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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > E36 M3 front bump stops don't work on a lowered xi with FSDs. Speedthane fixed it



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      09-12-2016, 10:35 PM   #45
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Had another opportunity to drive on some shit roads, which I feel like are increasingly plentiful around here.

Tonight there was one big bump on a little back road where there was a BUMP sign and I slightly underestimated how much of a BUMP it really was, and the front end still soaked it up great. My car is far from a rally car but it's kinda crazy how much of an improvement the Speedthane stops are over the E36 M3 ones.

Anyway, here are a couple pictures that show how tight the Speedthane stops fit on the Koni FSD strut shafts, and also how the dust boots are held on to the lower spring perches on the strut rather than the strut top mounts as is the case with stock.



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      09-13-2016, 11:34 AM   #46
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Quote:
Originally Posted by AtlasM View Post
Had another opportunity to drive on some shit roads, which I feel like are increasingly plentiful around here.

Tonight there was one big bump on a little back road where there was a BUMP sign and I slightly underestimated how much of a BUMP it really was, and the front end still soaked it up great. My car is far from a rally car but it's kinda crazy how much of an improvement the Speedthane stops are over the E36 M3 ones.

Anyway, here are a couple pictures that show how tight the Speedthane stops fit on the Koni FSD strut shafts, and also how the dust boots are held on to the lower spring perches on the strut rather than the strut top mounts as is the case with stock.



What is your assessment on body control with the FSD's? Do you detect any slight (or severe) bouncing of the front or rear suspension on rough roads? Or does the body stay relatively flat?
Do you ever encounter any float over dips, rises, and elevation changes?

Did your new Speedthanes affect any of these conditions?
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      09-13-2016, 12:32 PM   #47
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Quote:
Originally Posted by thakid22 View Post
What is your assessment on body control with the FSD's? Do you detect any slight (or severe) bouncing of the front or rear suspension on rough roads? Or does the body stay relatively flat?
Do you ever encounter any float over dips, rises, and elevation changes?

Did your new Speedthanes affect any of these conditions?
Overall I'd say the body control is solid. On slower-speed rough roads where there are lots of different smaller bumps and camber changes, the car is very planted.

The general behavior of the FSDs is to act like a firm shock but soften up in response to a high-frequency impact. Where this can cause problems is when you have a big high-frequency impact, or if you have a quick change in road surface angle, like when you're going down a hill and then at the bottom of the hill it's not just a regular dip, it's a change in road surface, i.e. two concrete slabs joining at an angle. Those two situations were giving the front of the car the most problems with the E36 M3 front bump stops. The problem was also sort of there going over a big rise with a quick dip after it where the suspension would go to full droop and then quickly compress.

The Speedthane bump stops made a big difference in all of these areas. Whereas before there just wasn't enough spring rate or compression damping to slow down the front end compressing, and the E36 M3 bump stops were too soft to do their jobs, the Speedthane stops are coming into play and stopping the front suspension from crashing through its travel. But because they're progressive, it's not hurting the ride. Based on this, I'd say that the principle on which the FSDs operate makes sense for balancing handling in turns vs. ride comfort, but they do need help from the bump stops when the shocks go soft and the suspension compresses a lot.

The rear with the Z4M stops doesn't have this problem to the extent that the front did with the E36 M3 stops, and really is pretty decent. I have Whiteline subframe bushings (not inserts) and Monroe rear upper & lower shock mounts. So for the most part the slop in the rear end is gone. But there's still a bit more compression happening in back over big bumps and road angle changes than maybe is ideal, so I'm thinking of doing the Speedthane stops in the rear as well. Basically the front of the car just feels a bit better than the back over big sharp impacts right now. The Z4 M bump stops I have back there are pretty close in overall size/shape to the regular E9x bump stops according to this threadm so they're probably not quite so soft as the E36 M3 front bump stops.



(E9x on left, Z4M on right)

The Z4M rear bump stops are 65 mm vs. 72 mm for E9x.





As for which Speedthane bump stops to put in back, I'm still trying to figure that out. Speedthane stops come in 58 mm & 76 mm. I have the 58 mm ones in front and those are just slightly shorter than the E9x xDrive fronts. 76 mm Speedthane stops would be taller than the E9x rear bump stops, 58 mm is shorter than even the Z4M ones. But the little bit of extra travel wouldn't necessarily be a bad thing.

