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09-03-2010, 01:54 AM | #1 |
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Technical White Paper: Lowering Springs and Bump Stops, Take Three
After playing with various suspension set ups over the past two years (H&R, Dinan, Moton Street Sport, and soon Moton CS), I've learned quite a bit about this M3's suspension, and I thought it's time to write another article regarding the highly contentious topic of lowering springs and bump stops.
I will attempt to do this with no equations and pure common sense. Bump Stops Bump stops, as most of you know, are engineered elastomers. The main advantage of bump stops vs. a traditional spring is that the former can be engineered to provide variable stiffness at a very light weight. In the old days bump stops are simply installed to prevent the suspension from topping or bottoming out; they do not affect the suspension except at the limits of travel. However, modern day bump stops have started to play an increasingly more important role on street cars, especially on a every day sports car like the M3. Comfortable on the Street and Handles Well on the Track The E9x M3 has been praised by almost all car magazines in the world as the best all-around sports car on the market today... because you can comfortably take your kids to school and then pass everyone on the race track. The M3 is comfortable on the street because its springs are relatively soft, both the front and rear have wheel rates (lb/in) in the mid-hundreds. Having soft springs means that the wheels have greater travel with less abrupt transitions over bumps, which eliminates the rough ride experienced dedicated track cars. But softer springs are not usually well suited for the race track, because they allow too much suspension travel when the car is under high G forces, i.e. in a corner, or under braking, and this prolongs transitions and unsettle the platform. M3's Bump Stops The extensive use of bump stops is one reason why the M3, even with a very comfortable ride, can handle the race track so well. As Steve Dinan has pointed out, there is only about 0.5" of suspension travel before the front bump stops come into play; a similar situation applies for the rear. This is exactly the intention of the BMW engineers. These bump stops are engineered so that they are initially very soft (compressible by hands), but as compression increases, they get progressively harder. The bump stops gradually increase the effective wheel rate to control suspension travel and maintain the platform of the car. This is how the M3 gets away with soft springs. The "Cardinal Sin" of Riding on Bump Stops Bump stops have become a catch phrase for those who are considering lowering springs. Dinan has of course extensively used "modified bump stops" as the chief marketing slogan for why their kit is superior. But as I have explained above, even in stock form, the M3 is designed to ride on its bump stops more often than you think. Consider this, when there are four people in a car, your M3 will be already on its bump stops... and that is perfectly OK, as the bump stop is initially very soft. What is NOT OK
Remember, it is OK to ride on bump stops, but ride with good judgement. |
09-03-2010, 11:23 AM | #2 |
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Great write up. I have lowered my cars to far in the past for looks vs. function. I was leaning towards the Dinan stage 3 suspension kit. Which lowers things about 1/2".
I would be curious as to what you feel is the right range to lower without creating Track/Auto-X problems? Thanks, Shaun |
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09-03-2010, 12:02 PM | #3 |
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I went with the Eibach with E36 bumpstop route. Been really happy with the setup compared to the H&R with stock bumpstops.
Not sure how much the bumpstops have made a difference though, if any.
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09-03-2010, 12:04 PM | #4 |
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Don't lower the car at all. The effect on suspension geometry is much worse than the improvement due to reducing the center of gravity. This is usually compensated for with significantly stiffer springs.
If you lower for handling improvement you might have to do something like below. To improve the roll center, the strut is modified to lower the outer pivot point of the lower control arm. |
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09-03-2010, 02:02 PM | #5 |
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^Sure, excessive lowering will mess up the roll geometry. But a drop such as 0.5" is well within the stock suspension's normal operation conditions and will not have an adverse effect on the suspension performance.
The picture you are showing is probably a dedicated track/race car, judging from its front strut with remote reservoir (at least 2-way adjustable)... probably lowered 1.5-2" from stock? Any shots from the outside? |
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10-08-2010, 05:28 PM | #6 |
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Great topic. I've been thinking about bump stops a little also lately. I just recently purchased the Moton SS kit and I'm trying to figure out the best combination of bump stops, err or maybe at least a good starting point before I dive into the install. I think I have an idea in reading all the post from on the board but I figured I'd ask and maybe learn a little more.
