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      11-22-2011, 03:09 PM   #1
jwong77
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Purchased BMW Performance Suspension springs, pair with shorter bump stops?

Hi All,

I purchased the BMW Performance Suspension springs (Yellow Springs). I intend to pair them with Koni FSD struts. I like the idea of increasing the amount of suspension travel (for a better ride). Is there any harm in replacing the bump stops with ones from an E36 M3, for the purpose of increasing suspension travel?

My goal is to maintain a good ride.

For those who know, since the BMW performance springs are supposed to lower the car only by 25MM from the normal sports suspension, is there any chance I can get away with staying with the bump stops I currently have?

Thanks in advanced for anybody's input.

Best Regards,
Jimmy
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      11-22-2011, 03:38 PM   #2
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BMW engineers use shorter/(stiffer?) bumpstops with the yellow performance springs for a reason. Unfortunately, you can't buy them seperate from the performance suspension kit and that's why I haven't bought those springs. Maybe Dinan will sell you the bumpstops from their E9X kit since their sport springs seem to be similar to the BMW PS?
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      11-22-2011, 04:59 PM   #3
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Quote:
Originally Posted by cvc 22349a View Post
BMW engineers use shorter/(stiffer?) bumpstops with the yellow performance springs for a reason. Unfortunately, you can't buy them seperate from the performance suspension kit and that's why I haven't bought those springs. Maybe Dinan will sell you the bumpstops from their E9X kit since their sport springs seem to be similar to the BMW PS?
Thanks!

I thought so too. I've read somewhere that the E36 M3 bump stop is what Dinan uses. I believe the reason for the shorter bumpstop is to increase suspension travel.

Does anybody know for sure?
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      11-22-2011, 07:39 PM   #4
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I'm sure the reason is to increase bump travel when lowering the car.
Were you able to get confirmation from Dinan as to which bumpstops they include w/their kits?
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      11-22-2011, 08:22 PM   #5
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Quote:
Originally Posted by jwong77 View Post
Thanks!

I thought so too. I've read somewhere that the E36 M3 bump stop is what Dinan uses. I believe the reason for the shorter bumpstop is to increase suspension travel.

Does anybody know for sure?
Yes, that's exactly what it's for. Steve Dinan wrote a short article on it.

By the way I don't think it will drop 25 mm from sports suspension height. But it depends which springs you got, I guess.

Use E36 M3 (see realoem.com for p/n) in front and get 33 53 6 770 350 (you need two) for the rear.
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      11-22-2011, 09:00 PM   #6
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where did you buy the springs from? I was looking to do the same...although with Koni Yellow
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      11-22-2011, 09:21 PM   #7
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^ Any BMW dealer. I've been looking to pair BMW PS springs w/Koni sports for a while but couln't find a bumpstop solution. This might be it

Luckyu: is that e36 m3 bumpstops front and rear? Do you know if the rears are attched to dust tubes?
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      11-22-2011, 10:53 PM   #8
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Thanks for the input all, the community here is great.

As for the exact drop, here is what BMW states. I was wrong, as I have the Sport Suspension (I believe all E92's had this suspension).

Quote:
This new aggressive package lowers the vehicle by 25 mm compared to the standard suspension and by 10mm when compared to the sport suspension.
So I'll really only be lowering by about 10mm.

From RealOEM.com, I found that the P/N for the front E36 M3 struts is 31332225377.

I think I'll just purchase it from Tischer and see if I can get a deal on the shipping.
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      11-22-2011, 11:11 PM   #9
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Quote:
Originally Posted by luckyu View Post
Use E36 M3 (see realoem.com for p/n) in front and get 33 53 6 770 350 (you need two) for the rear.
Hi LuckyU,

Are you sure about that PN for the rear?

After looking at RealOEM for a E36 M3, I found the following P/N
33531138109
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      11-22-2011, 11:19 PM   #10
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I'm interested to hear if this makes a difference. I've had the BMW performance springs for the past year with Koni yellows. The setup works great. A few vendors here advised me that the bumpstops wouldn't make a difference if you had ZSP bumpstops. I had ZSP so the car is not lowered that dramatically.

My ride is quite firm but much more controlled and confident than ZSP. There's a little bit of bounciness if you don't tighten the Konis. Mine are 75% to firm in front and 50% to firm in back. I am told there are some other weak points in the suspension that are hard to address which contribute to a bit of bounciness, including the rear wishbone rubber saddles and the front/rear shock mounts. And of course runflats and the rear subframe bushings; I have replaced the bushings with the M3 ones and got rid of the runflats.

Look forward to hearing how this turns out.
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      11-22-2011, 11:28 PM   #11
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Quote:
Originally Posted by jwong77 View Post
Hi LuckyU,

Are you sure about that PN for the rear?

After looking at RealOEM for a E36 M3, I found the following P/N
33531138109
That's the rear bump stop & dust tube for E85 Z4. It's what I have on my car. It's 2.5" long.

