[AtlasM]

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?

[ajsalida]

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.

[feuer]

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.

[AtlasM]

Originally Posted by ajsalida

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.

Well yeah, there's that too!

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.

[AtlasM]

Originally Posted by feuer

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.

Very interesting, at least someone else has had a similar thought to me. Here are a couple pics from your links:

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?

[ajsalida]

Originally Posted by AtlasM

Well yeah, there's that too!

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.

I think if you added longer stops you'd shorten travel, just bottom out sooner, and more often. Stock stops are not made to be in contact with something very often and would probably wear out quickly. Even without contact they can rot pretty fast.

[feuer]

Originally Posted by AtlasM

Very interesting, at least someone else has had a similar thought to me. Here are a couple pics from your links:

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?

[AtlasM]

Originally Posted by ajsalida

I think if you added longer stops you'd shorten travel, just bottom out sooner, and more often. Stock stops are not made to be in contact with something very often and would probably wear out quickly. Even without contact they can rot pretty fast.

It's not just the extra length, I'm mostly focused on how the xDrive and M3 bump stops have those rubber stoppers on them.

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.

[AtlasM]

Originally Posted by feuer

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?

Yeah, good point, so yeah, I'm thinking I need either the E9x xDrive or M3 bump stops. That rubber ring on the outside of the bump stop prevents it from compressing as much, right? In which case it would raise the effective spring rate of the bump stop.

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?

[ajsalida]

Originally Posted by AtlasM

It's not just the extra length, I'm mostly focused on how the xDrive and M3 bump stops have those rubber stoppers on them.

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.

If you're saying the stops are supposed to be engaged all the time and work with the shocks for extra damping that's simply not true. They are soft sure, but that's to provide a very progressive transition to bottoming out once engaged. They are made of a cheap foam that gets brittle and rots quickly and no way that is intended to take any kind of regular suspension loads.

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.

[feuer]

Originally Posted by AtlasM

Yeah, good point, so yeah, I'm thinking I need either the E9x xDrive or M3 bump stops. That rubber ring on the outside of the bump stop prevents it from compressing as much, right? In which case it would raise the effective spring rate of the bump stop.

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?

I honestly, ignored the bump stop hype on e90post and when I installed my Kony yellow with BMPS springs went with "regular" sport bump stops that the car had originally. I don't regret it at all as I know how lowered e9x feels and sound over potholes with shorter bump stops, too much boom and bam. So my advice to you is to either go with stock XI bump stops or e9x m3 as they are of similar design and height.

[AtlasM]

Originally Posted by ajsalida

If you're saying the stops are supposed to be engaged all the time and work with the shocks for extra damping that's simply not true. They are soft sure, but that's to provide a very progressive transition to bottoming out once engaged. They are made of a cheap foam that gets brittle and rots quickly and no way that is intended to take any kind of regular suspension loads.

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.

I don't mean that the car should be riding on the bump stops. I mean the bump stops are more involved with the normal operation of the suspension than simply stopping the shock at the end of its travel. Generally, under hard cornering, our cars are on the bump stops. Even the stock suspension acts this way. When the bump stop engages, it compresses, it doesn't fully stop the shock from moving.

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?

[AtlasM]

Originally Posted by feuer

I honestly, ignored the bump stop hype on e90post and when I installed my Kony yellow with BMPS springs went with "regular" sport bump stops that the car had originally. I don't regret it at all as I know how lowered e9x feels and sound over potholes with shorter bump stops, too much boom and bam. So my advice to you is to either go with stock XI bump stops or e9x m3 as they are of similar design and height.

Do you think the M3 with their flat bottoms are probably stiffer than the xDrive with the fingers?

[feuer]

Originally Posted by AtlasM

Do you think the M3 with their flat bottoms are probably stiffer than the xDrive with the fingers?

Is safe to assume that they are stiffer as these bump stops are designed to assist the springs and m3 springs have higher rate.

[feuer]

Originally Posted by AtlasM

I mean the bump stops are more involved with the normal operation of the suspension than simply stopping the shock at the end of its travel.

