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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > So I cut my bumpstops today...



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      05-04-2013, 01:43 PM   #1
thecadman99
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So I cut my bumpstops today...

After a lot of worrying about it, looking at the ridiculous prices for new, smaller bumpstops, and after getting tired of my "bumpy" ride, I decided to take out my rear bumpstops and cut them.

I should add that I am running Eibach pro-kit springs that have a bit of a drop, along with BMW performance suspension. Its very stiff and always soaks up the small stuff fine, but larger stuff is too stiff for this old guy. Could it be the long bumpstops are contacting too soon?

Here are my factory bumpstops as removed today:


I didn't really want to cut them as the taper and the inside (with the slight hollow area as shown) is designed to progressively start adding the bump resistance.
Still stock here, but you can see the undercut inside the hole.


So I bit the bullet, cut off the tip, and cut a taper with my trusty swiss army.


It looked pretty rough, so I got out my rotary tool, and a barrel sander, then a round bit to smooth out the taper, and add the undercut back into the bumpstop:


Here they are, ready to go, not perfect but hopefully workable. They both popped right back into the shock sleeve without problems.
I used this opportunity to coat all my rubber shock hardware (including the stops) with protectant.


Now, you probably want to know if it improved the ride? Um, I dunno yet! I'm heading out with the missus to watch Iron Man 3 so I'll post how it rides on the way back.

I didn't have any spring compressors so I couldn't do the front but I fully plan on doing the same thing as soon as I can borrow the compressor from my friend.

UPDATE: After test driving it was obvious that cutting the stops made a big difference. At first I was a little worried, going around the first curve I could feel the rear was "looser" not bad but it definately had some wiggle that wasn't there before. After a couple of miles through some of the worst road undulations, and transitions I was very happy with the way the rear was soaking up bumps and NOT bouncing (and so was the missus!).

To think I was ready to throw money at this problem when the bumpstops were the main cause of my overly firm suspension.

I took a speed bump straight on, and my wife even noticed the difference between the front and rear and how the rear soaked up the bump with minimal drama. I am super happy with the results of such a small adjustment.
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Last edited by thecadman99; 05-04-2013 at 08:17 PM. Reason: Updating info
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      05-05-2013, 09:47 AM   #2
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Good job on this. I hate when I see people arbitrarily cutting nubs off the bump stops which causes a drastic loss of progression that is needed for a stop to act properly.
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      05-05-2013, 02:30 PM   #3
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Quote:
Originally Posted by thecadman99 View Post
After a lot of worrying about it, looking at the ridiculous prices for new, smaller bumpstops, and after getting tired of my "bumpy" ride, I decided to take out my rear bumpstops and cut them.

So how's she ride now?

Had that issue - handling fairly flat but mondo bumpy. Increased ride height to ~0.5" below stock, right for my setup - more roll, but c-o-m-f-y. Still goes around a corner.
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      05-05-2013, 02:40 PM   #4
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So how's she ride now?

Had that issue - handling fairly flat but mondo bumpy. Increased ride height to ~0.5" below stock, right for my setup - more roll, but c-o-m-f-y. Still goes around a corner.
Still riding great! Ordering e36 m3 front stops to put in this week.
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      05-05-2013, 10:11 PM   #5
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I cringe a bit every time I see someone cutting and modifying their bump stops:

They are designed to work like a spring with a progressive spring rate. If you cut the top portion of the bump stop, you are essentially changing the effective "spring rate" of the bump stop. So you loose a lot of the comfort because the softer portion of the bump stop is now gone.

This becomes an even bigger problem for a lowered car because you are now risking the possibility of the shaft of the shock travelling further than designed and therefore damaging the shock valves or even bending it.

Finally, when you hit the bump stops, you have exhausted all the suspension travel and at this point and your car handles like crap.

My advise to you is to avoid lowering the car to the point where you are hitting the bump stops. All kinds of bad stuff happens when you get to that level...

EDIT: If you were hitting the bump stops previously, then your springs are too soft, your car is too low or both.
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      05-05-2013, 10:15 PM   #6
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      05-06-2013, 05:34 AM   #7
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Vasillalov, you do realize that the factory suspension rides the bumps at every single bump, right? There is about .25" of free stroke on the damper before engaging the stops. BMW uses them as supplemental springs.
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      05-06-2013, 06:54 AM   #8
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Quote:
Originally Posted by subieworx View Post
Vasillalov, you do realize that the factory suspension rides the bumps at every single bump, right? There is about .25" of free stroke on the damper before engaging the stops. BMW uses them as supplemental springs.
I agree.
I know cutting them isn't the best but I honestly don't think anyone can lower an e90 without changing or modifying the bumps (without coilovers or modified perches).