P/N for E36 M3 front is 31332225377
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      11-23-2011, 12:14 AM   #12
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Quote:
Originally Posted by cvc 22349a View Post
[...] Maybe Dinan will sell you the bumpstops from their E9X kit since their sport springs seem to be similar to the BMW PS?
It's known that the E36 M3 front bump stop is used in the Dinan M3 lowering kit, because of the white paper that Steve wrote up, and b/c rldzhao bought the Dinan kit for his M3 and did an exposť...

I'm almost certain that the Z4 bump stop is used in at least one of their kits, don't know if it's E9x or M3. 335iSSA says Evan Winstead (parts manager at Tischer BMW) checked with Dinan about it, and Dinan confirmed they're using the Z4 part.

Ideally, it would be best to engineer the correct bump stop, and you could buy Eibach or Koni bump stops, selecting from a variety of curves and lengths. But who knows how to do this correctly? I don't!

What I'm trying to do on my car is get the bump stops "out of the way" so they don't upset the car. I really hated that.

The risk of shortening the bump stop is that it reduces your spring rate in a turn. In the front, the added spring rate keeps the front McPherson geometry from going wrong and taking away your negative camber; in the rear it may partly make up for a weak rear sway bar, stiffening up the rear to reduce understeer, plus, it again keeps the rear geometry out of its "bad place".

AFAIK the details on BMW's intent with their bump stop design is still a bit of a mystery, but I think that covers two important aspects.

You're only shortening them a little with these parts, and I don't think we're far off optimal. However. What's optimal in the rear depends a lot on whether you have the M3 rear roll bar or not. You may get some (additional) understeer, be prepared for that.

Click my sig for more info on my setup.
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      11-23-2011, 12:19 AM   #13
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Quote:
Originally Posted by jwong77 View Post
Hi LuckyU,

Are you sure about that PN for the rear?

After looking at RealOEM for a E36 M3, I found the following P/N
33531138109
Does that come with the dust tube for the rear shock?
Do you know if these are the bumpstops Dinan uses for the e9x?

A side note: you can get the front BMW PS bumpstops seperate from the kit from Tischer, just not the rears..
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      11-23-2011, 02:02 PM   #14
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^ do you know what the part number is for the front BMW PS bumpstops.

Also is there a DIY for trimming bump stops?
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      11-23-2011, 03:55 PM   #15
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Quote:
Originally Posted by swifty View Post
^ do you know what the part number is for the front BMW PS bumpstops.

Also is there a DIY for trimming bump stops?
no. tischer can get it for you. personally, i'm not trimming bumpstops.
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      11-23-2011, 04:22 PM   #16
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Quote:
Originally Posted by cvc 22349a View Post
no. tischer can get it for you. personally, i'm not trimming bumpstops.
I agree, I read the article that Steve Dinan wrote about bump stops. Its pretty interesting. According to him, the M3 only has .5 inches of suspension travel where the bump stop is not in contact. Any further compression beyond .5 inches, you are actually riding on the bump stop. Now, the reason against trimming the existing bump stop, is that the bump stop is similar to a progressive rate spring. At first, it is very soft, but as you compress the bumpstop further, the harder it gets. Trimming the existing bump stop does not seem like a good idea, similar to why cutting a progressive rate spring is not a good idea. At least thats what I gathered.

For more information, here is an interesting white paper written by somebody on the M3post forum.

http://www.m3post.com/forums/showthread.php?t=427147
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      11-23-2011, 05:31 PM   #17
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Quote:
Originally Posted by cvc 22349a View Post
no. tischer can get it for you. personally, i'm not trimming bumpstops.
Thanks.

Does anyone know the difference in size between the ZSP bumpstop and the Bmw PS bumpstop. Any pics of the 2 side by side.
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      11-23-2011, 05:50 PM   #18
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I don't know the part numbers for e90 Performance Suspension, but these are the part numbers for 135i Performance Suspension:

Quote:
Originally Posted by M2 View Post
The bmw perf springs:

31336788893, fronts, each (so order 2)
33536788899, rears, each (so order 2)

The bump stops are:

31331096099, fronts, each (so order 2)
33536788905, rears, each (so order 2)
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      11-23-2011, 11:21 PM   #19
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Quote:
Originally Posted by GaryS View Post
I don't know the part numbers for e90 Performance Suspension, but these are the part numbers for 135i Performance Suspension:

The bmw perf springs:

31336788893, fronts, each (so order 2)
33536788899, rears, each (so order 2)

The bump stops are:

31331096099, fronts, each (so order 2)
33536788905, rears, each (so order 2)
The bumpstops are reported by realoem: fronts = for Z8, rears = for euro-only e91.

I'd really like this confirmed...
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      11-24-2011, 08:04 AM   #20
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I'm surprised that no one has uploaded a parts list for the e90 Performance Suspension. Here's the 135i PS parts list, which confirms the part numbers I posted yesterday.
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      11-24-2011, 02:17 PM   #21
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^ thx Gary. Where would one find the performance susp parts list for the 335i? I've tried several dealers and no one can get the rear bumpstops w/dust tubes seperate from the kit.
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      11-24-2011, 04:42 PM   #22
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Quote:
Originally Posted by cvc 22349a View Post
^ thx Gary. Where would one find the performance susp parts list for the 335i?
I can't remember who posted the 135i parts list, but I do remember he said it was in the box with the kit.
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