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E36 M3 front bump stops don't work on a lowered xi with FSDs. Speedthane fixed it
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08-28-2016, 11:49 PM | #1 |
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E36 M3 front bump stops don't work on a lowered xi with FSDs. Speedthane fixed it
I have Koni FSD shocks and B&G S2 lowering springs on my E92 335xi. I chose them because the FSDs would keep my ride comfy and the B&G springs give a hair more lowering than the Eibach Pro-Kit with similar spring rates. I went with E36 M3 front (part # 31332225377) and Z4 M rear (part # 33507836826) bump stops.
Overall, I'm happy with the handling balance of this setup, but the front end doesn't do the greatest job coping with sharp bumps. It not-quite-fully bottoms out on bumps that it really should do a better job with. The rear is fine. I know the FSDs have a bit of a reputation for this behavior, but I've been thinking about ways to improve the situation, without having to ditch my practically brand new FSDs. So I started looking into bump stops. The conventional wisdom at least with the rwd cars is to do the E36 M3 front bump stops when lowering. From this post, I found a comparison pic of the E36 M3 vs E90 M Sport (part # 31336767333) front bump stops: The E36 M3 is noticeably shorter, at about 5.25 cm in length vs. 7 cm for the E90 M Sport. So for a rwd E90 where there's a fairly decent amount of front suspension travel, going with the E36 M3 bump stop of similar design but shorter length makes some sense. The E36 M3 bump stop looks almost exactly like a slightly longer version of what you'd end up with if you cut that first section off the E90 M Sport bump stop. So rather than cut down potentially worn-out E90 M Sport bump stops, you can get fresh new E36 M3 bump stops that are of similar dimensions. But what about the xDrive front suspension? It's totally different. Even in stock form it has a lot less travel than the rwd front suspension. The E90 xDrive front bump stop (part # 31336777636) looks like this: They have that rubber gasket or whatever it is, that's not present on the E90 M Sport or E36 M3 bump stop. I measured the ones that came off my car, and they're 6 cm in length. You know where I did find a bump stop with a similar rubber ring on it? The BMW Performance suspension. From this post I found this pic, the E90 M Sport front bump stop is on the left, and the BMW PS (part # 31338036012) is to its right. The BMW PS bump stops, in addition to having that ring like the xDrive bump stops, are also slightly longer than the E90 M Sport bump stops they are intended to improve upon. So here's my theory: maybe I should just be running stock xDrive front bump stops? These foam bump stops really act more like helper springs in that they still compress rather than act as a hard stop on the shock. Maybe the E36 M3 bump stops are too short and removing that rubber ring that's present on the xDrive and BMW PS bump stops is also exacerbating the problem of blowing through the FSD travel? Does this make sense to anyone else? Last edited by AtlasM; 09-15-2016 at 11:29 AM.. |
08-29-2016, 05:54 AM | #2 |
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Another explanation would be FSD's suck. The fact that they do not handle bumps and bottom out often (esp with lowering springs and XI) is well-documented. But people keep buying them.