Mine were obviously riding on the stops and that is with the relatively small drop of the Eibach springs.

I already ordered a set of e36 m3 stops for the front and I'll be replacing the cut ones above with the Z4 or e46 m3 bumps, whatever works better when I get them in.

They are definately designed to engage early. BMW's performance suspension chart even lists them as "auxiliary shock absorber"
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      05-06-2013, 07:06 AM   #9
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Quote:
Originally Posted by subieworx View Post
Vasillalov, you do realize that the factory suspension rides the bumps at every single bump, right? There is about .25" of free stroke on the damper before engaging the stops. BMW uses them as supplemental springs.
That's exactly my point here.

1. You just changed the effective spring rate of the suspension making it way stiffer
2. You are now allowing for the shock shaft to travel more than intended which *could* potentially damage the shocks internals and even bend them

Honestly, I do not think that our cars should be lowered too much. Also, a properly designed suspension kit will include new bump stops.
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      05-06-2013, 07:54 AM   #10
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Also have Eibach pro kit (xi) and cut 1" off the rear bumps from the non-progressive end. Still fits into the dust boot. I was a little worried that too much of the stiff part was being thrown away but so far so good, one winter and some pretty rough roads out here. Fronts I used e36 m3, uncut.

Funny on my e36 m3 which also has koni/eibach you have to cut off the stock OEM bumpstops. For that I got new ones and trimmed them off non progressive end as well.

OP, Would be interest to see a pic if you have the chance, comparing the Z4 rear stops to your trimmed ones. Thx.
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      05-06-2013, 12:49 PM   #11
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Also have Eibach pro kit (xi) and cut 1" off the rear bumps from the non-progressive end. Still fits into the dust boot. I was a little worried that too much of the stiff part was being thrown away but so far so good, one winter and some pretty rough roads out here. Fronts I used e36 m3, uncut.

Funny on my e36 m3 which also has koni/eibach you have to cut off the stock OEM bumpstops. For that I got new ones and trimmed them off non progressive end as well.

OP, Would be interest to see a pic if you have the chance, comparing the Z4 rear stops to your trimmed ones. Thx.
I'll get a side by side. I should have- stock e90 rears, stock e36 m3 fronts, stock e46 m3 fronts, stock z4 rears, cut e90 rears.

I wonder much variance manufacturers have with the density of the foam they use... I have a feeling most just copy the shape of the original and use the same density for them all.
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      05-06-2013, 03:46 PM   #12
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      05-06-2013, 04:35 PM   #13
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Also have Eibach pro kit (xi) and cut 1" off the rear bumps from the non-progressive end. Still fits into the dust boot. I was a little worried that too much of the stiff part was being thrown away but so far so good, one winter and some pretty rough roads out here. Fronts I used e36 m3, uncut.

Funny on my e36 m3 which also has koni/eibach you have to cut off the stock OEM bumpstops. For that I got new ones and trimmed them off non progressive end as well.

OP, Would be interest to see a pic if you have the chance, comparing the Z4 rear stops to your trimmed ones. Thx.
Found some comparison pics in this thread:
http://www.e90post.com/forums/showthread.php?t=699650
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      05-06-2013, 04:35 PM   #14
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Quote:
Originally Posted by thecadman99 View Post
I'll get a side by side. I should have- stock e90 rears, stock e36 m3 fronts, stock e46 m3 fronts, stock z4 rears, cut e90 rears.

I wonder much variance manufacturers have with the density of the foam they use... I have a feeling most just copy the shape of the original and use the same density for them all.
Cool, thanks. BTW for racing purposes just abut any spring rate/foam density bump stop can be purchased, many shapes too. Like these guys

"Our force ramps perfectly linearly, even better than the BMW!" LOL

http://fatcatmotorsports.com/FCMstops_comp.htm

For the street this is probably not so big a deal.
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      05-06-2013, 04:40 PM   #15
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Found some comparison pics in this thread:
http://www.e90post.com/forums/showthread.php?t=699650
Ooo nice find. That Z4 rear does not look much shorter than the OEM, but the front e36 M3 is the perfect length for lowered car.
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      05-12-2013, 08:17 PM   #16
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So an update- I got a box of bumpstops in and worked on my fronts today.
I needed bumps for my e36, so I got a few different ones to experiment with.
Left to right- e36 m3 front, e46 m3 front, e90 (non sport=huge!) rear

Note: Might want to tell the wife what's in the box before you whip out one of those non-sport bumpstops....