I notice that the bump stops provided with the front Moton SS kit are roughly about 1" in total height. Significantly shorter than the stock front E92 M3 bump stops and E46. I assume from this and reading other experiences with the Moton SS kit that the bump stop provided for the front is wayyy to short and will allow the tire to run deep into the fender liner on heavy compression. That being said would it be recomended for the fronts to use something like the E46 or stock E92 bump stop with the Moton SS setup? I also noticed something new with rzm3's Moton Club Sport setup. The bump stops in those pics look quite a bit taller than the ones provided with the Moton SS kit pics. I guess in all this reading I've also been thinking about the shaved guide supports provided in the Dinan setup for the fronts. With the effort that goes into shaved guide supports, would it be more effective to select a bump stop of the correct height that would provide for the additional travel at the front shock but not too much that it allows the front tire to rub against the fender liner? Or is there something more the the shaved guide support provide that I'm missing. I would love to see a collection of specs for the different front bump stops that people have been using. I can measure up the ones that I have and post up if anyone is interested. As for the rears, I haven't even collected my thoughts on it but I'm thinking the options are maybe a little easier there?? Thanks, Royce M |
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10-10-2010, 12:25 PM | #7 | |
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So bottom line, would you suggest the Dinan Stg 3? I'm considering it and don't want to mess with the suspension if it's gonna negatively impact it's handling/ride/ etc. Thanks, |
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10-10-2010, 12:29 PM | #8 |
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Setup with H&R kit and E36 bump stops for about a year and a half now. Track the car monthly, no complaints here.
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10-11-2010, 05:49 AM | #10 |
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So again, my question is; will Dinan st3 improve or negatively impact the OEM handling, turning, stability, comfort, lateral G-forces, on the track, on the street?????????
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10-11-2010, 09:40 AM | #11 |
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Well, test drove the zcp at the track yesterday, (familiar track) and can confidently say the stg 3 felt smoother and more planted with better turn in than the comp pckg. Always fun to drive on track, but really wanted MY car on the track after about 2 laps. Really made me appreciate my car
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10-11-2010, 01:08 PM | #12 | |
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Klammer, So you've had the opportunity to make a direct comparison of the ZCP and your M3 with the Dinan stage 3? And you feel that your M3 handles better? Can you give some more specifics? I wonder though if that is because your used to driving your M, then you jump into someone elses and it's probebly gonna feel a bit different I would think. Just a guess though, I got a buddy that just took deliver of a '11 M3 with the ZCP. Haven't had a chance to drive it though. Thanks, |
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10-11-2010, 01:38 PM | #13 |
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the good thing is it was on a track that i have driven on now 5 times this year so have a fairly good idea of what i can and cant do on that track. my car just seems to track better, holds the line tighter and faster than the zcp. I put all the settings as i run them on my car, so that isnt a variable not adjusted for. also, felt less body roll on some of the faster corners and just felt i was able feel where my front end was more on my car and thus push it more. Just feels like a tighter, better handling ride... am really enjoying this car
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10-11-2010, 11:00 PM | #15 | |
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I did try stage 1, which pretty much handled like stock. Stage 2 will help also, especially on the track, as it gives more negative camber and keeps tires happy in corners. |
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10-12-2010, 12:31 AM | #16 |
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Yeah, I'm wondering if the improvement felt Stage III vs. ZCP is due to the entire Stage III package or the negative camber the Stage III kit dials in (comes with camber plates plus the drop, probably gives about -2.0 up front I'd guess). Less body roll aside (bars), the increased negative camber would certainly make a difference. In any case, that's a pretty hearty endorsement for the Stage III kit vs. stock ZCP!
