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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > All-Wheel-Drive (Xi / xDrive) Talk > lowered, z3m bumpstops, pothole explosion question



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      01-03-2013, 08:52 PM   #1
critical05
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lowered, z3m bumpstops, pothole explosion question

Have a e92xi lowered with eibach and koni yellow. The front struts are set to 1.5 from soft. On large road imperfectons at 60 mph I get the jarring bam like the suspension has bottom out. On elevated larger bumps like frozen ice patches at 40 mph, get the jarring BAM sound as I suspect is similar to the documented 'pothole explosion.'

When I installed the setup, I cut the front bumpstops as there was no suspension travel and holding the car up. I see a lot of 335i people have installed the z3m (e36 M3) bump stops because they are much shorter. I am wondering if anyone with lowering springs, upgraded struts, and the shorter z3m bump stops still experience the dreaded pothole explosion?

Trying to figure if i swap out the bump stops it will give me the extra suspension travel to get rid of that jaw jarring thud.

Please don't lecture me about me cutting the bump stops as now I might need to tackle this in the cold winter. The eibach instructions indicated no cutting was needed on the fronts but I found out after everything was installed, the bump stop was interfering and had to be shorten. Just trying to figure if the shorter more progressive bump stop will fix my problem.

Last edited by critical05; 01-04-2013 at 11:59 AM.
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      01-04-2013, 12:49 AM   #2
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Maybe stiffen up your koni's a bit to help take some of the load off the springs / Bam off of the bstops?
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      01-04-2013, 06:24 AM   #3
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Pe90X, Konis are only rebound adjustable.

OP, have the same K/E set up and I used the e36 M3 stops in front, without cutting them. They are significantly shorter than OEM. Have had no problems even on nasty winter ice-rutted roads.

How much did you cut down the front stops you are using now, and which part did you use (top or bottom)? The top is thicker and harder, the bottom is tapered, and much softer.

BTW the Eibach instructions do recommend cutting bump stops, I cut the rears one inch and used the e36 in front.

I would also SOFTEN the front susp to only 0.5 turns from full soft and see if that helps. You can get a phenomenon called jacking with too much rebound damping where the susp does not fully extend and then it is too compressed for the next bump. This would happen more when very cold. I'd try that first before doing anything else.

I have read that the adjuster on these Konis is not exactly linear, so that at 1.5 turns off full soft you may be running max stiff or very near it. Anyway try running full soft (at least 1/4 turn off the stop).
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      01-04-2013, 08:34 AM   #4
critical05
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Thanks, that's what I needed to hear. I just ordered the new bump stops and plan on swapping them out.

I'll try adjusting the settings as well.
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      01-04-2013, 08:53 AM   #5
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Quote:
Originally Posted by critical05 View Post
Thanks, that's what I needed to hear. I just ordered the new bump stops and plan on swapping them out.

I'll try adjusting the settings as well.
No problem. FYI I am running 0.5 from full soft on mine up here at 8000 ft elevation, tons of snow and very cold. No bottoming or other problems. With it lowered the wheel wells are filling up with snow and ice pretty fast though. So if you are seeing lots of snow where you are some of the noise you hear may also be stuff banging on ice up in there.
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      01-04-2013, 12:05 PM   #6
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ajsalida, I thought you had an 335xi? I assume the e36 M3 listed on your profile is your summer car?

Does the e36 m3 bumpstop fit on the original dust cover?
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      01-04-2013, 02:08 PM   #7
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Quote:
Originally Posted by critical05 View Post
ajsalida, I thought you had an 335xi? I assume the e36 M3 listed on your profile is your summer car?

Does the e36 m3 bumpstop fit on the original dust cover?
I have both cars, & both have Koni/Eibach. e36 m3 stop fits inside the e9x dust cover. it is pretty obvious how it goes once you look at it.
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      01-04-2013, 04:58 PM   #8
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Whats your setting for the rear shocks? Also hows the ride with passengers in the back seat? My is set at 1.25 and with passengers in the rear, it can get bouncy on wavy roads.
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      01-04-2013, 05:52 PM   #9
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I set both front and rear to 0.5 turns off soft, I live on a dirt road, local paved roads suck too, and have harsh winters so starting off soft was my going in assumption. So far so good. I have an e92 335xi so not many passengers in back. If you did not trim the rear bump stops you ought to. You'd definitely be riding on them with 2 passengers if not trimmed.
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      01-04-2013, 07:25 PM   #10
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I trimmed the rears as eibachs instructions stated. I have a coupe as well and sometimes I have to drive for lunch so that's where the back passengers come into play. Driving alone or with a passenger, the backs not bad, only when I have a full car.

I think I can wait til spring when i swap out my winter tires to readjust the rears. I'll do what others have done by cutting an access hole to remove the top shock nut so I don't have to remove all the trunk liners. The sheet metal plugs you can get at menards will cover up the holes and make for a clean mod.

I just adjusted the fronts this evening and will see if its better. Bump stops come Wednesday, got them and new dust covers for $29 shipped from fcpeuro.com

Keeping my fingers crossed and hope next weekends temps aren't too bad to swap them out.
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      01-05-2013, 09:01 AM   #11
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Good luck, keep us posted.
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      01-06-2013, 12:48 PM   #12
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So I tackled readjusting the rear koni shocks this morning at 14 degrees outside in a non heated garage. Removing the trunk lining the second time around took me less than 15 min so its not worth cutting the liner to make an access hole. One could take the large rubber cover on top of the shock, under the liner, and cut the liner to fit the existing cover.