Last edited by AtlasM; 09-13-2016 at 12:54 PM..
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      09-27-2017, 12:43 PM   #48
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Quote:
Originally Posted by AtlasM View Post
As for which Speedthane bump stops to put in back, I'm still trying to figure that out. Speedthane stops come in 58 mm & 76 mm. I have the 58 mm ones in front and those are just slightly shorter than the E9x xDrive fronts. 76 mm Speedthane stops would be taller than the E9x rear bump stops, 58 mm is shorter than even the Z4M ones. But the little bit of extra travel wouldn't necessarily be a bad thing.
Reviving this thread as I just started to research similar suspension changes and greatly appreciate all the research you did. Are you still happy with the Speedthane stops in the front? If so, are they - Speedthane 223539 Blue Bump Stop? Did you change the rear too?

Last edited by carlust33; 09-27-2017 at 05:11 PM..
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      09-27-2017, 07:11 PM   #49
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Quote:
Originally Posted by AtlasM View Post
I know the FSD shocks catch a bad rap on here because of their "pothole explosion" type behavior, but based on how they now handle bumps with these bump stops, I really think that the issue is not with the shocks themselves but that they've been paired with the wrong bump stops.

Yes, they do go soft in response to sharp bumps. That's what they're designed to do. But combine that behavior with a relatively heavy car with less suspension travel due to lowering springs, and while the E36 M3 bump stops are short enough to gain back some travel, they're way too soft to properly stop the shocks from bottoming out. The front of the car is now smooth and handles bumps great.

My goal when I chose the FSDs and B&G springs was to get the ride height exactly where I wanted it without resorting to coilovers, while also having a nice comfy ride, at least for a car running 19" summer tires and a performance suspension. With the Speedthane stops in front, that's now a reality.
I have a 2008 E90 w/E36 & Z4 bump stops (F&R) and Koni FSDs all around w/OEM sport springs (which aren't much different from Eibachs). The FSDs and E36/Z4 bump stops were installed about 3 1/2 yrs.

Have generally been happy w/the FSDs but I've had the same experience w/the E36 bump stops as you did. Was going to swap the front FSDs for adjustable Koni Yellows until I read this thread. May just swap the E36 front stops for Speedthanes instead to see if they have the same effect on my car as on yours.

You said that you bought the stiff blue Speedthane bump stops from RE Suspension. Are these the ones you bought?



See: https://resuspension.com/index.php/b...-40g-blue.html


They are not listed as Speedthanes but they look similar to the ones listed here on Summit Racing's website:

https://www.summitracing.com/parts/i...8-39/overview/

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Last edited by SSW; 09-27-2017 at 07:18 PM..
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      09-30-2017, 08:04 PM   #50
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You said that you bought the stiff blue Speedthane bump stops from RE Suspension. Are these the ones you bought?
FYI, I ordered these ones which based on reading other posts appear to be the ones: https://www.summitracing.com/parts/iss-310-3018-39
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      09-30-2017, 09:53 PM   #51
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Yes I bought my bump stops from RE Suspension. They were listed as part # RE-BR-COT58-40 on the order. When I search for that on their website (which has been changed since I ordered mine last year) it brings me here:

https://resuspension.com/index.php/b...-40g-blue.html

The Summit Racing link appears to be the same thing.

Honestly I'm not certain that these are absolutely the only solution, especially for less-aggressive springs. The main takeaway is, the E36 M3 front bump stops just are too soft for the weight of the E9x xi front suspension. Basically people choose the E36 M3 stops because they're an OE BMW stop that's shorter than the stock ones. But they're from a much lighter car, and way too soft. Yes being shorter is good but they are too weak to do their job on the much heavier xi.

The Speedthane stops worked for me because I have B&G springs which basically give you the most possible front drop on an xi. So I need some extra help. My car, being extra low in front, required more creativity with the Speedthane stops.

For springs that don't drop the front of the car as much as the B&G springs, it might be best to just go with the OE xi bump stops. I believe the stock xi bump stops are also better than the E36 M3 ones. You have the right stiffness for working with the weight of the xi. There's some room to lower the car before the stock bump stops get in the way. My car is lowered a lot.

The Speedthane stops require a lot of grease and effort to make them fit onto the strut pistons and you have to zip-tie the dust boots to the spring perches. Which is why for less aggressive springs, I think trying the stock xi stops is a better first move.

In the rear, I have Z4M bump stops which are very similar in shape and structure to the E9x ones but a little shorter. Unlike the E36 M3 front bump stops, these are a good substitute on lowered E9x cars, because you get a shorter stop but it's still the right shape and firmness. The part # is 33507836826. These fit just the same as the stock bump stops.