Heres the factory e90 sport front bump beside the e36-


Really wanted to use the e46 front bump because it was a little stiffer than the e36, but the bellows didn't fit as well. Probably would have been fine, but I ended up going with the e36 bump.



Passenger suspension mount was seized!- POP THE CAP IN YOURS AND GREASE THEM. Its easy- Pop the hood, pry off the caps and add some lube-



PB Blaster, detail brush, brake cleaner, spin, clean, brush, spin clean...
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E36 Bump in bellows


Cleaned all the rubber mounts, they still looked good:


No need to remove the strut, just tilt it over for replacing bumps (or springs)


Mounted at full droop


Here is how I pre-tensioned the strut before tightening down the control arms. Just let the jack down slowly with a block under the control arm. When the car stops moving down, and the weight is on the block, tighten the release on the jack. Always have a a jack stand! (yes I know its in a bad spot!)


The control arms must be torqued correctly! 50lbs plus 90 degrees. There is a great vide on youtube.


The change in ride was not nearly as drastic as when I cut the rears. I did notice that bridge transitions and other sudden jolts were less jarring than they were before.
"Somewhat spirited" driving felt exactly the same as with the larger front stops. I didn't get a chance to try the stops close the the limit- the wife doesn't care for anything over .5g....

I'm going to do my e36 next- probably cut the long rear stops to a suitable level and use the other m3 fronts.
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      05-13-2013, 10:51 PM   #17
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I'll get a side by side. I should have- stock e90 rears, stock e36 m3 fronts, stock e46 m3 fronts, stock z4 rears, cut e90 rears.

I wonder much variance manufacturers have with the density of the foam they use... I have a feeling most just copy the shape of the original and use the same density for them all.
Great write up. Did you end up installing the Z4 bumpstops? If so did it make much of a difference? Trying to resolve a "jittery" rear end issue after upgrading to Konis/Eibach Pro. Thx!
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      05-14-2013, 06:38 AM   #18
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Great write up. Did you end up installing the Z4 bumpstops? If so did it make much of a difference? Trying to resolve a "jittery" rear end issue after upgrading to Konis/Eibach Pro. Thx!
No, after looking at the Z4 bumps, were so similar to my cut ones that I didn't bother with the change.

If you look at the pic of the long non-sport rear bumpstop above, its pretty much the same as the sport, minus one segment- the Non-sport has 4 segments, the sport has 3, and the one I cut shortens it down to two.

If you didn't want to fool with cutting the factory bump, then I think you'd still see a great improvement with the Z4.
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      05-14-2013, 08:08 AM   #19
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No, after looking at the Z4 bumps, were so similar to my cut ones that I didn't bother with the change.

If you look at the pic of the long non-sport rear bumpstop above, its pretty much the same as the sport, minus one segment- the Non-sport has 4 segments, the sport has 3, and the one I cut shortens it down to two.

If you didn't want to fool with cutting the factory bump, then I think you'd still see a great improvement with the Z4.
Thanks. I have a M Sport version but xDrive, therefore my suspension is non-sport (Thanks to the brilliant product line managers/decision makers @ BMW... ). I did have the bump stops cut as part of the Eibach install, but may put in Z4 ones anyways the next time the rear suspension is removed. Thanks again for the feedback.
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      05-16-2013, 12:46 PM   #20
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Thanks. I have a M Sport version but xDrive, therefore my suspension is non-sport (Thanks to the brilliant product line managers/decision makers @ BMW... ). I did have the bump stops cut as part of the Eibach install, but may put in Z4 ones anyways the next time the rear suspension is removed. Thanks again for the feedback.
I think you will see an improvement with the Z4 bumps in the back. If your factory bumps were just cut off square, they probably don't have any progression when they have to load up. The Z4 stops will feel "softer" when you do compress that far.
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      06-01-2013, 05:44 PM   #21
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I already ordered a set of e36 m3 stops for the front and I'll be replacing the cut ones above with the Z4 or e46 m3 bumps, whatever works better when I get them in.
Where did you order the Z4 bump stops from? I ordered some from FCPEuro.com and believe they sent me the wrong one. Btw, did you order the Z4 bump stops for an E85? Also, do I order the Z4 bump stops for the front or the rear?
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      06-01-2013, 05:49 PM   #22
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Where did you order the Z4 bump stops from? I ordered some from FCPEuro.com and believe they sent me the wrong one. Btw, did you order the Z4 bump stops for an E85? Also, do I order the Z4 bump stops for the front or the rear?
Commented on your other thread. Check getbmwparts.com (Formerly Tischer) or Turner, ECS, etc. The PN is 33536770350
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