I did NOT have to remove the shock from the car to adjust it. I removed the wheel, with the top shock nut removed, compressed the rod, and with my torx screwdriver turned the rod all within the wheelwell. Best part is that i didn't have to get under the car. Its now set to 0.5 from full soft. Overall it took just a tad over an hour.

Did notice some minor crevis corrosion on top of the shock body already.

Plan to replace the front bumpstops next weekend.
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      01-07-2013, 06:37 AM   #13
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Quote:
Originally Posted by critical05 View Post
So I tackled readjusting the rear koni shocks this morning at 14 degrees outside in a non heated garage. Removing the trunk lining the second time around took me less than 15 min so its not worth cutting the liner to make an access hole. One could take the large rubber cover on top of the shock, under the liner, and cut the liner to fit the existing cover.

I did NOT have to remove the shock from the car to adjust it. I removed the wheel, with the top shock nut removed, compressed the rod, and with my torx screwdriver turned the rod all within the wheelwell. Best part is that i didn't have to get under the car. Its now set to 0.5 from full soft. Overall it took just a tad over an hour.

Did notice some minor crevis corrosion on top of the shock body already.

Plan to replace the front bumpstops next weekend.
That is pretty clever. Did you take the bumpstop and dust boot off before you adjusted it? I tried to do that (adjust the rear) with the bumpstop and boot on before I installed them, and couldn't compress it all the way down to the detent even outside of the car.

Any feedback on the pothole problem?
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      01-09-2013, 07:18 PM   #14
critical05
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Yeah the dust boot and bump stop were removed. When you fully compress the shock, there isn't much showing except the threaded portion.

May have been fretting too much about some of the situations where the suspension bottomed out. I just remembered that my z32 (300zx) used to bottom out as well at that same spot. Still planning on swappin the front bumpstops out, can't hurt to have more suspension travel.
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      01-10-2013, 07:28 AM   #15
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Great to know you can do that, taking the shock out all the way is a PITA. I did not find taking the carpet & trim out to be that big of a deal, compared to other cars with SA konis. Personally I would not cut the carpet for future resale purposes.
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      01-11-2013, 12:29 PM   #16
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Bump stops replaced last night, took today off to get it done before the weekend. Couldn't wait and didn't take as long as expected, about three hours. Just took it out for a short spin today not long enough to form an opinion just yet, will have to see if the progressive portion of the bump stop makes ofr softer suspension bottoming.
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      01-11-2013, 12:46 PM   #17
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Lets see how that works out.

I got the same setup and I like it. I had the bump stops cut out as the instructions state.
I do believe that the Eibach springs (designed for 335i not xi) dont handle the weight of the XDrive well, reason why the feel of bottoming out on bumps.
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      01-11-2013, 03:18 PM   #18
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Quote:
Originally Posted by vapore0n View Post
Lets see how that works out.

I got the same setup and I like it. I had the bump stops cut out as the instructions state.
I do believe that the Eibach springs (designed for 335i not xi) dont handle the weight of the XDrive well, reason why the feel of bottoming out on bumps.
A lot of the extra weight in front on the Xi is unsprung. I.e. hubs, axles, outer CV joints, & heavier lower susp pieces, are not supported by the springs. FWIW I have had no bottoming problems, in fact fewer/none compared to stock which was terrible, even on non RFT Conti DWS. And weight wise my car is a pig, Xi + AT using the same Eibachs as non-Xi MT.

This fact still blows me away, that a much lower + stiffer "sportier" susp bottoms less and feels so much better on terrible roads. In fact I never would have believed it had I not previously put the same K/E susp on my other car (e36 M3) and it soaked up bumps like magic, far better than the stock 335Xi. So I thought WTH go for same set up on the Xi.
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      01-12-2013, 01:58 PM   #19
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Hits some big bumps today that I know are normally harsh, the suspension was more controlled and muffled. Can't say if its stopped bottoming out or if the bump stops just make for a softer controlled bottoming out. Not the best description, but its an hundred times better.

Even on smaller bumps, the bumps seem more muffled so i think that there really isn't much suspension travel before the strut body hits the bump stop. Took a pic (not raised, normal lowered stance) and you can see the top of the bump stops and the spring perch, you gotta remember that you see only the top portion of the bump stop and there is about an inch between the lower spring perch and the top of the strut body. Not really too much room in there. I'm happy with the shorter bumpstops!

Also if you look at the spacing of the coils vs the available strut travel, the available strut travel is taken up before the spring can bottom out (also backed up by the dirt water marks in between the coils)
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Last edited by critical05; 01-12-2013 at 02:10 PM.
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      01-13-2013, 10:15 AM   #20
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Great results, hope your problems are all gone.
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      04-16-2013, 02:01 PM   #21
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Been reading these threads. Thanks for the write up. Does anyone have the specific PN for the bumpstops? Trying to get all the parts together for the pending change over to Koni/Eibach... I have read E36 M3 (as you noted above) for the front, and Z4 for the back but not sure about the rear... Also which dust covers/boot? Thanks for the info advance!

Last edited by thegrinchboy; 04-16-2013 at 02:47 PM.
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      04-16-2013, 04:43 PM   #22
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http://www.e90post.com/forums/showthread.php?t=814809

About halfway down the page.

For the rears you just cut the bump stops per eibach instructions. I just used a universal bellow style you cut and zip tie the ends for the rear dust cover.
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