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08-29-2016, 09:01 AM | #3 |
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I argued here about
http://www.e90post.com/forums/showth...1126622&page=2 e46 and e90 M3 bump stops have those rubber rings as well. BMWPS as well and like you said they are also longer than the "regular" sport bump stops but the BMWPS springs are shorter. The rubber ring adds to the bump stiffness thus adding to the total spring rate. Why BMW went will taller and stiffer bumps on e46 m3, e90 m3, e90 BMWPS and e90 XI ? All have shorter travel than "regular" BMW's. So how is that helping travel? Perhaps not with travel but helps with bottoming out and blowing up struts/shocks. |
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08-29-2016, 09:35 AM | #4 | |
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I knew there was definitely mixed feedback on the FSDs when I bought them, but my goal was to keep the ride as comfortable as possible so I rolled the dice. Sure, there's a thought in the back of my head that Bilstein B8s with their shortened bodies may handle bumps better, but for now I'd rather try to get the FSDs that I only bought a few months ago to work better. |
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08-29-2016, 09:44 AM | #5 | |
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E36 M3 vs E9x M3 (part # 31302283444) E46 M3 (part # 31332229778) The E46 M3 look pretty similar to the E36 M3 but with a limiter ring on them. The E9x M3 look very similar to the E9x xDrive. I couldn't find a picture with an exact measurement of them but since I know the E36 M3 are 5.25 cm and the E9x xDrive are 6 cm, and the E9x M3 is slightly longer than the E36 M3 in that top pic, it's probably similar in length to E9x xDrive. The main difference between the E9x xDrive and E9x M3 are the xDrive have these sort of "fingers" at the bottom tip of them that are not present on the M3. The E9x M3 is more of a continuous surface. This is just a theory here, but perhaps the E9x M3 bump stops with the continuous surface there are stiffer than the fingers on the xDrive? Which means maybe the best way to keep the front of the car from bottoming is to go with the E9x M3 bump stops? |
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08-29-2016, 09:49 AM | #6 | |
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08-29-2016, 10:43 AM | #7 |
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Is not me, don't bother with me, is BMW, Mercedes, Audi&VW, and Mazda, Koni's matched with Eibach lowering springs that in some instances could be sourced directly thru the car dealers all come with these "packer" add-on bump stops. Again, not me...I just follow the engineers, who I assume, scientifically discovered and decided to include those bump stops in the kit. In all seriousness: why would be the BMWPS bump stop be longer than the BMW Sport when the BMWPS springs are SHORTER than the SPORT springs?
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08-29-2016, 10:56 AM | #8 | |
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All these bump stops aren't really bump stops in the traditional sense. Bump stops are hard rubber things that catch the shock at the end of its travel, and generally not very big. BMW bump stops are squishy foam that are intended to compress, not be a hard stop. BMW calls them "additional shock absorbers," not bump stops. The bump stops are designed to be involved in the overall suspension stroke, not just at the very end of it. When the shock body touches the bump stop, it doesn't stop the shock body from moving. The shock, spring and bump stop all work together. So my thought is, the bump stop is the cheapest and easiest part of this puzzle to change out. |
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08-29-2016, 11:00 AM | #9 | |
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The E36 M3 bump stops are roughly 52 mm while the E9x xDrive and M3 are roughly 60 mm. But the E9x xDrive & M3 stops with the rubber rings are a firmer spring rate which I think will help prevent the shock bottoming as much. I'm also guessing the fingers on the bottom of the xDrive stop make that part of it less stiff than the M3. So here's a thought: on the rwd E9x, the BMW PS has stiffer bump stops than ZSP. Following that reasoning, the E9x M3 bump stop is similar to the E9x xDrive bump stop, so would it then make sense on an xDrive to upgrade to the M3 bump stop? |
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08-29-2016, 11:28 AM | #10 | |
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Look, the FSD's are known to be a gimmick, given that you're not even using them as recommended, and you're having problems that are also well known (weak blow off valves lead to lots of bottoming out). You're then adding something (longer stops) that will make it worse as a cheap "fix". What you need is more travel (taller springs) and/or better shocks. For example my XI car has Koni Yellows, e36 M3 stops, RWD eibach pro kit front springs. Hardly ever bottoms and roads out here are as bad as they can get (high mountains Colorado). My $0.02. |
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08-29-2016, 11:36 AM | #11 | |
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08-29-2016, 01:20 PM | #12 | |
