
Both will wear your suspension components faster and neither will 'RUIN' your M3.


And furthermore, for what it's worth ..... the same exact e90/e92m3 at the track ..... one with H&R Springs and one with OE Springs .... same driver, same hour ... The H&R spring'd M3 will lap slightly faster... and that's a fact.
Well said.
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      03-11-2010, 07:58 AM   #13
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My experience is consistent with what Richard said with just Eibach springs. I did not like the way my car behaved on track as it felt "nervous" when experiencing large compressions. Jay at GC attributed this trait to what Richard's chart shows above.

So by eliminating the stock bumpstop with either the Motons or the GC coilover conversion setup - the suspension behavior is more predictable and linear under track conditions. So now I have a nice street ride that I can easily adjust to current road conditions (i.e. press a button) that performs very well/predictably on track.

I'm not a suspension engineer or professional driver but my personal experience supports Richard's thesis/comments....

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      03-11-2010, 08:18 AM   #14
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I'm much happier with my Eibachs over the H&R's. The H&R's feel unsafe over 100mph while the Eibachs and OEM feel fine over 100+
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      03-11-2010, 09:43 AM   #15
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Quote:
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I'm much happier with my Eibachs over the H&R's. The H&R's feel unsafe over 100mph while the Eibachs and OEM feel fine over 100+
can you elaborate on what you mean by unsafe?

are you considering the GC setup or are you satisfied enough with the eibach to not mess with these? i guess i'm screwed since they don't seem to have a GC e93 setup.. oddly the e93 drops more with the eibachs, so i wonder if the slightly less drop on the eibach versus the h&r contributes to the extra ride comfort.
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      03-11-2010, 12:23 PM   #16
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Quote:
Originally Posted by SCtud View Post
don't you need to adjust a lowered car with aftermarket springs to have stiffer springs? thus the blue line is probably higher and steeper sloped to accommodate for the decreased travel? the graph would be right if someone simply cut their springs?
Yup, still a lot of variables missing to make a conclusion about absolute range of suspension travel with aftermarket springs. The increased spring rate of an aftermarket spring is one as well as the fact that most of the afterarket springs are progressive rate springs not linear like the OEM springs so that graph of the spring rate wouldn't be straight like it is shown.
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      03-11-2010, 08:39 PM   #17
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Quote:
Originally Posted by SCtud View Post
can you elaborate on what you mean by unsafe?

are you considering the GC setup or are you satisfied enough with the eibach to not mess with these? i guess i'm screwed since they don't seem to have a GC e93 setup.. oddly the e93 drops more with the eibachs, so i wonder if the slightly less drop on the eibach versus the h&r contributes to the extra ride comfort.
I'm not going with the GC setup as I am satisfied enough with my setup. When my shocks blow, that's when I'll be going coilovers but until then I am happy.


It feels unsafe only on roads that are not very smooth. When you hit a dip or a bump on the freeway at speeds I'd say even over 80 it definitely gives you the weird stomach feeling (oh shit feeling) with the H&R's, and you can feel something is off. Feels like the springs are too stiff and there is not enough travel for the shocks.

The Eibachs do not give this feeling. Sure you feel the road more than OEM but in no way does it ever feel "wrong" or mismatched.
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      03-11-2010, 10:28 PM   #18
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Thanks for all the feedback.

As I said in my OP, next step is to get actual spring measurements.

But my whole hypothesis is that at a certain level of compression, the stock bump stop will get so stiff that it doesn't matter what kind of aftermarket 'progressive' spring rate you have... When you use lowering springs that are too aggressive, your handling will become less linear and predictable, and you will get more understeer...

Stay tuned for more in the future.

Below is a video front a fellow member who had too an inappropriate bump stop set up in the rear axle...

Quote:
Get the bumpstop tuning right or this is what happens. Sudden and violent oversteer. I remember this day because I didn't think that bumpstops were the issue. I was on the phone with my shock guy and he had me decreasing the rear compression, which ultimately made it worse. Trimming the bumpstop .5" eventually solved the problem.
[u2b]<object width="480" height="385"><param name="movie" value="http://www.youtube.com/v/NjDNipRBMAI&hl=en_US&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/NjDNipRBMAI&hl=en_US&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="385"></embed></object>[/u2b]
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      03-13-2010, 05:38 PM   #19
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Great thread rldzhao, the M3 E36 bump stop is shorter. Would you be able to dyno that, so we can compare it's stiffness and behaviour to the E92 M3?
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      03-15-2010, 06:55 PM   #20
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why would you want springs anyways? the stock setup is amazing!
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      03-16-2010, 10:23 PM   #21
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Quote:
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why would you want springs anyways? the stock setup is amazing!
Say if you get a wheel/brake combo you want a smaller gap between fender and tire. IMO the m3 sits 4x4 compared to my 335i sport
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      03-17-2010, 09:06 AM   #22
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Quote:
Originally Posted by BaLLzZz View Post
Say if you get a wheel/brake combo you want a smaller gap between fender and tire. IMO the m3 sits 4x4 compared to my 335i sport
So if it's mostly for looks, some potential handling deterioration is of no consequence. Just go with what your heart desires...

Because stock appearance notwithstanding, the M3 handles so much better than a 335 sport...
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