On non-ZCP cars, w/o lowering or camber plates IIRC front camber maxes out at a bit over -1.0. What's the ZCP stock alignment like? I'm betting it's no where near as aggressive as the Stage III kit offers. Klammer, I'm not discounting your impressions at all. I'm just wondering if the camber is giving you better turn-in and a bit more confidence given your driving style. An additional degree of camber makes a big difference, especially on the track or in canyon carving. From the reviews I've seen the Dinan Stage II and III, I don't think you can go wrong that direction IMO. Lots of happy folks with these set ups, and it's a much cheaper option than an '11 with ZCP. Last edited by Finnegan; 10-12-2010 at 12:38 AM.. |
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10-12-2010, 01:57 PM | #18 |
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Depends on how you drive (and where--track, autox, street, canyon carving, mixed use, etc.) and how much negative camber we're talking about. Stock alignment maxes out at -1.0 IIRC; another half to one to even 2 degrees may not be "excessive" as the answer is "it depends". Run in an autox will stock camber and you'll eat the outside of your tires very quickly....run an autox appropriate camber on the street and you'll eat the inside of your tires.
The other thing to consider is toe. Toe is often more of an issue in tire wear than camber when camber is a more moderate levels (e.g. aggressive street). Combine toe with camber and tires can disappear quickly. A lot of guys who run a lot of camber tend to run close to zero toe in (or a very slight amount of toe in). Like anything suspension and tire related, it all gets very complicated very quickly. There's balance between front and rear alignment settings to consider... The type of tire you run has an impact on camber selection, tire pressure makes a difference, driving style makes a difference, and the car and it's suspension geometry, weight balance, etc. play in as well. Skill and ability (understeer at limit vs. neutral vs. oversteer) as a driver play in too. Weather conditions (snow, rain) play into decision making as well. Stock settings and OEM recommended tires are generally designed for a good compromise between tire life, performance, and safety. These settings will not, however, satisfy more performance oriented drivers--hence things like camber plates, wider wheels/tires, coilovers, etc, and some experimentation and adjusting. Probably as general rule if you spend a lot of time on the freeway or long distance straight driving you probably want less negative camber; if you drive aggressively on the curves then you probabably want more negative camber. And it pays to keep an eye on tire wear so you can address any uneven wear issues before the tires are gone.... I'd run some searches and see what folks have found works best for various applications and situations. There really is no one "right" answer.... Last edited by Finnegan; 10-12-2010 at 02:05 PM.. |
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10-12-2010, 08:59 PM | #19 |
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Finnegan summarizes it very well.
For a primary street car that sees a few track days a year, simply remove your guide support pins and max out the camber. You can get about -1.4 deg front if not lowered. For a primary track car with some street duty, you can go in the low-mid -2's. For a race car probably around -3. My rear camber has always been very similar to my fronts, perhaps slightly more positive. For the E9x M3 it seems that it does not need as much static camber as the E46's... probably due to a more aggressive dynamic camber curve. |
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03-07-2011, 03:40 PM | #20 |
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So based on your experience and the different setups you have had, what setup would you recommend if I don't want to "spring" for the Dinan Stage 1? I have a 2009 M3 E90 with EDC. I guess what I'm asking is which gets closest to the Dinan setup without the cost.
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03-08-2011, 11:28 PM | #22 |
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I have a 2011 ZCP. I want to put 20's on the car. Yes, mainly for aesthetics.
I don't think they'll look right at stock height and I just want to drop the car a tad more. It seems that the eibachs will drop the comp package a bit more and I'd be in good shape aesthetically. However, I don't want my car to bouncy as others have reported... I've heard the H&R are too stiff.... but I'd rather have stiffer than bouncy.... I have heard that the dinan won't lower a ZCP car much if any. Just so ya know. I have read all the sussy threads and done tons of research and I still have no idea what to do. I really need some good advice. I don't want to go cheap with springs if a coilover will give me better ride quality. (DD, street use is more important to me and I'd like a little better performance) I will consider paying for something nicer, I might even drop some money on the Moton street sport...but this car won't see the track much. As I said, I want to lower my car just a bit more to make the wheels look better and I want to maintain my ride quality. What would YOU do? Would you go Eibachs? Would you go Moton SS? Would you go with something like a simpler coil over setup from Ground Control or AST? A lot of my buddies say that the KV3's are a cheap solution... I'm so lost. Please help. |
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