Last edited by AtlasM; 09-30-2017 at 10:03 PM..
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      10-02-2017, 12:04 AM   #52
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Ok, thanks for the advice, AtlasM.

I'm still using the OEM sport springs. The Eibach Pro Kits are supposed to similar to the OEM sport springs in terms of ride height and rigidity. Not sure how different they are than the B&G. The OEM sport springs offer a bit of a drop but not extreme.

Also not sure how the 335xi is different from the 335i. From what I've read, it's mainly a matter of height and the fact that the xi doesn't have a sport suspension. So, lowering the 335xi might just put it at the level of an 335ii w/the sport suspension which should mean the Speedthanes should work w/the FSDs on a 335i.

The distance between the front hub center and the lower edge of the front fender on my 335i is about 13.75." What's this measurement on your xi?

In any event, I'm actually leaning towards installing a pair of adjustable Koni yellows and an M3 strut brace (so that I can just remove the caps to readjust the shocks) instead. It's more expensive of course (about $1k for parts and labor) but it's a little "cooler" to look at.

Also with this set up it would probably make more sense to just go back to the OEM bump stops that were designed to be used w/the OEM sport springs and shocks in the 1st place. I kept the old parts when I installed the FSDs. I'm not sure exactly where they are now but it would probably be better to just buy new ones anyway. These stops can be found here: 335i E90 OEM sport spring bump stops.

Guess I'll just have to give it some more thought.
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      08-05-2018, 01:47 AM   #53
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Update from my post in Oct 2017:

Finally got around to doing what I said I was going to do above.

Just installed a pair of Koni yellow adjustable front struts w/OEM sport spring bump stops and an M3 brace tower in my 2008 335i. The FSDs w/Z4 bumpstops remain in the rear. Should also say that in the meantime, I installed M3 control arms and an E93 sway bar. Even so, switching to the Koni yellows and adding the M3 brace tower made a HUGE difference in handling.

After I picked up the car from the shop, I took it on a nearby 2 lane road where I routinely bottomed out in dips at speeds w/the FSDs in front. No more bottoming and the car tracked much better than it did before. The feels planted in the straights despite very uneven pavement and I can take it later into the turns at speed with control.

It now handles very much like my 2002 Toyota MR2 which is a much smaller, lighter and tractable car. VERY happy with the results of the change and recommend than anyone else who is unhappy w/FSDs upfront do the same.

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      04-11-2019, 10:55 AM   #54
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Quote:
Originally Posted by SSW View Post
I have a 2008 E90 w/E36 & Z4 bump stops (F&R) and Koni FSDs all around w/OEM sport springs (which aren't much different from Eibachs). The FSDs and E36/Z4 bump stops were installed about 3 1/2 yrs.

Have generally been happy w/the FSDs but I've had the same experience w/the E36 bump stops as you did. Was going to swap the front FSDs for adjustable Koni Yellows until I read this thread. May just swap the E36 front stops for Speedthanes instead to see if they have the same effect on my car as on yours.

You said that you bought the stiff blue Speedthane bump stops from RE Suspension. Are these the ones you bought?



See: https://resuspension.com/index.php/b...-40g-blue.html


They are not listed as Speedthanes but they look similar to the ones listed here on Summit Racing's website:

https://www.summitracing.com/parts/i...8-39/overview/

How do they fit and what are your thoughts on them?
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      04-11-2019, 11:40 AM   #55
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Quote:
Originally Posted by carlust33 View Post
FYI, I ordered these ones which based on reading other posts appear to be the ones: https://www.summitracing.com/parts/iss-310-3018-39
How do they fit?
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      02-16-2023, 07:26 PM   #56
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Have to give my opinion on this setup because it’s perfect.

Running Koni Special Active shocks with H&R Sport springs on my Xdrive E91 with Speedthane in the front and Z4M bump stops in the rear.

Crashing is gone, no more bottoming out even on the harshest roads.

Huge thumbs up. I don’t usually listen to what people have to say on forums but this worked great.
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      02-16-2023, 09:42 PM   #57
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Quote:
Originally Posted by doogee View Post
Have to give my opinion on this setup because it’s perfect.

Running Koni Special Active shocks with H&R Sport springs on my Xdrive E91 with Speedthane in the front and Z4M bump stops in the rear.

Crashing is gone, no more bottoming out even on the harshest roads.

Huge thumbs up. I don’t usually listen to what people have to say on forums but this worked great.
Have a picture of the drop those H&Rs gave you? I’m still debating on my future setup for my E91 xDrive as well.
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