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The E9x xDrive and M3 bump stops are only ~8 mm longer than the E36 M3 bump stops. But they have those rubber rings on them that make them stiffer. I believe the M3 stops with their flat bottoms are stiffer than the xDrive ones with the fingers on the bottom. Yes, the FSDs can blow through their travel more quickly than desirable. I'm not saying this isn't the case. I've experienced it. My original reasoning with choosing the E36 M3 bump stops was to still have a bump stop but give the FSDs as much travel to work with as possible. But that's resulting in bottoming. I'm trying to think of a way to reduce this behavior, without replacing the FSDs. In theory a stiffer, slightly longer bump stop will start compressing sooner and it will take more force to fully compress it, which I'm guessing could help stop the FSDs from blowing through their travel too quickly. At least that's my theory. You've got Koni Yellows, Eibach springs (which are pretty similar to my B&G springs), and the E36 M3 front bump stops. Don't you think it's possible that while the E36 M3 bump stop is a good match for the Yellows, given that the FSDs are much softer over sharp bumps than the Yellows, they might work better with a stiffer bump stop? |
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08-29-2016, 01:23 PM | #13 | |
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08-29-2016, 01:26 PM | #14 |
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08-29-2016, 01:37 PM | #15 | |
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08-29-2016, 02:47 PM | #16 | |
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People who insist these stops are part of the regular working suspension don't understand suspensions. Whereas they may be intended on stock shocks to engage sooner than you'd think, they definitely aren't supposed to do so a lot and certainly not at all on Konis or other aftermarket shocks. They are simply a very progressive foam stop to smooth out harshness when bottoming. Not designed to be crushed over and over on a regular basis as an integral part of a working suspension. The amount of force produced by these stops even compressed 1/2" is tiny. I understand what you're hoping to do, no harm to try it and see. I think if they are long enough and firm enough to actually provide any extra damping or spring rate vs the e36 M3 stops, they'll be engaging sooner when bottoming and be unbearable. And if they aren't they're not helping. But what you've found out is that the FSD's just aren't suitable and no amount of bump stop swapping will fix it. Quite a few people have found this out unfortunately. Last edited by ajsalida; 08-29-2016 at 03:00 PM.. |
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08-29-2016, 02:54 PM | #17 | |
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If you keep the stock XI stops and drop the car with eibach pro-kit type spring, you'd be riding around on crushed OEM stops and ride will be horrible. There is no magic to using E36M3 stops, they just happen to be much shorter and so more appropriate for dropped car. Last edited by ajsalida; 08-29-2016 at 03:16 PM.. |
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08-29-2016, 03:18 PM | #18 | |
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Perhaps, bump stop of same length by car with different weight and spring rate will be better match? Also, what is you take on BMW including taller bump stops with their Yellow springs that further lower the car that is on sport springs? |
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08-29-2016, 03:28 PM | #19 |
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Well, I'm going to do an experiment. I ordered the E9x M3 front bump stops. Once I have them on the car I'll test them out in the couple places I have the most trouble with bottoming. Not expecting a miracle, but hoping for an improvement.
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08-29-2016, 03:32 PM | #20 | |
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08-29-2016, 03:32 PM | #21 | |
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Again the key thing here is when you lower a car you want to maximize available bump travel, not restrict it. If the stops that were in place before lowering are now in contact, they are way too long. You want a decent amount of travel before the stop begins to engage (1/2" at least). The OEM BMW stops are all very soft and progressive, so at the beginning of engagement you don't feel a hard transition. However it firms up very fast (eg strongly progressive). The whole XI situation is so hard because once you lower it to where the goofy fender gap is mostly gone, you have very little travel left, since the lower shock body is placed higher than RWD to clear the axle. So the trick is to find a stop that is short enough to leave a decent amount of travel with no contact, but firm enough so that if you do bottom you don't destroy the shock. This is why coil overs with shorter shock bodies and cut down Koni yellows are popular, you get more travel. I think there are many OEM stops will do this more or less, but they won't change the fact that FSD's tend to bottom hard due to their design. Good read here: http://www.m3post.com/forums/showthread.php?t=427147 Last edited by ajsalida; 08-29-2016 at 03:52 PM.. |
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08-29-2016, 03:36 PM | #22 | |
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So wait now longer stops are bad? My point was many stops will work, depending on how low you've dropped the car. You want as much unimpeded bump travel as you can get for whatever height you've dropped. If you are bottoming out now with 52mm then going to 60mm is not going to help much. And no 70mm will not work well either. The problem is with the shocks not the bump stops. edit: Are you sure about those numbers? I don't think OEM ZSP is longer than OEM XI. I think the stops on my xdrive car were longer than 60mm. Last edited by ajsalida; 08-29-2016 at 03:43 PM.. |
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