Originally Posted by AtlasM

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.

You answered yourself > these bump stop are not hockey packs to stop the shaft from bottoming out at the end of these travel. Although, in general longer travel is better achieving it thru shorter bump stops is not always the way to go as you have come to find out. Besides, these combinations of bump stops that are "advertised" on the forum are pretty much based on the bump stops height, whether they are shorter or taller, and not how stiff they are and the degree of what they will collapse/compress under load. That is the main reason why I just stick with the OEM sport on my 335i

[ajsalida]

Originally Posted by AtlasM

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?

No. Because for the situation you describe, the FSD's are basically behaving like a blown shock. You can't fix a blown shock with firmer or longer bump stops. You'll make it worse because a blown shock uses up travel quickly and bottoms out fast. Longer/firmer stop just means it will bottom sooner/harder.

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.

[ajsalida]

Originally Posted by feuer

You answered yourself > these bump stop are not hockey packs to stop the shaft from bottoming out at the end of these travel. Although, in general longer travel is better achieving it thru shorter bump stops is not always the way to go as you have come to find out. Besides, these combinations of bump stops that are "advertised" on the forum are pretty much based on the bump stops height, whether they are shorter or taller, and not how stiff they are and the degree of what they will collapse/compress under load. That is the main reason why I just stick with the OEM sport on my 335i

I think the reason people recommended e36 M3 stops, at least on XI cars, is they are much shorter than the OEM XI stops and cheap/easy to find. When you lower an XI with RWD-spec'd springs, it drops quite a bit more than non-XI, and far more than RWD sport. OEM RWD sport stops might work well on lowered XI, as I'm sure many others would. Furthermore sport stops on pro-kit RWD cars work also because pro-kit is not much of a drop from OEM sport.

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.

[feuer]

Originally Posted by ajsalida

I think the reason people recommended e36 M3 stops, at least on XI cars, is they are much shorter than the OEM XI stops and cheap/easy to find. When you lower an XI, it drops quite a bit more than non-XI, and far more than RWD sport. OEM RWD sport stops might work well on lowered XI, as I'm sure many others would. Furthermore sport stops on pro-kit RWD cars work also because pro-kit is not much of a drop from OEM sport.

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.

I completely understand why XI "drops" more (the strut body is mounted higher than due to CV clearance thus closer to the strut tower. I completely understand why shorter bump stop is needed. However the e36 m3 bump stops, like you said, are advertised solely because they are shorter and cheap/easy to find and not whether they are appropriately matched with e9x weight and spring spring rate.

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?

[AtlasM]

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.

[AtlasM]

Originally Posted by ajsalida

I think the reason people recommended e36 M3 stops, at least on XI cars, is they are much shorter than the OEM XI stops and cheap/easy to find. When you lower an XI with RWD-spec'd springs, it drops quite a bit more than non-XI, and far more than RWD sport. OEM RWD sport stops might work well on lowered XI, as I'm sure many others would. Furthermore sport stops on pro-kit RWD cars work also because pro-kit is not much of a drop from OEM sport.

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.

E36 M3 are 52 mm, E9x xDrive & M3 are 60 mm, E9x ZSP are 70mm. I don't think the ZSP bump stop on a lowered xDrive would be a good option.

[ajsalida]

Originally Posted by feuer

I completely understand why XI "drops" more (the strut body is mounted higher than due to CV clearance thus closer to the strut tower. I completely understand why shorter bump stop is needed. However the e36 m3 bump stops, like you said, are advertised solely because they are shorter and cheap/easy to find and not whether they are appropriately matched with e9x weight and spring spring rate.

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?

I thought the PS stops were SHORTER than ZSP??? BTW IIRC it was Steve Dinan who started the whole e36m3 bump stop thing, and included them on his first RWD e9x kits.

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

[ajsalida]

Originally Posted by AtlasM

E36 M3 are 52 mm, E9x xDrive & M3 are 60 mm, E9x ZSP are 70mm. I don't think the ZSP bump stop on a lowered xDrive would be a good option.

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.